Samacheer Kalvi Class 10 Science Solutions Chapter 6 Nuclear Physics

Column I	Column II
(a) Co-60	(i) Age of fossil
(b) I-131	(ii) Function of Heart
(c) Na-11	(iii) Leukemia
(d) C-14	(iv) Thyroid disease

Answer:
(a) – (iii)
(b) – (iv)
(c) – (ii)
(d) - (i)
In simple words: Cobalt-60 treats leukemia, Iodine-131 helps with thyroid disease, Sodium-24 checks heart function, and Carbon-14 is used to date fossils. Each radioisotope has a specific role in medicine or dating.

🎯 Exam Tip: Create a mental map or flashcards for common radioisotopes and their applications in various fields like medicine, industry, and carbon dating.

 

V. Arrange the Following in the Correct Sequence.

 

Question 1. Arrange in descending order, on the basis of their penetration power. Alpha rays, beta rays, gamma rays, cosmic rays
Answer: cosmic rays > gamma rays > beta rays > alpha rays
In simple words: Cosmic rays can go through the most, followed by gamma rays, then beta rays, and finally alpha rays which are easily stopped. This order shows how much material each type of radiation can pass through.

🎯 Exam Tip: Remember the penetrating power order: cosmic rays are highest, then gamma, beta, and alpha is lowest. This is crucial for radiation shielding and safety protocols.

 

Question 2. Arrange the following in the chronological order of discovery. Nuclear reactor, radioactivity, artificial radioactivity, discovery of radium.
Answer: Discovery of radium, Radioactivity, Artificial radioactivity, Nuclear reactor.
In simple words: Radium was found first, then the general idea of radioactivity, followed by making materials radioactive, and finally building nuclear reactors. This order shows the progress of scientific understanding and technology.

🎯 Exam Tip: Knowing the historical sequence of major discoveries helps to understand the evolution of scientific thought in nuclear physics.

 

VI. Use the Analogy to Fill in the Blank.

 

Question 1. Spontaneous process : Natural Radioactivity, Induced process : ............
Answer: Artificial Radioactivity
In simple words: Natural radioactivity happens on its own, like a spontaneous process. When we make something radioactive, that's an induced process, also called artificial radioactivity.

🎯 Exam Tip: Distinguish between "spontaneous" (natural) and "induced" (artificial) processes in radioactivity. This is a fundamental concept.

 

Question 2. Nuclear Fusion : Extreme temperature, Nuclear Fission: ............
Answer: Atomic bomb
In simple words: Nuclear fusion needs extremely high temperatures to occur, like in the sun. Nuclear fission, on the other hand, is the process used in atomic bombs to release energy.

🎯 Exam Tip: Relate nuclear fusion to high temperatures and stellar processes, and nuclear fission to both atomic bombs and nuclear reactors.

 

Question 3. Increasing crops : Radio phosphorous, Effective functioning of heart : ............
Answer: Radio sodium
In simple words: Just as radio phosphorous helps make crops grow better, radio sodium is used to check if the heart is working properly. Both are medical and agricultural applications of radioisotopes.

🎯 Exam Tip: Understand that various radioisotopes have specific applications in different fields, such as agriculture and medicine. Sodium-24 is used for blood flow studies.

 

Question 4. Deflected by electric field : \( \alpha \) ray, No Deflection : ............
Answer: \( \gamma \)-ray
In simple words: Alpha rays are positively charged, so they bend in an electric field. Gamma rays have no charge, so they go straight through without bending.

🎯 Exam Tip: Remember that charged particles (alpha, beta) are deflected by electric and magnetic fields, while neutral particles (gamma, neutrons) are not.

 

VII. Numerical Problems.

 

Question 1. \( _{88}Ra^{226} \) experiences three \( \alpha \) – decay. Find the number of neutrons in the daughter element.
Answer:
Mass number of \( Ra^{226} \) is 226
Atomic number of \( Ra^{226} \) is 88
Mass number of \( \alpha \) = 4
Atomic number of \( \alpha \) = 2
After 3 \( \alpha \) decay:
Mass number of the daughter element is
\( = 226 - (3 \times 4) \)
\( = 226 - 12 \)
\( = 214 \)
Atomic number of the daughter element is
\( = 88 - (3 \times 2) \)
\( = 88 - 6 \)
\( = 82 \)
Number of neutrons is
\( = \text{Mass number - Atomic number} \)
\( = 214 - 82 \)
\( = 132 \)
In simple words: When a radioactive element undergoes alpha decay three times, its mass decreases by 12 and its atomic number decreases by 6. By calculating these changes, we find the new mass and atomic number, which then lets us figure out the number of neutrons in the new element.

🎯 Exam Tip: For alpha decay, consistently subtract 4 from the mass number and 2 from the atomic number for each decay. The number of neutrons is always mass number minus atomic number.

 

Question 2. A cobalt specimen induced radiation of 75.6 millicurie per second. Convert this disintegration in to becquerel (one curie = \( 3.7 \times 10^{10} \) Bq).
Answer:
1 curie \( = 3.7 \times 10^{10} \) Bq
\( \implies \) 75.6 \( \times 10^{-3} \) curie \( = 75.6 \times 10^{-3} \times 3.7 \times 10^{10} \)
\( = 279.72 \times 10^{7} \) Bq
\( = 279.72 \times 10^{7} \) Becquerel
In simple words: To change millicuries into becquerels, we first convert millicuries to curies, then multiply by the conversion factor for 1 curie to becquerel. This calculation helps us understand the radiation activity in standard SI units.

🎯 Exam Tip: Remember the conversion factor: 1 curie = \( 3.7 \times 10^{10} \) Bq. Pay attention to prefixes like "milli" ( \( 10^{-3} \) ) during calculations.

 

VIII. Assertion and Reason Type Questions.

 

Question 1. Assertion: A neutron impinging on \( U^{235} \), splits it to produce Barium and Krypton. Reason: \( U – 235 \) is a fissile material.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
In simple words: The assertion is true because uranium-235 splits into barium and krypton when hit by a neutron. The reason is also true and explains why this happens: uranium-235 is fissile, meaning it can easily undergo fission.

🎯 Exam Tip: For assertion-reason questions, first determine if each statement is true or false individually. If both are true, then evaluate if the reason correctly explains the assertion.

 

Question 2. Assertion: In a \( \beta \) – decay, the neutron number decreases by one. Reason: In \( \beta \) – decay atomic number increases by one.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
In simple words: In beta decay, a neutron changes into a proton and an electron. This means the number of neutrons goes down by one, and the number of protons (atomic number) goes up by one, making the reason a direct explanation of the assertion.

🎯 Exam Tip: Understand the mechanism of beta decay: a neutron transforms into a proton and an electron. This explains why the atomic number increases and the neutron number decreases simultaneously.

 

Question 3. Assertion: Extreme temperature is necessary to execute nuclear fusion. Reason: In a nuclear fusion, the nuclei of the reactants combine releasing high energy.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
In simple words: Very high temperatures are needed for nuclear fusion to happen because the combining nuclei must overcome strong repulsion. This fusion process releases a huge amount of energy. The energy release is what makes the high temperature necessary.

🎯 Exam Tip: The extremely high temperatures in fusion are needed to give nuclei enough kinetic energy to overcome electrostatic repulsion, allowing them to get close enough to fuse and release energy.

 

Question 4. Assertion: Control rods are known as 'neutron seeking rods'. Reason: Control rods are used to perform sustained nuclear fission reaction.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion
In simple words: Control rods are called 'neutron seeking rods' because they absorb extra neutrons, which helps keep the nuclear fission reaction steady. This absorption is key to safely controlling the reaction and making it last.

🎯 Exam Tip: Control rods are essential for regulating the chain reaction in a nuclear reactor by absorbing excess neutrons, thereby preventing the reaction from becoming uncontrolled.

 

IX. Answer in One or Two Words (VSA).

 

Question 1. Who discovered natural radioactivity?
Answer: Henri Becquerel
In simple words: Henri Becquerel was the scientist who first found out that some materials naturally give off radiation. He discovered this by accident while studying uranium salts.

🎯 Exam Tip: Accurately associating Henri Becquerel with the discovery of natural radioactivity is a key historical fact in nuclear physics.

 

Question 2. Which radioactive material is present in the ore of pitchblende?
Answer: Uranium
In simple words: Pitchblende is a mineral that naturally contains uranium, which is a radioactive element. This ore was historically important in the early studies of radioactivity.

🎯 Exam Tip: Knowing that pitchblende is a primary source of uranium is important for understanding the natural occurrence of radioactive elements.

 

Question 3. Write any two elements which are used for inducing radioactivity?
Answer: Boron and aluminium
In simple words: Boron and aluminium are two elements that can be made radioactive by hitting them with particles, which is known as induced radioactivity. This shows that even light elements can be changed to become radioactive.

🎯 Exam Tip: Remember examples of elements that can undergo artificial (induced) radioactivity, as this illustrates human capability to create new radioactive isotopes.

 

Question 4. Write the name of the electromagnetic radiation which is emitted during natural radioactivity.
Answer: Gamma rays
In simple words: Gamma rays are a type of electromagnetic radiation, like light or X-rays, that are given off naturally by some radioactive substances. They are very energetic and have no charge.

🎯 Exam Tip: Distinguish between particle radiations (alpha, beta) and electromagnetic radiation (gamma rays) in radioactive decay processes.

 

Question 5. If A is a radioactive element which emits an \( \alpha \) – particle and produces \( _{104}Rf^{259} \). Write the atomic number and mass number of the element A.
Answer:
Let the element be \( _{Z}A^{M} \)
For \( \alpha \) decay, atomic number decreases by 2 and mass number decreases by 4.
So, \( _{Z}A^{M} \xrightarrow{\alpha} _{104}Rf^{259} \)
Mass number M \( = 259 + 4 = 263 \)
Atomic number Z \( = 104 + 2 = 106 \)
Therefore, the original element A is \( _{106}Sg^{263} \) (Seaborgium).
In simple words: When an alpha particle is released, the new element has a mass number that is 4 less and an atomic number that is 2 less than the original element. So, to find the original element, we add these numbers back to the product.

🎯 Exam Tip: Always work backward with the decay rules: for alpha emission, add 4 to the daughter's mass number and 2 to its atomic number to find the parent nucleus.

 

Question 6. What is the average energy released from a single fission process?
Answer: 200 MeV
In simple words: When one atom splits in a nuclear fission event, it releases a significant amount of energy, typically around 200 mega-electron volts. This energy is much higher than what chemical reactions release.

🎯 Exam Tip: Remember the approximate energy released per fission (200 MeV), as this highlights the immense energy density of nuclear processes.

 

Question 7. Which hazardous radiation is the cause for the genetic disease?
Answer: \( \gamma \) – ray (Gamma-ray) or any high energy nuclear particle passing through a human being disrupts the entire normal functioning of the biological system, and the effect may be either pathological or genetic disease.
In simple words: Gamma rays and other strong nuclear particles are dangerous because they can damage the body's cells and DNA. This damage can lead to sickness or even changes in genes that can cause diseases that are passed on to future generations.

🎯 Exam Tip: Emphasize the DNA-damaging potential of high-energy radiation, particularly gamma rays, as the primary cause of genetic disorders and cancers.

X. Answer The Following Questions In A Few Sentences

 

Question 1. Write any three features of natural and artificial radioactivity.
Answer:

In simple words: Natural radioactivity happens on its own from heavy elements and cannot be controlled, while artificial radioactivity is started by humans in lighter elements and can be managed.

🎯 Exam Tip: When comparing, ensure you list distinct characteristics for each type and provide specific examples if asked, as this helps highlight the differences clearly.

 

Question 2. Define critical mass.
Answer: The smallest amount of fissile material needed to keep a nuclear chain reaction going on its own is called critical mass (\( m_c \)). This amount changes based on what the material is made of, how dense it is, and its size. This minimum mass is crucial for designing nuclear weapons and reactors.
In simple words: Critical mass is the smallest amount of special material needed for a nuclear chain reaction to keep happening by itself.

🎯 Exam Tip: Remember that critical mass is not a fixed value, but depends on several factors like the type of fuel, its shape, and density.

 

Question 3. Define one roentgen.
Answer: One roentgen is defined as the specific amount of a radioactive substance that makes \( 2.58 \times 10^{-4} \) coulombs of charge appear in one kilogram of air. This measurement is taken when the air is at normal pressure, temperature, and humidity. This unit is used to quantify exposure to X-rays and gamma rays.
In simple words: One roentgen is how much radioactivity makes a certain amount of electricity in one kilogram of air under normal conditions.

🎯 Exam Tip: Understand that roentgen is a unit of exposure, measuring the ionization in air caused by X-rays or gamma rays.

