Text Book Back Questions and Answers - Chapter 6 Nuclear Physics 10th Science Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

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Chapter 6 - Nuclear Physics - 10th Science Guide Samacheer Kalvi Solutions

Question $1 .$
Identify A, B, C, and D from the following nuclear reactions.

Solution:

$\mathrm{A}$ is alpha particle, $\mathrm{B}$ is neutron, $\mathrm{C}$ is proton and $\mathrm{D}$ is electron.

Question $2 .$
A radon specimen emits radiation of $3.7 \times 10^{3} \mathrm{GBq}$ per second. Convert this disintegration in terms of a curie, (one curie $=3.7 \times 10^{10}$ disintegration per second)
Solution:
$1 \mathrm{~Bq}=$ one disintegration per second
one curie $=3.7 \times 10^{10} \mathrm{~Bq}$
$$
\begin{aligned}
1 \mathrm{~Bq} &=\frac{1}{3.7 \times 10^{10}} \text { curie } \\
\therefore 3.7 \times 10^{3} \mathrm{G} \mathrm{Bq} &=3.7 \times 10^{3} \times 10^{9} \times \frac{1}{3.7 \times 10^{10}} \\
&=100 \text { curie }
\end{aligned}
$$

Question $3 .$
${ }_{92} \mathrm{U}^{235}$ experiences one $\alpha$ - decay and one $\beta$ - decay. Find the number of neutrons in the final daughter nucleus that is formed.
Solution:
Let $\mathrm{X}$ and $\mathrm{Y}$ be the resulting nucleus after the emission of the alpha and beta particles respectively.
${ }_{92} \mathrm{U}^{235} \stackrel{\alpha \text { decay }}{\longrightarrow}{ }_{90} \mathrm{X}^{231}+{ }_{2} \mathrm{He}^{4}$
${ }_{90} \mathrm{X}^{231} \stackrel{\beta \text { decay }}{\longrightarrow}{ }_{91} \mathrm{Y}^{231}+{ }_{-1} \mathrm{e}^{0}$
Number of neutrons $=$ Mass number $-$ Atomic number $=231-91=140$.

Question $4 .$
Calculate, the amount of energy released when a radioactive substance undergoes fusion and results in a mass defect of $2 \mathrm{~kg}$.
Solution:
Mass defect in the reaction $(\mathrm{m})=2 \mathrm{~kg}$
Velocity of light $(\mathrm{c})=3 \times 10^{8} \mathrm{~ms}^{-1}$
By Einstein's equation,
Energy released $\mathrm{E}=\mathrm{mc}^{2}$
$$
\begin{aligned}
&=2 \times\left(3 \times 10^{8}\right)^{2} \\
&=1.8 \times 10^{17} \mathrm{~J}
\end{aligned}
$$

I. Choose the correct answer
Question $1 .$
Man - made radioactivity is also known as
(a) Induced radioactivity
(b) Spontaneous radioactivity
(c) Artificial radioactivity
(d) (a) \& (c).
Answer:
(d) (a) \& (c).

Question $2 .$
Unit of radioactivity is:
(a) roentgen
(b) curie
(c) becquerel
(d) all the above
Answer:
(d) all the above

Nuclear Physics Question $3 .$
Artificial radioactivity was discovered by
(a) Becquerel
(b) Irene Curie
(c) Roentgen
(d) Neils Bohr.
Answer:
(b) Irene Curie

Question $4 .$
In which of the following, no change in mass number of the daughter nuclei takes place:
(i