 

Question 4. State Soddy and Fajan's displacement law.
Answer: Soddy and Fajan's displacement law describes how the atomic and mass numbers of a nucleus change during radioactive decay:
(i) When a nucleus releases an alpha particle, the new nucleus (daughter) will have a mass number that is 4 units less and an atomic number that is 2 units less than the original (parent) nucleus. This occurs because an alpha particle is essentially a helium nucleus.
(ii) When a nucleus releases a beta particle, the new nucleus will have the same mass number, but its atomic number will increase by 1 unit compared to the parent nucleus. This happens because a neutron converts into a proton, electron (beta particle), and an antineutrino.
In simple words: This law explains how atomic numbers and mass numbers change when an atom decays, either by letting go of an alpha particle (mass goes down by 4, atomic number by 2) or a beta particle (mass stays same, atomic number goes up by 1).

🎯 Exam Tip: Always remember the specific changes to mass and atomic numbers for both alpha and beta decay, as this is fundamental to understanding nuclear transformations.

 

Question 5. Give the function of control rods in a nuclear reactor.
Answer: Control rods in a nuclear reactor have the important job of managing the number of neutrons available. Their main function is to absorb excess neutrons, which helps keep the nuclear chain reaction steady and controlled, preventing it from getting out of hand. These rods are usually made from materials like boron or cadmium, which are very good at absorbing neutrons.
In simple words: Control rods soak up extra neutrons in a nuclear reactor to keep the reaction calm and steady.

🎯 Exam Tip: Remember that control rods are essential for safety and efficiency, as they prevent the chain reaction from becoming uncontrolled and leading to overheating.

 

Question 6. In Japan, some of the newborn children are having congenital diseases. Why?
Answer: Some newborn children in Japan have congenital diseases (birth defects) because of past exposure to nuclear radiation. In certain areas, there were leaks of nuclear radiation. If pregnant women or very young children in these affected areas were exposed to these harmful radiations without proper care, it could lead to these congenital diseases. Such exposure can cause mutations in developing cells.
In simple words: Babies in some parts of Japan have birth defects because their parents, or they themselves, were exposed to harmful nuclear radiation from past leaks.

🎯 Exam Tip: Highlight the long-term, intergenerational effects of radiation exposure, particularly on genetic material and developing organisms.

 

Question 7. Mr. Ramu is working as an X - ray technician in a hospital. But, he does not wear the lead aprons. What suggestion will you give to Mr. Ramu?
Answer: Mr. Ramu, as an X-ray technician, should always wear lead aprons and practice safety measures. Even though the intensity of X-rays used in hospitals is generally low and might not cause immediate severe effects, repeated exposure over time can still be harmful. Therefore, he should wear protective lead aprons, gloves, and glasses to block radiation. Additionally, he should avoid eating or drinking in the X-ray room to prevent any potential contamination. Long-term exposure to even low-level radiation can increase health risks.
In simple words: Mr. Ramu should always wear lead aprons and other protective gear while working with X-rays, and not eat or drink in the X-ray room, because even low radiation can be harmful over time.

🎯 Exam Tip: Emphasize the importance of cumulative exposure and preventive measures like lead shielding, even for seemingly low-risk radiation sources.

 

Question 8. What is stellar energy?
Answer: Stellar energy is the immense energy produced in the cores of the Sun and other stars. This energy is generated through nuclear fusion reactions, where lighter atomic nuclei combine to form heavier nuclei under extreme temperatures and pressures, releasing a vast amount of energy. This process is what makes stars shine so brightly.
In simple words: Stellar energy is the huge amount of power that comes from the Sun and other stars, made when tiny atoms join together in their hot centers.

🎯 Exam Tip: Connect stellar energy directly to nuclear fusion, explaining that it's the fundamental power source of stars, including our Sun.

 

Question 9. Give any two uses of radio isotopes in the field of agriculture?
Answer: Radioisotopes have several uses in agriculture. Two key applications are:
1. Increasing Crop Productivity: Radioisotope Phosphorus-32 (\( P^{32} \)) is used to study how plants absorb nutrients from the soil, helping farmers figure out the best way to fertilize their crops and increase yields.
2. Pest Control and Preservation: Radiations from isotopes can be used to sterilize male insect pests, reducing their populations, or directly kill insects and parasites that damage crops. This also helps prevent the spoilage and wastage of harvested agricultural products by inhibiting sprouting and killing microbes.
In simple words: Radioisotopes help crops grow better and protect them from pests, meaning less food is wasted.

🎯 Exam Tip: When listing applications, provide a specific example for each use to demonstrate practical understanding.

 

Question 10. What is stellar energy?
Answer: Stellar energy refers to the vast amount of energy created deep within the Sun and other stars. This energy comes from nuclear fusion, a process where light atomic nuclei combine under extreme heat and pressure to form heavier nuclei, releasing tremendous energy. This continuous release of energy is why stars glow and provide heat.
In simple words: Stellar energy is the massive power generated in stars, like our Sun, through the joining of small atoms.

🎯 Exam Tip: Emphasize that nuclear fusion is the core mechanism, converting mass into energy, which is responsible for all stellar activity.

 

XI. Answer The Following Questions In Detail

 

Question 1. Explain the process of controlled and uncontrolled chain reactions.
Answer: Nuclear chain reactions can be either controlled or uncontrolled:
(i) Controlled Chain Reaction: In this process, the number of neutrons released that continue the reaction is carefully kept at an average of one. This control is achieved by using materials called neutron absorbers, which soak up excess neutrons. As a result, the reaction happens in a stable, sustained way. The energy from controlled chain reactions is used in nuclear reactors to generate electricity for peaceful purposes.
(ii) Uncontrolled Chain Reaction: Here, the number of neutrons that cause further fission increases rapidly and without limit. This causes a huge amount of fissile material to split very quickly, releasing an enormous amount of energy in just a fraction of a second. This type of reaction is the principle behind an atomic bomb, leading to a massive explosion.
In simple words: A controlled chain reaction keeps energy steady for things like power, but an uncontrolled one lets all the energy burst out at once, like in an atomic bomb.

🎯 Exam Tip: Clearly differentiate between the two types by mentioning their control mechanisms, energy release rates, and primary applications (nuclear reactors vs. atomic bombs).

 

Question 2. Compare the properties of alpha, beta and gamma radiations.
Answer:

In simple words: Alpha rays are slow, heavy, positive, and stop easily; beta rays are faster, lighter, negative, and penetrate more; gamma rays are massless, chargeless, travel at light speed, and penetrate the most.

🎯 Exam Tip: When comparing, create a clear table with distinct properties for each radiation type to show a comprehensive understanding.

 

Question 3. What is a nuclear reactor? Explain its essential parts with their functions.
Answer: A nuclear reactor is a machine designed to create a self-sustaining and controlled nuclear fission reaction, primarily to generate electricity. Its main parts and their jobs are:
1. Fuel: This is the material that splits (fissions) to produce energy. Uranium, especially \( U^{235} \), is the most common fuel used.
2. Moderator: The moderator slows down the fast-moving neutrons released during fission. Slower neutrons are more likely to cause further fission, keeping the reaction going efficiently. Materials like graphite and heavy water are often used.
3. Control Rods: These rods control the speed of the chain reaction. They are made of materials like boron or cadmium, which absorb excess neutrons, preventing the reaction from becoming too intense.
4. Coolant: The coolant removes the massive heat generated by the fission process in the reactor core. This heat is then used to boil water, creating steam that drives turbines to produce electricity. Water, air, and helium are common coolants.
5. Protection Wall: A thick wall, usually made of concrete and lead, surrounds the reactor. Its purpose is to stop harmful radiation from leaking out and protect people and the environment.
In simple words: A nuclear reactor makes electricity by splitting atoms in a controlled way, using fuel, a moderator to slow things down, control rods to manage the reaction, a coolant to take away heat, and thick walls for safety.

🎯 Exam Tip: For this question, describing each component's function concisely is crucial to illustrate how a nuclear reactor operates safely and efficiently.

 

XII. HOT Questions

 

Question 1. The mass number of a radioactive element is 232 and its atomic number is 90. When this element undergoes certain nuclear reactions, it transforms into an element with a mass number 208 and an atomic number 82. Determine the number of alpha and beta decay that can occur.
Answer: Let the initial element be \( _{90}X^{232} \) and the final element be \( _{82}Pb^{208} \).
Let the number of alpha decays be \( n_\alpha \) and beta decays be \( n_\beta \).
Each alpha decay (\( \alpha \)-particle, \( _{2}He^{4} \)) reduces mass number by 4 and atomic number by 2.
Each beta decay (\( \beta \)-particle, \( _{-1}e^{0} \)) keeps mass number the same and increases atomic number by 1.

**1. Calculate number of alpha decays (\( n_\alpha \)):**
Change in Mass Number = Initial Mass Number - Final Mass Number
\( 232 - 208 = 24 \)
Since only alpha decay changes mass number, \( n_\alpha \times 4 = 24 \)
\( n_\alpha = \frac{24}{4} = 6 \)
So, there are 6 alpha decays.

**2. Calculate number of beta decays (\( n_\beta \)):**
Change in Atomic Number from \( \alpha \) decays = \( n_\alpha \times 2 = 6 \times 2 = 12 \).
Atomic number after 6 alpha decays = Initial Atomic Number - Change from \( \alpha \) decays \( = 90 - 12 = 78 \).
The final atomic number is 82.
The difference in atomic number due to beta decays = Final Atomic Number - Atomic number after \( \alpha \) decays \( = 82 - 78 = 4 \).
Since each beta decay increases the atomic number by 1, \( n_\beta \times 1 = 4 \)
\( n_\beta = 4 \)
Thus, there are 4 beta decays.

The number of alpha decay = 6
The number of beta decay = 4.
In simple words: To get from the starting atom to the final atom, 6 alpha particles and 4 beta particles must have been released.

🎯 Exam Tip: Always tackle mass number changes first to determine alpha decays, as beta decay does not affect mass number. Then use the remaining atomic number change to find beta decays.

 

Question 2. 'X - rays should not be taken often'. Give the reason.
Answer: X-rays should not be taken often because even though medical X-rays use low intensity radiation, repeated exposure can be harmful to the human body. While a single X-ray might have minimal effects, cumulative exposure can damage cells and tissues, potentially leading to skin problems, damage to deeper tissues around bones, and an increased risk of long-term health issues like cancer. This is why medical professionals use lead shielding and limit X-ray frequency.
In simple words: Too many X-rays can harm your body's cells and tissues over time, even if each one is low power.

🎯 Exam Tip: Focus on the cumulative effect of radiation and the potential for cellular damage over time, rather than just immediate effects.

 

Question 3. Cell phone towers should be placed far away from the residential area - why?
Answer: Cell phone towers should ideally be placed far away from residential areas because they emit microwaves, a form of electromagnetic radiation. These microwaves are scattered over a certain area, and continuous or frequent exposure to them, especially for vulnerable groups like small children and elderly people, might pose health risks. While studies are ongoing, prolonged exposure could potentially affect biological systems and lead to adverse health effects. This is a topic of ongoing research and public concern.
In simple words: Cell phone towers send out microwaves, and keeping them away from homes protects children and older people from possible long-term health risks.

🎯 Exam Tip: Mention the specific type of radiation (microwaves) and highlight the precautionary principle due to potential long-term health effects on sensitive populations.

 

I. Choose The Correct Answer.

 

Question 1. The elements that undergo spontaneous radioactivity:
(a) Uranium
(b) Radium
(c) Uranium and Radium
(d) None of the options
Answer: (c) Uranium and Radium
In simple words: Uranium and Radium are natural elements that decay by themselves, releasing radiation without any external help. This self-decay is called spontaneous radioactivity.

🎯 Exam Tip: Remember that spontaneous radioactivity is a natural property of certain heavy, unstable elements like uranium and radium.

 

Question 2. The artificial (or) induced radioactive element is _____
(a) Uranium
(b) Boron
(c) Radium
(d) None of these.
Answer: (b) Boron
In simple words: Boron can be made radioactive by causing it to react, which is called artificial or induced radioactivity. Uranium and Radium are naturally radioactive.

🎯 Exam Tip: Distinguish between natural (from unstable heavy nuclei) and artificial (induced in lighter nuclei through bombardment) radioactivity.

 

Question 3. The nucleons in a nucleus are attracted by:
(a) electrostatic force
(b) gravitational force
(c) nuclear force
(d) magnetic force
Answer: (c) nuclear force
In simple words: The strong nuclear force is what holds the protons and neutrons (together called nucleons) tightly inside an atom's nucleus, overcoming other repelling forces.

🎯 Exam Tip: Understand that the strong nuclear force is the strongest fundamental force, responsible for the stability of atomic nuclei.

 

Question 4. In beta decay by one.
(b) atomic number decreases
(c) neutron number decreases
(d) proton number decreases
Answer: (c) neutron number decreases
In simple words: In beta-minus decay (often simply called beta decay), a neutron changes into a proton, releasing an electron. So, the number of neutrons in the nucleus goes down by one.

🎯 Exam Tip: Recall that beta decay involves the transformation of a neutron into a proton, which increases the atomic number by one while decreasing the neutron count.

 

Question 5. The charge of the \( \alpha \) rays _____
(a) \( 2e \)
(b) \( -e \)
(c) 0
(d) None of these.
Answer: (a) \( 2e \)
In simple words: Alpha rays are made of alpha particles, which are like helium nuclei. Each alpha particle has two protons, so its charge is \( +2e \).

🎯 Exam Tip: Remember that an alpha particle is a helium nucleus, meaning it has 2 protons and thus a positive charge of \( +2e \).

 

Question 6. In which process positron is emitted?
(a) natural radioactivity
(b) artificial radioactivity
(c) nuclear fission
(d) nuclear fusion
Answer: (b) artificial radioactivity
In simple words: Positrons are typically emitted during artificial radioactivity, specifically in a process called beta-plus decay, where a proton turns into a neutron and a positron is released. This process is often induced in laboratories.

🎯 Exam Tip: Recognize that positron emission (beta-plus decay) is characteristic of artificial radioactivity, where proton-rich nuclei transform.

 

Question 7. The atomic number of the elements that exhibit natural radioactivity is:
(a) less than 83
(b) more than 83
(c) more than 42
(d) more than 82
Answer: (b) more than 83
In simple words: Elements with an atomic number greater than 83 are naturally unstable and undergo radioactive decay on their own. This is a common characteristic of heavy elements.

🎯 Exam Tip: Key takeaway: elements heavier than bismuth (atomic number 83) are generally naturally radioactive due to nuclear instability.

 

Question 8. The ionising power of the \( \alpha \) rays _____
(a) 100 times greater than the \( \beta \) rays
(b) 1000 times greater than the \( \gamma \) rays
(c) very less ionization
(d) both (a) and (b).
Answer: (d) both (a) and (b)
In simple words: Alpha particles are much heavier and carry more charge than beta or gamma rays. This means they can knock electrons off other atoms much more easily, making them highly effective at ionization.

🎯 Exam Tip: Remember the relationship between particle mass, charge, and ionizing power; heavier and more charged particles cause more ionization.

 

Question 9. In the reaction \( _4Be^9 + \alpha \longrightarrow X + _0n^1 \) is:
(a) \( _6C^{13} \)
(b) \( _6C^{12} \)
(c) \( _7N^{13} \)
(d) \( _8O^{16} \)
Answer: (b) \( _6C^{12} \)
In simple words: When Beryllium-9 is bombarded with an alpha particle, it transforms into Carbon-12 and releases a neutron. This reaction shows how new elements can be formed through nuclear bombardment.

🎯 Exam Tip: For nuclear reactions, always balance both the mass number (top) and atomic number (bottom) on both sides of the equation.

 

Question 10. Ionising power of \( \beta \) rays _____
(a) 100 times greater than \( \alpha \) rays
(b) 100 times less than \( \alpha \) rays
(c) comparatively very less ionization power
(d) 1000 times less than \( \gamma \) rays.
Answer: (b) 100 times less than \( \alpha \) rays
In simple words: Beta rays are lighter and move faster than alpha rays, so they are not as good at knocking electrons off other atoms. Alpha rays are much better ionizers.

🎯 Exam Tip: Understand that while beta rays have more penetrating power than alpha rays, their ionizing power is significantly lower due to their smaller mass and higher speed.

 

Question 11. During \( \alpha \) - decay the mass number of the daughter element is:
(a) more by 2 units
(b) less by 2 units
(c) more by 4 units
(d) less by 4 units
Answer: (d) less by 4 units
In simple words: When an atom undergoes alpha decay, it releases an alpha particle, which has a mass number of 4. This means the remaining daughter nucleus will have a mass number that is 4 units smaller than the original atom.

🎯 Exam Tip: Associate alpha decay directly with the emission of a helium nucleus, leading to a decrease of 4 in mass number and 2 in atomic number.

 

Question 12. When \( \alpha \) - particle is emitted the atomic number of daughter element is:
(a) more by 4 units
(b) less by 4 units
(c) less by 2 units
(d) more by 2 units
Answer: (c) less by 2 units
In simple words: An alpha particle consists of two protons. So, when it's emitted during decay, the atomic number (which is the number of protons) of the original nucleus decreases by two.

🎯 Exam Tip: Remember that the atomic number is defined by the number of protons, so alpha decay directly reduces this by two.

 

Question 13. Which power has more penetrating power?
(a) \( \alpha \) rays
(b) \( \gamma \) rays
(c) \( \beta \) rays
(d) X rays.
Answer: (b) \( \gamma \) rays
In simple words: Gamma rays are high-energy electromagnetic waves with no mass or charge, allowing them to pass through many materials much more easily than alpha or beta particles, giving them the highest penetrating power.

🎯 Exam Tip: Always rank the penetrating powers as gamma > beta > alpha due to their different masses, charges, and interaction properties.

 

Question 14. What is the charge of alpha particle?
(a) -e
(b) +e
(d) +2e
Answer: (d) +2e
In simple words: An alpha particle is made of two protons and two neutrons. Since neutrons have no charge, the alpha particle's total charge comes from its two protons, making it \( +2e \).

🎯 Exam Tip: Clearly state that an alpha particle is a doubly ionized helium nucleus, explaining its \( +2e \) charge.

 

Question 15. Which of the following has speed from 1/10 to 1/20 times the speed of light?
(a) \( \beta \)
(b) \( \alpha \)
(c) \( \gamma \)
(d) All the options
Answer: (b) \( \alpha \)
In simple words: Alpha particles are relatively heavy, so they travel at speeds between one-tenth and one-twentieth the speed of light. Beta particles are faster, and gamma rays travel at the speed of light.

🎯 Exam Tip: Remember that the speed of radioactive particles is inversely related to their mass; heavier alpha particles are slower compared to lighter beta particles and massless gamma rays.

 

Question 16. In \( \alpha \) - decay _____.
(a) atomic number decreases by 2 and the mass number decreases by 4
(b) atomic number increases by 2 and the mass number decreases by 4
(c) there is no change in atomic and mass number
(d) neutron number decreases by one.
Answer: (a) atomic number decreases by 2 and the mass number decreases by 4
In simple words: When an atom undergoes alpha decay, it releases an alpha particle (two protons and two neutrons). This causes its atomic number to go down by 2 and its mass number to go down by 4.

🎯 Exam Tip: Always link alpha decay to the emission of a helium nucleus (\( _{2}He^{4} \)), which explains the specific changes in atomic and mass numbers.

 

Question 17. Which of the following is a fertile material?
(a) Thorium - 232
(b) Uranium - 238
(c) Plutonium - 240
(d) All of the options
Answer: (d) All of the options
In simple words: Thorium-232, Uranium-238, and Plutonium-240 are all examples of fertile materials. These are materials that can be converted into fissile materials (which can sustain a nuclear chain reaction) through neutron absorption.

🎯 Exam Tip: Differentiate fertile materials (can become fissile) from fissile materials (can sustain a chain reaction directly).

 

Question 18. If the mass of the fissile material is less than the critical mass, then it is termed as:
(a) supercritical
(b) critical
(c) subcritical
(d) None of the options
Answer: (c) subcritical
In simple words: When a fissile material's mass is smaller than its critical mass, it is called subcritical. In this state, a chain reaction cannot be sustained because too many neutrons escape, and not enough fission events happen.

🎯 Exam Tip: Understand the three states: subcritical (reaction dies out), critical (sustained reaction), and supercritical (exponentially growing reaction).

 

Question 19. 1 curie is equal to _____.
(a) the radioactivity of 1 gram of uranium
(b) 1 decay/second
(c) \( 3.7 \times 10^{10} \) becquerel
(d) \( 1.6 \times 10^{12} \) decay / second.
Answer: (c) \( 3.7 \times 10^{10} \) becquerel
In simple words: The unit 'curie' measures radioactivity, and one curie is exactly equal to \( 3.7 \times 10^{10} \) nuclear disintegrations per second, which is the definition of a becquerel.

🎯 Exam Tip: Memorize the conversion factor between curie and becquerel, as it's a common conversion in radioactivity calculations.

 

Question 20. During nuclear fusion which of the following are emitted:
(a) alpha rays
(b) positrons
(c) neutrons
(d) All of the options
Answer: (d) All of the options
In simple words: Nuclear fusion, which powers stars, can emit various particles depending on the specific reaction. These can include alpha particles, positrons, and neutrons, making the answer "all of the options."

🎯 Exam Tip: While energy is the primary product, be aware that fusion reactions can also release subatomic particles, depending on the reactants and products.

 

Question 21. Anaemia can be diagnosed by:
(a) \( _{11}Na^{24} \)
(b) \( _{26}Fe^{59} \)
(c) \( _{11}Na^{24} \)
(d) \( _{28}Fe^{59} \)
Answer: (b) \( _{26}Fe^{59} \)
In simple words: Radioactive Iron-59 (\( _{26}Fe^{59} \)) is used in medicine to track iron absorption in the body, which helps diagnose anaemia (iron deficiency). This isotope allows doctors to see how well the body is using iron.

🎯 Exam Tip: Link specific radioisotopes to their medical applications; for anaemia, \( _{26}Fe^{59} \) is a key diagnostic tool.

 

Question 23. In which decay atomic number of daughter element is increased by 1 unit?
(a) \( \alpha \) – decay
(b) \( \beta \) – decay
(c) \( \gamma \) decay
(d) neutron decay
Answer: (b) \( \beta \) – decay
In simple words: Beta decay increases the atomic number by one, meaning the daughter element moves one spot higher on the periodic table. This happens because a neutron changes into a proton, releasing an electron.

🎯 Exam Tip: Remember that in beta decay, the mass number stays the same, but the atomic number increases, while in alpha decay, both decrease.

 

Question 24. in nuclear fusion __________ is satisfied.
(a) law of conservation of energy
(b) law of conservation of momentum
(c) law of conservation of angular momentum
(d) mass energy relation
Answer: (d) mass energy relation
In simple words: Nuclear fusion reactions follow Einstein's mass-energy relation, where a small amount of mass is converted into a large amount of energy. This means the total energy and momentum are conserved, but the mass and energy are directly related and can change forms.

🎯 Exam Tip: Nuclear reactions always follow the principle of mass-energy equivalence, meaning mass can be converted into energy and vice-versa, as described by Einstein's famous equation \(E=mc^2\).

 

Question 25. The safe limit of receiving the radiation is about __________.
(a) 100 R
(b) 600 R
(c) 250 R
(d) 250 mR per week.
Answer: (d) 250 mR per week.
In simple words: The maximum amount of radiation a person can safely receive in one week is 250 milliroentgens. Going over this limit can be harmful to health.

🎯 Exam Tip: Always be aware of safe radiation limits in specific units (like mR or sieverts) and consider both acute and cumulative exposure for safety protocols.

 

Question 26. Hydrogen bomb is based on the principle of:
(a) natural radioactivity
(b) induced radioactivity
(c) nuclear fusion
(d) nuclear fission
Answer: (c) nuclear fusion
In simple words: Hydrogen bombs work by forcing light atomic nuclei to join together, which is called nuclear fusion. This process releases a huge amount of energy, much like what happens in the sun.

🎯 Exam Tip: Distinguish between nuclear fission (splitting atoms, used in atomic bombs and power plants) and nuclear fusion (combining atoms, used in hydrogen bombs and stars).

 

Question 27. Uncontrolled chain reaction yields __________
(a) nuclear reactor
(b) atom bomb
(c) hydrogen bomb
(d) breeder reactor.
Answer: (b) atom bomb
In simple words: An uncontrolled chain reaction, where neutrons keep splitting atoms very quickly without being slowed down, is the basic principle behind how an atom bomb explodes. This rapid chain reaction releases an immense amount of energy very suddenly.

🎯 Exam Tip: Uncontrolled chain reactions are highly destructive, while controlled chain reactions are harnessed for power generation in nuclear reactors.

 

Question 28. In the following reaction. \( _{1}H^3 + _{1}H^2 \rightarrow X + Y + \text{energy} \) X and Y are:
(a) \( _{2}He^3, _{0}n^1 \)
(b) \( _{2}He^4, _{0}n^1 \)
(c) \( _{1}H^2, _{0}n^1 \)
(d) \( _{1}H^3, _{0}n^1 \)
Answer: (b) \( _{2}He^4, _{0}n^1 \)
In simple words: When tritium (\( _{1}H^3 \)) and deuterium (\( _{1}H^2 \)) combine, they form a helium nucleus (\( _{2}He^4 \)) and a neutron (\( _{0}n^1 \)), releasing a lot of energy. This process is nuclear fusion.

🎯 Exam Tip: In nuclear reactions, always ensure that the total atomic number (Z) and total mass number (A) are conserved on both sides of the equation.

 

Question 29. The number of \( \alpha \) and \( \beta \) particles emitted when \( _{92}U^{238} \) decays to \( _{82}Pb^{206} \) are respectively:
(a) 6, 8
(b) 8, 6
(c) 4, 3
(d) 3, 4
Answer: (b) 8, 6
In simple words: To change Uranium-238 into Lead-206, the original atom must release 8 alpha particles and 6 beta particles. This happens through a series of steps to reduce the mass and atomic numbers to the final values.

🎯 Exam Tip: For alpha decay, mass number decreases by 4, atomic number by 2. For beta decay, mass number stays the same, atomic number increases by 1. Use these rules to calculate the number of decays needed.

 

Question 30. The fusion process can be carried out only at a temperature of __________.
(a) 1000°C
(b) 100°C
(c) 104°C
(d) 10\(^7\) K.
Answer: (d) 10\(^7\) K.
In simple words: Nuclear fusion reactions need extremely high temperatures, around ten million Kelvin, to happen. This is because the atomic nuclei need a lot of energy to overcome their natural repulsion and join together.

🎯 Exam Tip: Fusion requires immense temperatures and pressures, similar to those found in the core of stars, making it challenging to achieve on Earth.

 

Question 31. Which of the following is used to cure goiter?
(a) \( _{11}Na^{24} \)
(b) \( I^{131} \)
(c) \( P^{32} \)
(d) \( Fe^{59} \)
Answer: (b) \( I^{131} \)
In simple words: Radioactive Iodine-131 is used to treat goiter, a condition where the thyroid gland is enlarged. The thyroid gland absorbs iodine, so the radioactive version helps to reduce its size.

🎯 Exam Tip: Know the specific medical applications of common radioisotopes, as they are frequently tested.

 

Question 32. Which radio isotope is used to check the function of heart?
(a) \( Na^{24} \)
(b) \( Fe^{59} \)
(c) \( Co^{60} \)
(d) \( I^{131} \)
Answer: (a) \( Na^{24} \)
In simple words: Radioactive Sodium-24 is used by doctors to check how well the heart is working. It helps them see blood flow and find any problems.

🎯 Exam Tip: Remember that different radioisotopes have specific uses in medicine, often related to how the body processes the non-radioactive version of that element.

 

Question 33. The fuel of the prototype fast breeder reactor is __________.
(a) low enriched uranium
(b) carbides of uranium
(c) high enriched uranium
(d) oxides of plutonium and uranium.
Answer: (d) oxides of plutonium and uranium.
In simple words: Fast breeder reactors primarily use a mix of plutonium and uranium oxides as their fuel. This specific fuel allows them to produce more fissile material than they consume.

🎯 Exam Tip: Fast breeder reactors are unique because they can generate new fuel (like plutonium-239) from non-fissile materials (like uranium-238) while producing power.

 

Question 34. Which radio isotope is used as a smoke detector?
(a) \( Cf^{232} \)
(b) \( I^{131} \)
(c) \( Na^{24} \)
(d) \( Am^{241} \)
Answer: (d) \( Am^{241} \)
In simple words: Americium-241 is a radioactive material commonly found in many household smoke detectors. It emits alpha particles, which helps the detector sense smoke.

🎯 Exam Tip: Know that Americium-241 is an alpha emitter, and its alpha particles are crucial for the ionization chamber function in smoke detectors.

 

Question 35. The control rod used in a nuclear reactor is __________.
(a) barium
(b) carbon
(c) cadmium
(d) Na.
Answer: (c) cadmium
In simple words: Cadmium is a material used in nuclear reactors to make control rods. These rods help to slow down or stop the nuclear reaction by absorbing extra neutrons.

🎯 Exam Tip: Control rods are essential for safely operating nuclear reactors by regulating the rate of the chain reaction through neutron absorption.

 

II. Fill in the blanks.

 

Question 1. Radium was discovered by __________.
Answer: Marie Curie and Pierre Curie
In simple words: Radium was found by the scientists Marie and Pierre Curie. They worked together to identify this new element.

🎯 Exam Tip: Remember the key figures in the discovery of radioactivity and new radioactive elements.

 

Question 2. The __________ effect is an instantaneous process Natural radioactivity is a __________.
Answer: photoelectric, spontaneous
In simple words: The photoelectric effect happens instantly. Natural radioactivity is a process that occurs on its own.

🎯 Exam Tip: Differentiate between processes that require external energy (like photoelectric effect) and those that occur naturally (like spontaneous radioactivity).

 

Question 3. The elements with atomic number __________ undergo spontaneous radioactivity.
Answer: more than 83
In simple words: Elements that have an atomic number greater than 83 naturally give off radiation. This means they are unstable and decay on their own.

🎯 Exam Tip: The stability of a nucleus generally decreases with increasing atomic number, with elements above bismuth (atomic number 83) typically being radioactive.

 

Question 4. In natural radioactivity emission of radiation is due to __________ of a nucleus.
Answer: self-disintegration
In simple words: When a nucleus breaks apart by itself, it releases radiation. This breaking apart is called self-disintegration and is why natural radioactivity happens.

🎯 Exam Tip: Natural radioactivity is a spontaneous process where unstable nuclei decay, emitting particles and energy to become more stable.

 

Question 5. One disintegration per second is equal to __________.
Answer: Becquerel
In simple words: When one atomic nucleus breaks down in one second, that amount of radioactivity is called one Becquerel. It's a way to measure how active a radioactive substance is.

🎯 Exam Tip: Becquerel (Bq) is the SI unit for activity, representing one disintegration per second, while Curie (Ci) is a much larger, older unit.

 

Question 6. S.I unit of radioactivity is __________.
Answer: Becquerel
In simple words: The standard scientific unit for measuring radioactivity is the Becquerel. It tells us how many atomic decays happen each second.

🎯 Exam Tip: The Becquerel (Bq) is the official SI unit, but Curie (Ci) is also commonly used, especially in older texts and medical contexts.

 

Question 7. The speed of __________ can go upto 9/10 times the velocity of light.
Answer: \( \beta \) rays
In simple words: Beta rays can travel very fast, almost as fast as light itself. Their speed can be up to 9/10ths of the speed of light.

🎯 Exam Tip: Beta particles (electrons) are much lighter than alpha particles, allowing them to achieve much higher speeds.

 

Question 8. \( \alpha \) ray is __________.
Answer: a helium nucleus
In simple words: An alpha ray is actually a helium nucleus. It is made up of two protons and two neutrons, and it has a positive charge.

🎯 Exam Tip: Remember that an alpha particle is equivalent to a \( _{2}He^4 \) nucleus, meaning it has a mass number of 4 and an atomic number of 2.

 

Question 9. __________ ray consists of photons.
Answer: Gamma
In simple words: Gamma rays are made of tiny packets of energy called photons. They are a form of light that we cannot see.

🎯 Exam Tip: Gamma rays are electromagnetic radiation, not particles like alpha or beta, and are therefore made of photons and have no mass or charge.

 

Question 10. __________ and __________ are deflected by electric and magnetic fields.
Answer: Alpha, beta
In simple words: Both alpha and beta particles have an electric charge, so they bend when they pass through electric or magnetic fields. Gamma rays do not bend because they have no charge.

🎯 Exam Tip: Charged particles (alpha positive, beta negative) are deflected by fields, while neutral particles (gamma) are not.

 

Question 11. When uranium decays into thorium __________ particle is emitted.
Answer: alpha
In simple words: When uranium atoms break down to become thorium, they release alpha particles. This is a type of natural decay.

🎯 Exam Tip: The decay of Uranium-238 to Thorium-234 is a classic example of alpha decay, where the mass number decreases by 4 and the atomic number by 2.

 

Question 12. In __________ decay there is no change in the mass number of the product.
Answer: beta
In simple words: During beta decay, the mass of the atomic nucleus stays the same, even though its atomic number changes. This is because a neutron turns into a proton, emitting an electron.

🎯 Exam Tip: Beta decay involves the transformation of a neutron into a proton (or vice versa), which changes the atomic number but not the total number of nucleons (mass number).

 

Question 13. The minimum mass of a fissile material necessary to sustain the chain reaction is called __________.
Answer: critical mass
In simple words: The smallest amount of fissile material needed for a nuclear chain reaction to keep going on its own is known as critical mass. If there's less than this, the reaction will stop.

🎯 Exam Tip: Critical mass is a key concept in nuclear fission, determining whether a chain reaction is sustained (critical), dies out (subcritical), or grows uncontrollably (supercritical).

 

Question 14. The value of 1MeV in joules is __________.
Answer: \( 1.602 \times 10^{-13} \text{ J} \)
In simple words: One Mega-electron Volt (1 MeV) is equal to 1.602 multiplied by ten to the power of minus thirteen Joules. This converts energy from atomic scale units to standard energy units.

🎯 Exam Tip: Remember energy conversion factors, especially between electron volts (eV), mega-electron volts (MeV), and joules (J), as they are fundamental in nuclear physics calculations.

 

Question 15. In the transformation \( _{1}H^2 + _{1}H^2 \rightarrow X + \text{energy} \). X is __________.
Answer: \( _{2}He^4 \)
In simple words: When two deuterium atoms (\( _{1}H^2 \)) combine, they form a helium nucleus (\( _{2}He^4 \)) and release energy. This is a nuclear fusion reaction.

🎯 Exam Tip: Pay attention to the conservation of mass number and atomic number in nuclear reaction equations to identify unknown particles.

 

Question 16. Einstein's mass energy relation is __________.
Answer: \( E=mc^2 \)
In simple words: Einstein's famous formula, \( E=mc^2 \), shows that energy (E) is equal to mass (m) multiplied by the speed of light squared (c\(^2\)). This means mass and energy are two forms of the same thing.

🎯 Exam Tip: This equation is central to understanding energy release in nuclear reactions, where a small amount of mass loss results in a huge amount of energy.

 

Question 17. __________ causes the mutation in the human gene.
Answer: Gamma radiation
In simple words: Gamma radiation can change the genetic material inside human cells, which can lead to mutations. These changes might cause diseases or be passed down to children.

🎯 Exam Tip: High-energy radiation, like gamma rays, can damage DNA, leading to genetic mutations and increased risk of cancer.

 

Question 18. __________ is also used in treatment of skin cancer.
Answer: Radio-gold Au\(^{198}\)
In simple words: Radioactive gold, specifically Au-198, is used to treat skin cancer. Its radiation helps destroy cancer cells.

🎯 Exam Tip: Radioisotopes are crucial in medical therapy, using targeted radiation to destroy cancerous cells while minimizing harm to healthy tissue.

 

Question 19. The safe limit for receiving the radiation is __________.
Answer: 100 mR per week
In simple words: The safe amount of radiation a person can be exposed to is 100 milliroentgens each week. Staying within this limit helps prevent harm from radiation.

🎯 Exam Tip: Radiation safety limits are set to protect individuals from the harmful effects of ionizing radiation, with specific limits for occupational and public exposure.

 

Question 20. The substances that are used as coolants are __________ and __________.
Answer: Water, air and helium
In simple words: Water, air, and helium are commonly used to cool down nuclear reactors. They carry away the heat produced during the nuclear reactions.

🎯 Exam Tip: Coolants in nuclear reactors prevent overheating and transfer heat to generate electricity; their choice depends on reactor design and safety requirements.

 

Question 21. __________ reactors convert non-fissionable material units.
Answer: Breeder
In simple words: Breeder reactors have a special ability to turn materials that can't be split (non-fissionable) into ones that can (fissionable). This helps create more fuel.

🎯 Exam Tip: Breeder reactors are important for sustainable nuclear energy because they can produce more fissile material than they consume, effectively "breeding" new fuel.

 

Question 22. The expansion of BARC is __________.
Answer: Bhabha Atomic Research Centre
In simple words: BARC stands for Bhabha Atomic Research Centre. It is a big science center in India that works on atomic energy and related research.

🎯 Exam Tip: Knowing the full forms of important scientific organizations shows a good general understanding of the field.

 

Question 23. The number of nuclear reactor that are operating in India are __________.
Answer: 22
In simple words: India currently has 22 nuclear reactors that are producing electricity. These reactors are spread across various power stations.

🎯 Exam Tip: Keep up-to-date with current events and facts related to national energy infrastructure, as these can appear in general knowledge questions.

 

Question 24. Identify X in the following transformation \( _{12}Mg^{24} + _{0}n^1 \rightarrow _{11}Na^{24} + X \). X is __________.
Answer: \( _{1}H^1 \)
In simple words: In this nuclear reaction, when Magnesium-24 is hit by a neutron, it turns into Sodium-24. The extra particle (X) that is released must be a proton (\( _{1}H^1 \)) to balance the numbers.

🎯 Exam Tip: For nuclear reactions, balance both the mass numbers (superscripts) and atomic numbers (subscripts) on both sides of the equation to identify unknown particles.

 

Question 25. In the reaction \( _{92}U^{238} + _{0}n^1 \rightarrow _{93}Np^{239} + X \). X is __________.
Answer: \( _{-1}e^0 \)
In simple words: When Uranium-238 absorbs a neutron and becomes Neptunium-239, an electron (\( _{-1}e^0 \)) is released. This process is a type of beta decay.

🎯 Exam Tip: Remember that a neutron undergoing beta decay (transforming into a proton and electron) results in the atomic number increasing by 1 while the mass number remains unchanged.

 

III. State whether the following statements are true or false: If false, correct the statement.

 

Question 1. Artificial radioactivity is induced in the elements like boron, aluminum etc.
Answer: True
In simple words: It is true that we can make elements like boron and aluminum radioactive artificially. This is done by hitting them with certain particles.

🎯 Exam Tip: Artificial radioactivity, also known as induced radioactivity, is created by bombarding stable nuclei with high-energy particles to make them unstable and radioactive.

 

Question 2. Natural radioactivity can be controlled.
Answer: False – Artificial radio activity can be controlled.
In simple words: Natural radioactivity cannot be controlled, it happens on its own. Only artificial radioactivity, which humans create, can be managed.

🎯 Exam Tip: The spontaneous nature of natural radioactivity means it cannot be sped up, slowed down, or stopped by external means like temperature or pressure.

 

Question 3. 1 Rd = \( 3.7 \times 10^{10} \) disintegrations / second.
Answer: False – 1 curie = \( 3.7 \times 10^{10} \) disintegrations / second.
In simple words: The statement is wrong. One curie, not one Rutherford (Rd), is equal to 3.7 times ten to the power of ten disintegrations per second. One Rutherford is \( 10^6 \) disintegrations per second.

🎯 Exam Tip: Be careful with the units of radioactivity; 1 Curie is a much larger unit than 1 Rutherford or 1 Becquerel.

 

Question 4. The S.I unit of radioactivity is roentgen.
Answer: False – The S.I unit of radioactivity is Becquerel.
In simple words: The correct SI unit for radioactivity is Becquerel. Roentgen is a unit for measuring exposure to X-rays and gamma rays, not the activity itself.

🎯 Exam Tip: Differentiate between the units of radioactivity (Becquerel, Curie, Rutherford) and radiation exposure (Roentgen) or absorbed dose (Gray, Rad).

 

Question 5. The charge of each beta particle is \( -e \).
Answer: True
In simple words: It is correct that each beta particle carries a negative charge, which is equal to the charge of an electron.

🎯 Exam Tip: Remember the charges of common particles: alpha (+2e), beta (-e), gamma (0), proton (+e), electron (-e), neutron (0).

 

Question 6. Beta ray travels with velocity of light.
Answer: False - Gamma ray travels with velocity of light.
In simple words: Beta rays travel very fast, but not exactly at the speed of light. Gamma rays, which are a form of light, are the ones that travel at the speed of light.

🎯 Exam Tip: Only electromagnetic waves (like gamma rays and visible light) travel at the speed of light in a vacuum; particles (like alpha and beta) travel at speeds approaching, but not equal to, the speed of light.

 

Question 7. Example for alpha decay is \( _{92}U^{238} \rightarrow _{90}Th^{234} + _{2}He^4 \).
Answer: True
In simple words: This statement is true. Uranium-238 decaying into Thorium-234 by releasing an alpha particle is a perfect example of alpha decay.

🎯 Exam Tip: Recognize common examples of alpha decay, where a heavy nucleus emits a helium nucleus (alpha particle), reducing its mass by 4 and atomic number by 2.

 

Question 8. Otto Hann and Strassman discovered nuclear fission.
Answer: True
In simple words: It is true that Otto Hahn and Fritz Strassmann were the scientists who discovered nuclear fission. They found out that atomic nuclei could be split.

🎯 Exam Tip: Associate key discoveries with their scientists; Hahn and Strassmann are credited with the experimental discovery of nuclear fission.

 

Question 9. In the mass of the fissile material is more than the critical mass it is termed supercritical.
Answer: True
In simple words: If a fissile material has more mass than its critical mass, it is called supercritical. This means a nuclear chain reaction will grow very quickly.

🎯 Exam Tip: Understand the three states of criticality: subcritical (reaction dies out), critical (sustained reaction), and supercritical (rapidly increasing reaction).

 

Question 10. Hydrogen bomb is based on uncontrolled chain reaction.
Answer: False – Atom bomb is based on uncontrolled chain reaction.
In simple words: This is false. An atom bomb uses an uncontrolled chain reaction (fission). A hydrogen bomb uses nuclear fusion, which also releases energy in an uncontrolled way, but it's a different type of reaction.

🎯 Exam Tip: The distinction between fission (atom bomb) and fusion (hydrogen bomb) principles is crucial, though both can involve uncontrolled energy release.

 

Question 11. 1eV = \( 1.602 \times 10^{-16} \) Joule.
Answer: False – 1eV = \( 1.602 \times 10^{-19} \) Joule
In simple words: The statement is incorrect. One electron volt (1 eV) is equal to 1.602 multiplied by ten to the power of minus nineteen Joules, not minus sixteen.

🎯 Exam Tip: Memorize the conversion factor between electron-volts and joules, as it's fundamental for energy calculations in atomic and nuclear physics.

 

Question 12. Hydrogen is based on nuclear fusion.
Answer: True
In simple words: It is true that a hydrogen bomb works by combining light atomic nuclei, a process known as nuclear fusion.

🎯 Exam Tip: Reinforce the understanding that hydrogen bombs derive their energy from nuclear fusion, typically involving isotopes of hydrogen.

 

Question 13. Positrons are emitted in nuclear fusion.
Answer: True
In simple words: Positrons are indeed given off during nuclear fusion. They are an anti-matter equivalent of electrons and are part of the energy release.

🎯 Exam Tip: Positron emission (a type of beta decay) can occur in fusion reactions as protons convert to neutrons, especially in stars.

 

Question 14. To diagnose anaemia P\(^{32}\) is used.
Answer: False – To diagnose anaemia Fe\(^{59}\) is used.
In simple words: This is false. Iron-59 is used to find and understand anaemia. Phosphorus-32 is used for other purposes, like treating skin diseases.

🎯 Exam Tip: Accurately matching radioisotopes with their specific medical diagnostic or treatment uses is important. Iron is key for blood, thus Fe-59 for anaemia.

 

Question 15. Radio phosphorous is used in the treatment of skin diseases.
Answer: True
In simple words: It is true that radioactive phosphorus is used to treat some skin diseases. Its radiation helps in targeting and affecting diseased cells.

🎯 Exam Tip: Phosphorous-32 is a beta emitter, and its beta particles can be used for shallow tissue treatment, making it suitable for certain skin conditions.

 

IV. Match the following.

 

Question 1. Match the Column I with Column II.

Answer:
(a) – (iii)
(b) – (iv)
(c) – (v)
(d) – (i)
In simple words: Curie is a unit equal to 3.7 x 10\(^{10}\) disintegrations per second. Becquerel is 1 disintegration per second. Rutherford is 10\(^6\) disintegrations per second. Artificial radioactivity is a process that is induced or started by humans.

🎯 Exam Tip: Clearly know the definitions and values for different units of radioactivity, as well as the types of radioactivity (natural vs. artificial).

 

Question 2. Match the Column I with Column II.

Answer:
(a) – (iv)
(b) – (v)
(c) – (ii)
(d) – (i)
In simple words: An alpha ray is a helium nucleus. A beta ray is an electron. Plutonium is a fissile material that can be split. A gamma ray is a type of electromagnetic wave.

🎯 Exam Tip: Understand the nature of different radiations (alpha as helium nucleus, beta as electron, gamma as electromagnetic wave) and common fissile materials.

 

Question 3. Match the Column I with Column II.

Answer:
(a) – (v)
(b) – (iv)
(c) – (i)
(d) – (iii)
In simple words: Radioactive phosphorus is used to treat skin diseases. Radioactive iron is used to diagnose anaemia. Radioactive iodine helps cure goiter. Radioactive cobalt is used in treating heart cancer.

🎯 Exam Tip: Knowing the specific medical applications of various radioisotopes is important for questions on the uses of radioactivity.

 

V. Numerical problems.

 

Question 1. A radioactive isotope emits radiation of \( 7.4 \times 10^4 \text{ G Bq} \) per second. Convert this disintegration in terms of curie.
Answer:
One curie \( = 3.7 \times 10^{10} \) Becquerel
Becquerel \( (1 \text{ Bq}) = \) One disintegration / second
\( \implies 1 \text{ Bq} = \frac{1}{3.7 \times 10^{10}} \) curie
So, \( 7.4 \times 10^4 \text{ G Bq} \)
\( = 7.4 \times 10^4 \times 10^9 \times \frac{1}{3.7 \times 10^{10}} \)
\( = 2 \times 10^3 \) curie
\( = 2,000 \) curie
In simple words: To change a very high Becquerel value into Curie, you divide by the number that defines one Curie. Here, we converted Giga Becquerel to Becquerel first, then to Curie, which resulted in 2000 curies.

🎯 Exam Tip: Always pay attention to unit conversions (Giga-Becquerel to Becquerel, then Becquerel to Curie) and use the correct conversion factors in numerical problems.

 

Question 2. The isotope \( _{92}U^{238} \) successfully undergoes three \( \alpha \) – decays and two \( \beta \) – decays. What is the resulting isotope?
Answer:
Atomic number of isotope is \( Z = 92 \)
Mass number of isotope is \( A = 238 \)
Resulting isotope:
After the emission of 3\( \alpha \) particles atomic number
\( Z' = Z - (3 \times 2) \)
\( = Z - 6 \)
\( = 92 - 6 \)
\( = 86 \)
After the emission of 2\( \beta \) particles atomic number
\( Z'' = Z' - 2(-1) = 86 + 2 = 88 \)
Mass number after the emission of 3\( \alpha \) particles
\( A' = A - 3\alpha \)
\( = 238 - 3(4) \)
\( = 238 - 12 \)
\( = 226 \)
Mass number after the emission of 2\( \beta \) particles
\( A'' = A' - 2(0) \)
\( = 226 \)
\( \implies \) Resulting isotope is \( _{88}Ra^{226} \)
In simple words: When Uranium-238 loses three alpha particles, its atomic number goes down by 6 and its mass number by 12. Then, losing two beta particles increases the atomic number by 2, but the mass number stays the same. The final element is Radium-226.

🎯 Exam Tip: Systematically apply the changes to atomic number (Z) and mass number (A) for each alpha (Z-2, A-4) and beta (Z+1, A-0) decay step to find the final isotope.

 

Question 3. \( _{88}Ra^{226} \) experiences one \( \alpha \) – decay and one \( \beta \) – decay. Calculate the number of neutrons in the final daughter nucleus that is formed.
Answer:
\( \alpha \) particle \( = _{2}He^4 \)
Atomic number of \( \alpha \) particle \( = 2 \)
Mass number of \( \alpha \) particle \( = 4 \)
\( _{88}Ra^{226} \stackrel{\alpha \text{ decay}}{\longrightarrow} _{86}X^{222} + _{2}He^4 \)
\( _{86}X^{222} \stackrel{\beta \text{ decay}}{\longrightarrow} _{87}Y^{222} + _{-1}e^0 \)
Number of neutrons \( = \) Mass number \( - \) atomic number
\( = 222 - 87 = 135 \)
In simple words: First, Radium-226 emits an alpha particle, becoming an element with atomic number 86 and mass 222. Then, this new element emits a beta particle, becoming an element with atomic number 87 and still mass 222. To find the neutrons, subtract the atomic number (87) from the mass number (222), which gives 135 neutrons.

🎯 Exam Tip: Remember to calculate the atomic and mass numbers after each decay step before determining the number of neutrons in the final nucleus.

 

Question 4. State the number of protons, electrons neutrons and nucleons in \( _{4}Be^9 \) atom.
Answer:
Atomic number of \( _{4}Be^9 \) atom \( Z = 4 \)
Mass number of \( _{4}Be^9 \) atom \( A = 9 \)
Number of protons \( = \) Atomic number \( Z = 4 \)
Number of neutrons \( = A - Z = 9 - 4 = 5 \)
Number of nucleons \( = A = 9 \)
In simple words: For a Beryllium-9 atom, it has 4 protons (from its atomic number) and 4 electrons (to be neutral). It has 5 neutrons (mass number 9 minus atomic number 4). The total number of nucleons (protons and neutrons) is 9.

🎯 Exam Tip: Understand that the atomic number (Z) represents protons (and electrons in a neutral atom), the mass number (A) represents total nucleons, and neutrons are found by A-Z.

 

Question 5. Determine X and Y in the following transformations.
(i) \( _{4}Be^9 + \alpha \rightarrow X \)
(ii) \( _{92}U^{235} + _{0}n^1 \rightarrow _{50}Ba^{141} + Y + 3_{0}n^1 \)
Answer:
(i) \( _{4}Be^9 + _{2}He^4 \rightarrow _{6}C^{13} \)
\( \implies X = _{6}C^{13} \)
(ii) \( _{92}U^{235} + _{0}n^1 \rightarrow _{50}Ba^{141} + Y + 3_{0}n^1 \)
Equating atomic number on both sides we get,
\( 92 + 0 = 56 + Z_Y + 3(0) \)
\( 92 = 56 + Z_Y \)
\( \implies Z_Y = 92 - 56 = 36 \)
Equating mass number on both sides we get,
\( 235 + 1 = 141 + A_Y + 3(1) \)
\( 236 = 141 + A_Y + 3 \)
\( 236 = 144 + A_Y \)
\( \implies A_Y = 236 - 144 = 92 \)
\( \implies Y = _{36}Kr^{92} \)
In simple words: For the first reaction, Beryllium-9 absorbs an alpha particle (Helium nucleus) to become Carbon-13 (X). For the second, Uranium-235 absorbs a neutron and splits into Barium-141 and three neutrons. To balance the atomic and mass numbers, the missing element Y must be Krypton-92.

🎯 Exam Tip: For nuclear transformations, ensure both the total mass number (sum of superscripts) and total atomic number (sum of subscripts) are conserved on both sides of the equation.

 

Question 6. Calculate the amount energy released when a radioactive element undergoes fusion and results in a mass defect of 4g.
Answer:
Velocity of light \( = 3 \times 10^8 \text{ m/s} \)
Mass defect \( \Delta m = 4 \times 10^{-3} \text{ kg} \)
By Einstein's equation, energy released:
\( E = \Delta mc^2 \)
\( = (4 \times 10^{-3}) \times (3 \times 10^8)^2 \)
\( = 4 \times 10^{-3} \times 9 \times 10^{16} \)
\( = 36 \times 10^{13} \text{ J} \)
\( = 3.6 \times 10^{14} \text{ J} \)
In simple words: When a radioactive element combines and loses 4 grams of mass, a large amount of energy is released. Using Einstein's formula \( E=mc^2 \), and converting grams to kilograms, the energy released is 3.6 times ten to the power of fourteen Joules. This shows how a small mass change can produce huge energy.

🎯 Exam Tip: When using \( E=mc^2 \), ensure mass is in kilograms (kg) and the speed of light (c) is \( 3 \times 10^8 \text{ m/s} \). Convert units carefully to avoid errors.

 

Question 7. Identify the radio isotopes in the following reactions.
(i) \( _{15}P^{8} + _{0}n^1 \rightarrow X + \gamma \)
(ii) \( _{0}n^1 \rightarrow _{Z}Y^A + _{-1}e^0 + \gamma \)
Answer:
(i) \( _{15}P^{31} + _{0}n^1 \rightarrow _{15}P^{32} + \gamma \)
Mass number of X \( = 31 + 1 = 32 \)
Atomic number of X \( = 15 + 0 = 15 \)
\( \implies X \) is \( _{15}P^{32} \)
(ii) \( _{0}n^1 \rightarrow _{1}H^1 + _{-1}e^0 + \gamma \)
Mass number \( A = 1 \)
Atomic number \( Z = 1 \)
\( \implies Y \) is \( _{1}H^1 \)
In simple words: In the first reaction, Phosphorus-31 absorbs a neutron to become Phosphorus-32 (X), releasing a gamma ray. In the second, a neutron decays to become a proton (Y), an electron, and a gamma ray. The radioactive isotopes identified are Phosphorus-32 and Hydrogen-1 (proton).

🎯 Exam Tip: Always balance both the mass number (superscript) and atomic number (subscript) on both sides of a nuclear reaction to correctly identify unknown particles or isotopes.

 

VI. Assertion and reason type questions.

 

Question 1. Assertion: Natural radioactivity is a spontaneous process. Reason: It cannot be controlled.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
In simple words: Natural radioactivity happens on its own (it's spontaneous) and cannot be controlled. The fact that it cannot be controlled directly explains why it is a spontaneous process, so both statements are true and the reason is correct.

🎯 Exam Tip: For Assertion-Reason questions, first determine if each statement is true, then check if the reason correctly explains the assertion. A spontaneous process is inherently uncontrollable by external factors.

 

Question 2. Assertion: In artificial radioactivity neutron and positron are emitted. Reason: It can be controlled.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
In simple words: It is true that neutrons and positrons can be released in artificial radioactivity, and it is also true that artificial radioactivity can be controlled. However, the ability to control it does not explain *why* neutrons and positrons are emitted. These are separate facts.

🎯 Exam Tip: Even if both statements are true, the reason must logically explain *why* the assertion is true for option (a) to be correct. If they are just two unrelated true facts, choose (b).

 

Question 3. Assertion: p rays are electrons. Reason: p rays travel with speed of light.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (c) If the assertion is true, but the reason is false.
In simple words: This answer suggests that beta rays (often mistaken for p-rays in some contexts) are electrons, which is true. However, beta rays do not travel at the speed of light, making the reason false.

🎯 Exam Tip: Remember that "p-rays" or "positive rays" are streams of positively charged ions, typically protons (like hydrogen nuclei), not electrons. However, in some contexts, a typo might occur for beta (β) rays, which are indeed electrons.

 

Question 4. Assertion: Gamma rays have maximum ionising power. Reason: Alpha rays have low penetrating power.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (d) If the assertion is false, but the reason is true.
In simple words: Gamma rays actually have the least power to ionize atoms, while alpha rays have the most. However, alpha rays are indeed known for having very low penetrating power, meaning they cannot travel far through materials.

🎯 Exam Tip: Keep the properties of alpha, beta, and gamma radiations clear: alpha has high ionizing power but low penetrating power, while gamma has low ionizing power but very high penetrating power.

 

Question 5. Assertion: Critical mass of a fissile material is the mass necessary to sustain chain reaction. Reason: It depends on the nature, density and size of the fissile material.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
In simple words: Critical mass is indeed the minimum amount of material needed to keep a chain reaction going. This exact amount changes depending on what the material is made of, how dense it is, and its shape and size.

🎯 Exam Tip: Understand that critical mass is a specific threshold. While the properties of the material influence this threshold, stating those dependencies does not explain *why* critical mass is necessary for a chain reaction in the first place.

 

Question 6. Assertion: Nuclear fusion takes place in the cores of the sun and other stars. Reason: Nuclear fusion is called as thermonuclear reaction.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
In simple words: Nuclear fusion, which needs very high heat, occurs naturally in the sun and stars. This is why it is also known as a thermonuclear reaction, meaning a reaction driven by high temperatures.

🎯 Exam Tip: Always link 'thermonuclear' to the extreme temperatures required for fusion reactions, like those found in stellar cores.

 

Question 7. Assertion: An alpha particle carries double the positive charge of protons. Reason: The charge of alpha particle is equal to charge on the helium nucleus.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
In simple words: An alpha particle is made of two protons and two neutrons, just like a helium nucleus. So, it carries twice the positive charge of a single proton. The reason given simply states what an alpha particle is, not why it has that specific charge.

🎯 Exam Tip: Remember that an alpha particle is identical to a helium nucleus \( (\text{He}^{2+}) \), which has an atomic number of 2, thus carrying \( +2e \) charge.

 

Question 8. Assertion: Gamma rays are electromagnetic waves. Reason: Gamma rays travel with speed of light.
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
(c) If the assertion is true, but the reason is false.
(d) If the assertion is false, but the reason is true.
Answer: (a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
In simple words: Gamma rays are a type of electromagnetic wave, which means they are pure energy and have no mass. All electromagnetic waves, including gamma rays, travel at the speed of light in a vacuum.

🎯 Exam Tip: Understand that gamma rays are high-energy photons, belonging to the same family as visible light, radio waves, and X-rays, all of which share the characteristic of traveling at the speed of light.

VII. Answer in one or two words (VSA).

 

Question 1. Who discovered the nucleus?
Answer: Ernest Rutherford.
In simple words: Ernest Rutherford discovered the nucleus through his famous gold foil experiment, where alpha particles were scattered.

🎯 Exam Tip: Associate Rutherford with the nuclear model of the atom and the discovery of the nucleus, as well as the gold foil experiment.

 

Question 2. Define 'Natural Radioactivity'.
Answer: Natural radioactivity is the spontaneous emission of radiation (like alpha, beta, and gamma rays) from the unstable nuclei of certain elements without any external influence.
In simple words: It's when certain elements give off radiation all by themselves, without anyone doing anything to them.

🎯 Exam Tip: The key words here are "spontaneous emission" and "unstable nuclei" for natural radioactivity. Also mention "without external influence."

 

Question 3. State elements exhibiting radioactivity with atomic number less than 83.
Answer: Uranium and radium.
In simple words: These are elements like uranium and radium that are naturally radioactive. Most elements with a very high atomic number are naturally radioactive.

🎯 Exam Tip: While natural radioactivity is commonly associated with elements having an atomic number greater than 82, it's good to know specific examples like Uranium and Radium.

 

Question 4. What is the nature of radioactive substances?
Answer: Radioactive substances are typically heavy elements, often found among earth metals and transition metals.
In simple words: These are usually heavy types of metals, like those found in the earth or in the transition metal group.

🎯 Exam Tip: Remember that the instability leading to radioactivity is often due to a large number of protons and neutrons in the nucleus.

 

Question 5. Define 'One Rutherford (Rd)'.
Answer: One Rutherford (Rd) is a unit of radioactivity defined as the quantity of a radioactive substance that produces \( 10^6 \) disintegrations per second.
In simple words: One Rutherford is a measure of how radioactive something is; it means one million atoms are breaking down every second.

🎯 Exam Tip: The Rutherford unit is a large measure; it is equal to 1 megabecquerel (MBq), emphasizing a high rate of decay.

 

Question 6. In \( _{4}\text{Be}^{9} + _{2}\text{He}^{4} \rightarrow \text{X} \). What is X?
Answer: X is \( _{6}\text{C}^{13} \).
In simple words: When Beryllium-9 combines with an alpha particle (Helium-4), the resulting element, X, is Carbon-13. The atomic numbers (bottom numbers) and mass numbers (top numbers) must add up equally on both sides.

🎯 Exam Tip: In nuclear reactions, remember to conserve both the atomic number (sum of lower numbers) and the mass number (sum of upper numbers) across the reaction arrow.

 

Question 7. What is the value of 1 curie?
Answer: 1 curie is equal to \( 3.7 \times 10^{10} \) disintegrations per second.
In simple words: A curie is a measure of radioactivity, showing that a huge number of atoms are breaking down each second.

🎯 Exam Tip: Note that the Curie is a very large unit of radioactivity, equivalent to 37 gigabecquerels (GBq).

 

Question 8. State the value of Rutherford.
Answer: 1 Rutherford = \( 10^6 \) disintegrations per second.
In simple words: One Rutherford means that a million radioactive atoms are breaking apart every second.

🎯 Exam Tip: The Rutherford unit is often used for describing the activity of laboratory samples, while the Becquerel is the SI unit and the Curie is a much larger historical unit.

 

Question 9. Explain the term 'fissile material' Give an example.
Answer: Fissile material is a radioactive element that can undergo sustained nuclear fission when it absorbs a neutron. It is also known as 'fissionable material'. Examples include Uranium-235 \( (\text{U}^{235}) \) and plutonium \( (\text{Pu}^{239} \) and \( \text{Pu}^{241}) \).
In simple words: A fissile material is a special kind of element that can be easily split apart by neutrons, starting a long chain reaction. Uranium-235 is a good example.

🎯 Exam Tip: Remember that for a material to be fissile, it must be able to sustain a chain reaction, which means it produces more neutrons than it absorbs when it fissions.

 

Question 10. Which ray has greatest ionising power?
Answer: Alpha ray.
In simple words: Alpha rays have the strongest ability to knock electrons off atoms, creating ions.

🎯 Exam Tip: Alpha particles have a relatively large mass and a \( +2 \) charge, which makes them very effective at ionizing atoms but limits their penetrating ability.

 

Question 11. Which ray posses minimum ionising power?
Answer: Gamma ray.
In simple words: Gamma rays have the weakest ability to create ions from atoms because they have no charge and interact less with matter.

🎯 Exam Tip: Gamma rays are electromagnetic radiation (photons) and do not have electric charge, which explains their low ionizing power and high penetrating power.

 

Question 12. Which ray is not deflected by electric and magnetic fields?
Answer: Gamma ray.
In simple words: Gamma rays are not affected by electric or magnetic forces because they do not carry any electric charge.

🎯 Exam Tip: The lack of charge in gamma rays is a key characteristic that distinguishes them from alpha (positive) and beta (negative) particles in electric and magnetic fields.

 

Question 13. Name the ray that travels with speed about 9/10 times that of light?
Answer: Beta ray.
In simple words: Beta rays are very fast-moving electrons that travel at nearly the speed of light.

🎯 Exam Tip: Beta particles are light (electrons), so they can be accelerated to speeds very close to the speed of light, unlike the heavier alpha particles.

 

Question 14. What is the charge of alpha particle?
Answer: Its charge is \( +2e \).
In simple words: An alpha particle has a positive charge that is two times the basic charge of a single electron or proton.

🎯 Exam Tip: The elementary charge 'e' is the magnitude of charge on a single proton or electron. Alpha particles, being helium nuclei, contain two protons.

 

Question 15. Which particle has a charge of -e?
Answer: Beta particle.
In simple words: A beta particle is an electron, which carries a single negative electric charge.

🎯 Exam Tip: Remember that \( -e \) is the charge of an electron, and beta decay involves the emission of an electron (beta particle).

 

Question 16. State that the ray consisting of protons.
Answer: Alpha ray.
In simple words: Alpha rays are made up of helium nuclei, which contain two protons and two neutrons. So, they consist of protons as part of their structure.

🎯 Exam Tip: While alpha rays are not streams of *bare* protons, they are the type of radiation from radioactive decay that contains protons as fundamental components of their nuclei.

 

Question 17. When uranium emits an alpha particle which element is obtained as daughter element.
Answer: Thorium \( _{90}\text{Th}^{234} \).
In simple words: When uranium loses an alpha particle, its nucleus changes, and it becomes thorium. This is because alpha decay reduces the atomic number by two and the mass number by four.

🎯 Exam Tip: For alpha decay, always subtract 4 from the mass number and 2 from the atomic number of the parent nucleus to find the daughter nucleus.

 

Question 18. Mention the value of 1eV in terms of joule.
Answer: \( 1\text{eV} = 1.602 \times 10^{-19} \) joule.
In simple words: An electronvolt is a very small unit of energy, often used in nuclear physics, and it is equal to a tiny fraction of a joule.

🎯 Exam Tip: The electronvolt (eV) is the amount of kinetic energy gained by an electron accelerating through an electric potential difference of 1 volt.

 

Question 19. What is the value of 1MeV?
Answer: \( 1\text{MeV} = 1.602 \times 10^{-13} \) joule.
In simple words: One mega-electronvolt is a million times larger than one electronvolt, representing a significant amount of energy in nuclear processes.

🎯 Exam Tip: Remember that "Mega" (M) means \( 10^6 \), so 1 MeV is \( 10^6 \) times 1 eV, which is \( 10^6 \times 1.602 \times 10^{-19} \) J = \( 1.602 \times 10^{-13} \) J.

 

Question 20. Which radio isotope is used in the treatment of skin diseases?
Answer: Radio Phosphorus \( (\text{P}^{32}) \).
In simple words: A radioactive form of phosphorus is used in medicine to help treat certain skin conditions.

🎯 Exam Tip: Radioisotopes like P-32 are used in medicine because their radiation can target specific cells or tissues, helping to treat various conditions.

 

Question 21. What is the use of radio iodine?
Answer: Radio iodine is used to cure goiter.
In simple words: A radioactive type of iodine is used to treat goiter, a condition that affects the thyroid gland.

🎯 Exam Tip: Radioactive iodine \( (\text{I}^{131}) \) is particularly effective because the thyroid gland naturally absorbs iodine, allowing for targeted treatment.

 

Question 22. Which isotope is used in airlines?
Answer: Californium \( (\text{Cf}^{252}) \) is used in airlines.
In simple words: A special radioactive element called californium is used in the airline industry.

🎯 Exam Tip: Californium-252 is a strong neutron emitter, making it useful in devices that detect explosives in luggage.

 

Question 23. State the isotope used as a smoke detector.
Answer: Americium \( (\text{Am}^{241}) \).
In simple words: A radioactive element named Americium-241 is commonly found in household smoke detectors.

🎯 Exam Tip: Americium-241 emits alpha particles, which ionize the air in the smoke detector, and smoke disrupts this ionization, triggering the alarm.

 

Question 24. Write down the uses of a nuclear reactor.
Answer: Nuclear reactors are used for several important purposes:
1. They generate electricity on a large scale for homes and industries.
2. They produce various radioisotopes, which are vital for medical treatments, industrial applications, and scientific research.
3. Some reactors are dedicated to conducting research in the field of nuclear physics and material science.
In simple words: Nuclear reactors are used to make electricity, create special radioactive materials for many uses, and help scientists study nuclear energy.

🎯 Exam Tip: Focus on the main applications: power generation, radioisotope production, and research, which all stem from controlled nuclear fission.

 

Question 25. What are gamma rays?
Answer: Gamma rays are a type of electromagnetic wave, similar to light or X-rays, and they consist of high-energy packets of energy called photons.
In simple words: Gamma rays are like a super strong form of light, made of pure energy bundles called photons.

🎯 Exam Tip: Remember that gamma rays have no mass and no electric charge, which explains their high penetrating power and low ionizing ability.

 

Question 26. Who discovered Cathode rays.
Answer: J.J. Thomson.
In simple words: J.J. Thomson was the scientist who discovered cathode rays, which are streams of electrons.

🎯 Exam Tip: J.J. Thomson's work with cathode rays was crucial for discovering the electron and developing early models of the atom.

VIII. Answer the following question in few sentences.

 

Question 1. What is radioactivity?
Answer: Radioactivity is a natural process where unstable atomic nuclei spontaneously release energy in the form of radiation (such as alpha, beta, and gamma rays) to become more stable. This release of radiation happens from the nucleus itself.
In simple words: Radioactivity is when unstable atoms give off invisible energy and particles from their center to become more steady.

🎯 Exam Tip: Emphasize the keywords "unstable nuclei," "spontaneous emission," and "radiation" in your definition of radioactivity.

 

Question 2. What is meant by natural radioactivity?
Answer: Natural radioactivity refers to the spontaneous emission of radiation from certain heavy elements (like uranium and radium) that occurs naturally without any human intervention.
In simple words: It's when some elements release radiation on their own, without us doing anything to them, just as they exist in nature.

🎯 Exam Tip: The key difference from artificial radioactivity is the "spontaneous" and "natural occurrence" aspect for elements typically with a high atomic number.

 

Question 3. Define Rutherford.
Answer: The Rutherford (Rd) is a unit of radioactivity. It is defined as the quantity of a radioactive substance that produces \( 10^6 \) disintegrations (nuclear decays) per second.
In simple words: One Rutherford describes a substance that has a million atomic decays happening every second.

🎯 Exam Tip: While Becquerel (Bq) is the SI unit for radioactivity, older units like Rutherford and Curie are still sometimes mentioned. Know their definitions.

 

Question 4. What is the unit of radioactivity? Define it.
Answer: The SI unit of radioactivity is the Becquerel (Bq). One Becquerel is defined as the quantity of a radioactive substance that undergoes one nuclear disintegration (decay) per second. It is a small but precise unit for measuring radioactive activity.
In simple words: The main unit for radioactivity is the Becquerel. If a substance has 1 Becquerel, it means one atom in it breaks down every second.

🎯 Exam Tip: The Becquerel is the modern, international standard unit. Connect its definition directly to the number of decays per unit time.

 

Question 5. Define nuclear fission. State an example.
Answer: Nuclear fission is the process where a heavy atomic nucleus splits into two or more lighter nuclei, releasing a large amount of energy and several neutrons. This process is used in nuclear power plants. An example is the fission of Uranium-235 \( (\text{U}^{235}) \) when hit by a neutron:
\[ _{92}\text{U}^{235} + _{0}\text{n}^{1} \rightarrow _{56}\text{Ba}^{141} + _{36}\text{Kr}^{92} + 3_{0}\text{n}^{1} + \text{Q (energy)} \]
In simple words: Nuclear fission is like splitting a big atom into smaller pieces, which releases a lot of energy and throws out tiny particles called neutrons. For example, when Uranium-235 is hit by a neutron, it splits into Barium and Krypton.

🎯 Exam Tip: For nuclear fission, always remember that it involves splitting a heavy nucleus, releasing energy and neutrons, and is the principle behind nuclear reactors and atomic bombs.

 

Question 6. How a product nucleus is identified in a nuclear reaction?
Answer: In any nuclear reaction, the element formed as the product nucleus is identified by its atomic number, not its mass number. The atomic number, which represents the number of protons, uniquely determines the element.
In simple words: We know what new element is formed in a nuclear reaction by looking at its atomic number, which tells us how many protons it has.

🎯 Exam Tip: The atomic number (Z) is the defining characteristic of an element, as it determines the chemical properties. The mass number (A) can vary, leading to isotopes of the same element.

 

Question 7. What is fissile material?
Answer: Fissile material is a radioactive element capable of undergoing a self-sustaining nuclear fission chain reaction upon absorbing a neutron. These materials are also referred to as 'fissionable materials'. Examples include Uranium-235 \( (\text{U}^{235}) \), Plutonium-239 \( (\text{Pu}^{239}) \), and Plutonium-241 \( (\text{Pu}^{241}) \).
In simple words: A fissile material is a special type of radioactive element that can easily be split by a neutron, causing it to start a chain reaction that keeps going. Uranium-235 is a good example.

🎯 Exam Tip: Understand that for a material to be truly fissile, it must not only fission but also produce enough neutrons to sustain a chain reaction.

 

Question 8. What are fertile materials? Mention examples.
Answer: Fertile materials are radioactive elements that are not fissile themselves but can be converted into fissile materials by absorbing neutrons. Examples include Uranium-238 \( (\text{U}^{238}) \), Thorium-232 \( (\text{Th}^{232}) \), and Plutonium-240 \( (\text{Pu}^{240}) \). Breeder reactors are designed to convert fertile materials into fissile ones.
In simple words: Fertile materials are radioactive elements that cannot easily split on their own but can be changed into split-ready (fissile) materials when they absorb neutrons. Uranium-238 is an example.

🎯 Exam Tip: Distinguish between fissile (can fission easily) and fertile (can become fissile) materials. Both are important in nuclear energy.

 

Question 9. What is the composition of natural uranium?
Answer: Natural uranium primarily consists of \( 99.28\% \) Uranium-238 \( (_{92}\text{U}^{238}) \) and a smaller amount of \( 0.72\% \) Uranium-235 \( (_{92}\text{U}^{235}) \). Uranium-235 is the fissile isotope.
In simple words: Most of the uranium found in nature is Uranium-238, with only a small part being Uranium-235, which is the type used for nuclear reactions.

🎯 Exam Tip: Note the low percentage of fissile U-235 in natural uranium, which is why enrichment is often necessary for nuclear fuel.

 

Question 10. What is nuclear fusion? State an example.
Answer: Nuclear fusion is a process where two or more light atomic nuclei combine to form a heavier nucleus, releasing an enormous amount of energy. This is the process that powers the sun. An example is the fusion of two deuterium nuclei:
\[ _{1}\text{H}^{2} + _{1}\text{H}^{2} \rightarrow _{2}\text{He}^{4} + \text{Q (Energy)} \]
In simple words: Nuclear fusion is when small atoms join together to make a bigger atom, releasing a lot of energy. An example is when two hydrogen atoms combine to form a helium atom.

🎯 Exam Tip: Remember that fusion involves combining light nuclei, requires extremely high temperatures (thermonuclear), and releases more energy per nucleon than fission.

 

Question 11. What is meant by chain reaction?
Answer: A chain reaction is a self-sustaining process in nuclear physics where neutrons released during a fission event cause further fission reactions, leading to a rapid and exponential increase in the number of fissions. This multiplication happens in a geometrical progression.
In simple words: A chain reaction is like a domino effect in nuclear energy: one atom splitting releases particles that make more atoms split, and it keeps going faster and faster.

🎯 Exam Tip: Understand the concept of "self-propagating" and the rapid multiplication of neutrons as key aspects of a chain reaction.

 

Question 12. What is meant by mass defect?
Answer: Mass defect is the difference between the actual mass of an atomic nucleus and the sum of the masses of its individual protons and neutrons. This "missing" mass is converted into binding energy, according to Einstein's equation \( E=mc^2 \).
In simple words: Mass defect is when a nucleus weighs a tiny bit less than the total weight of all its separate parts. This small amount of missing mass is actually turned into the energy that holds the nucleus together.

🎯 Exam Tip: The mass defect is a direct consequence of the strong nuclear force binding nucleons together, and it accounts for the enormous energy released in nuclear reactions.

 

Question 13. Nuclear fusion is named as thermonuclear reaction. Why?
Answer: Nuclear fusion is called a thermonuclear reaction because it requires extremely high temperatures, typically in the range of \( 10^7 \) to \( 10^9 \) K, and very high pressure. These conditions are necessary to overcome the electrostatic repulsion between the positively charged nuclei, allowing them to fuse. Such extreme temperatures are naturally found in the cores of stars.
In simple words: Fusion is called 'thermonuclear' because it needs incredibly high heat, like the heat inside the sun, to make atoms join together.

🎯 Exam Tip: Always emphasize the temperature requirement for fusion, as "thermo" directly relates to heat, and it's the defining characteristic for this type of reaction.

 

Question 14. What are the uses of radio isotopes in industries?
Answer: Radioisotopes have several important applications in industries:
1. Californium-252 \( (\text{Cf}^{252}) \) is used in airport security systems to detect explosives in luggage.
2. Americium-241 \( (\text{Am}^{241}) \) is widely used in smoke detectors.
3. Radioisotopes can also be used as tracers to find leaks in pipes, monitor engine wear, and check for manufacturing defects like cracks in metal.
In simple words: Industries use radioisotopes in various ways, such as finding explosives in bags at airports, powering smoke detectors, and detecting hidden flaws in materials or equipment.

🎯 Exam Tip: When listing industrial uses, remember specific examples like smoke detectors and explosive detection, and generally think of non-destructive testing and process control.

 

Question 15. What is the age of Earth?
Answer: The age of the Earth is estimated to be approximately \( 4.54 \times 10^9 \) years, which is about 4.54 billion years (or 45 crore 40 lakh years). This age is determined using radiometric dating.
In simple words: The Earth is about 4 and a half billion years old.

🎯 Exam Tip: Radiometric dating, which measures the decay of long-lived radioisotopes, is the primary method used to determine the age of the Earth and other geological samples.

 

Question 16. What do you know about dosimeter?
Answer: A dosimeter is a personal device used to measure and track an individual's exposure to ionizing radiation over a period. It helps monitor radiation levels to ensure safety for people working in environments with radiation.
In simple words: A dosimeter is a tool worn by people to check how much radiation they have been exposed to, helping to keep them safe.

🎯 Exam Tip: Dosimeters are crucial for radiation safety professionals, medical personnel, and anyone working near radioactive sources to prevent overexposure.

 

Question 17. What is the function of moderator in a nuclear reactor?
Answer: The primary function of a moderator in a nuclear reactor is to slow down the high-energy neutrons produced during fission. By slowing them down to 'thermal' speeds, these neutrons become much more effective at causing further fission reactions in the fuel, sustaining the chain reaction. Common moderators include graphite and heavy water.
In simple words: A moderator helps slow down the fast particles (neutrons) inside a nuclear reactor, making it easier for them to split atoms and keep the energy process going.

🎯 Exam Tip: Understand that fast neutrons are less likely to cause fission in U-235, so moderation is essential for efficient chain reactions in most reactors.

 

Question 18. How do coolants function in a nuclear reactor?
Answer: Coolants in a nuclear reactor are used to remove the immense heat generated by the nuclear fission reactions in the reactor core. This superheated coolant is then used to produce steam, which drives turbines to generate electricity. Common coolants include water, air, and helium.
In simple words: Coolants take away the heat from inside the nuclear reactor. This hot coolant then makes steam, which is used to create electricity.

🎯 Exam Tip: The coolant system is vital for both electricity generation and for preventing the reactor core from overheating and melting down.

 

Question 19. Name some operating reactors in India.
Answer: Some notable operating nuclear reactors in India include Cirus, Dhruva, and Purnima.
In simple words: India has several nuclear reactors like Cirus, Dhruva, and Purnima that help produce power and conduct research.

🎯 Exam Tip: Knowing specific examples of India's nuclear reactors helps to demonstrate an understanding of the country's nuclear program.

 

Question 20. Define Curie.
Answer: The Curie (Ci) is a non-SI unit of radioactivity. It is defined as the quantity of a radioactive substance that undergoes \( 3.7 \times 10^{10} \) nuclear disintegrations (decays) per second. This value is approximately equal to the activity of 1 gram of radium-226.
In simple words: A Curie is a way to measure how radioactive something is; it represents a very high number of atoms decaying every second, similar to the activity of one gram of radium.

🎯 Exam Tip: While Curie is a historical unit, it's still widely recognized. Always remember its conversion factor to Becquerel (1 Ci = 37 GBq).

IX. Answer the following question in detail.

 

Question 1. Write short notes on induced radioactivity.
Answer: Induced (or artificial/man-made) radioactivity is the process where stable, typically lighter, elements are made radioactive by bombarding them with high-energy particles. This phenomenon was discovered by Irene Curie and F. Joliot in 1934. When a stable nucleus absorbs a projectile particle (like an alpha particle), it becomes unstable and then decays by emitting other particles, transforming into a new, radioactive daughter nucleus. This process allows for the creation of many useful radioisotopes in laboratories.
For example, bombarding Beryllium-9 with an alpha particle \( (\text{He}^{4}) \) can lead to the formation of an unstable Carbon-13 isotope, which then decays by emitting a neutron:
\[ _{4}\text{Be}^{9} + _{2}\text{He}^{4} \rightarrow _{6}\text{C}^{13*} \]
\[ _{6}\text{C}^{13*} \rightarrow _{6}\text{C}^{12} + _{0}\text{n}^{1} \]
In simple words: Induced radioactivity is when we make a stable atom radioactive by shooting tiny particles at it. This makes the atom unstable, so it then releases its own radiation, just like naturally radioactive atoms.

🎯 Exam Tip: Highlight that induced radioactivity involves human intervention (bombardment) to create unstable nuclei, contrasting it with natural radioactivity.

 

Question 2. Explain the concept of 'Hydrogen bomb'.
Answer: A hydrogen bomb, also known as a fusion bomb, operates on the principle of uncontrolled nuclear fusion, which releases an enormous amount of energy. Unlike an atomic bomb, which uses fission, a hydrogen bomb combines lighter atomic nuclei to form heavier ones. To initiate this fusion process, an initial atomic fission bomb is used as a trigger. This fission bomb creates the extremely high temperatures and pressures (thermonuclear conditions) necessary for the fusion of hydrogen isotopes (like deuterium and tritium) to occur. The energy released by a hydrogen bomb is significantly greater than that produced by an atomic fission bomb.
In simple words: A hydrogen bomb uses very small atoms to create a huge explosion by forcing them to join together (fusion). To start this, it first uses a smaller atomic bomb to create the extreme heat needed for the fusion to happen.

🎯 Exam Tip: Remember the two-stage nature of a hydrogen bomb: a fission trigger to create the conditions for fusion, and that fusion releases much more energy than fission.

 

Question 3. Explain (i) alpha decay, (ii) Beta decay, (iii) gamma decay
Answer:
(i) **Alpha decay:** This is a nuclear reaction where an unstable parent nucleus emits an alpha particle, which is a helium nucleus \( (_{2}\text{He}^{4}) \), and transforms into a new daughter nucleus. In alpha decay, the mass number of the nucleus decreases by four, and the atomic number decreases by two. Alpha particles are heavy and positively charged, giving them high ionizing power but low penetrating power. For example, Uranium-238 decaying to Thorium-234: \( _{92}\text{U}^{238} \rightarrow _{90}\text{Th}^{234} + _{2}\text{He}^{4} \).
(ii) **Beta decay:** This is a nuclear reaction where an unstable parent nucleus emits a beta particle, which is an electron \( (_{-1}\text{e}^{0}) \), transforming into a new daughter nucleus. In beta decay, the mass number of the nucleus remains unchanged, but the atomic number increases by one. Beta particles are lighter and faster than alpha particles, with moderate ionizing and penetrating power. For example, Phosphorus-32 decaying to Sulfur-32: \( _{15}\text{P}^{32} \rightarrow _{16}\text{S}^{32} + _{-1}\text{e}^{0} \).
(iii) **Gamma decay:** In gamma decay, an excited nucleus simply releases excess energy in the form of a gamma ray (a high-energy photon). During this process, neither the atomic number nor the mass number of the nucleus changes; only its energy state decreases. Gamma rays have no mass or charge, giving them very high penetrating power but low ionizing power. Gamma decay often follows alpha or beta decay when the daughter nucleus is left in an excited state.
In simple words: Alpha decay means an atom shoots out a heavy, positive particle, changing into a lighter atom. Beta decay means an atom shoots out an electron, changing into a slightly different type of atom. Gamma decay means an atom simply releases extra energy as a strong light wave, without changing its type or weight.

🎯 Exam Tip: Clearly remember how each decay type affects the atomic number (Z) and mass number (A), as well as the charge and mass characteristics of the emitted particle.

Question 4. Explain the process of controlled and uncontrolled chain reactions.
Answer:
(i) Controlled chain reaction: In this type of reaction, the number of neutrons causing fission is kept steady at one. Any extra neutrons are absorbed by special materials, which allows the reaction to continue in a stable way. The energy produced from a controlled chain reaction is used for good purposes, like generating electricity in nuclear power plants.
(ii) Uncontrolled chain reaction: Here, the number of neutrons multiplies very quickly and without limits, causing a large amount of fissile material to split. This releases an enormous amount of energy in a very short time. This kind of chain reaction is what powers an atom bomb, leading to an explosion.
In simple words: A controlled chain reaction is like a steady fire for power, while an uncontrolled one is like an explosion. Keeping neutrons balanced is key for safe energy.

🎯 Exam Tip: Remember that "controlled" means stable energy production (nuclear reactor), while "uncontrolled" means rapid energy release (atom bomb).

 

Question 5. What precautions are to be took for those, who are working in radiation laboratories?
Answer:
1. Radioactive materials should be kept safe in containers with thick lead walls. This helps block harmful radiation.
2. People working with dangerous radioactive materials should wear aprons and gloves that are coated with lead.
3. Workers must not eat or drink while handling radioactive substances. This prevents accidental exposure.
4. Radioactive materials should only be handled with long tongs or by using special remote-control tools, never directly.
5. Workers should wear dosimeters, which are small devices that measure how much radiation they have been exposed to.
In simple words: To stay safe, workers in radiation labs must use lead shielding, special tools, and protective gear, and should never eat or drink near radioactive items.

🎯 Exam Tip: Always prioritize personal protective equipment (PPE) and proper handling techniques when dealing with radioactive substances to minimize exposure.

 

Question 6. What do you know about hydrogen bomb?
Answer: A hydrogen bomb works using the principle of nuclear fusion. It contains a smaller atomic bomb inside, which explodes first. This initial explosion creates extremely high temperatures and pressure. These conditions then trigger the main hydrogen fuel to undergo fusion, releasing an enormous amount of energy in an uncontrolled way. The energy released by a hydrogen bomb is far greater than that from an atomic bomb.
In simple words: A hydrogen bomb uses a small atom bomb to start a huge fusion reaction, releasing a lot more energy than a regular atom bomb.

🎯 Exam Tip: Understand that hydrogen bombs rely on fusion, which needs extreme heat to start, often provided by a fission reaction.

 

Question 7. What are the applications of radio isotopes in medicine?
Answer: Radioisotopes have two main uses in medicine: helping to find out what's wrong (diagnosis) and helping to treat illnesses (therapy).
Specific uses include:
1. Radio-sodium (\( \text{Na}^{24} \)) helps check how well the heart is working.
2. Radio-iodine (\( \text{I}^{131} \)) is used to treat goiter, a thyroid condition.
3. Radio-iron (\( \text{Fe}^{59} \)) helps diagnose and treat anaemia, a blood disorder.
4. Radio-phosphorus (\( \text{P}^{32} \)) is used to treat various skin diseases.
5. Radio-cobalt (\( \text{Co}^{60} \)) and radio-gold (\( \text{Au}^{198} \)) are both used in the treatment of skin cancer.
6. Radiation is also used to make surgical tools sterile by killing harmful germs.
In simple words: Radioisotopes help doctors find diseases and treat them, like checking hearts, curing thyroid issues, treating blood disorders, and sterilizing medical tools.

🎯 Exam Tip: For medical applications, focus on specific radioisotopes and their corresponding diagnostic or therapeutic uses, such as \( \text{I}^{131} \) for goiter.

 

Question 8. Mention the applications of radio isotopes in agriculture and industries and archeological research.
Answer:
Agriculture: Radioisotopes like phosphorus-32 (\( \text{P}^{32} \)) help plants grow better and increase crop yields. Radiation from radioisotopes can also kill insects and pests, preventing agricultural products from spoiling. This helps keep foods such as cereals, onions, potatoes, and gram fresh for longer by stopping them from sprouting.
Industries: In factories, radioactive isotopes are used as tracers to find hidden flaws like cracks or leaks in manufactured goods. They also help check the fill levels of liquids, gases, and solids in containers. For example, californium-252 (\( \text{Cf}^{252} \)) is used at airports to detect explosives in luggage, and americium-241 (\( \text{Am}^{241} \)) is used in smoke detectors.
Archeological research: Scientists use a method called radiocarbon dating to determine the age of ancient items and sites. By measuring the remaining amount of radiocarbon in things like the Earth's fossils, old paintings, and historical monuments, they can estimate how old these objects are.
In simple words: Radioisotopes help crops grow, find problems in factories, detect explosives, and tell us the age of old items like fossils.

🎯 Exam Tip: When discussing applications, always link the specific radioisotope to its function (e.g., \( \text{P}^{32} \) in agriculture, \( \text{Am}^{241} \) in smoke detectors, carbon-14 in dating).

 

Question 9. Compare the features of nuclear fission with nuclear fusion.
Answer: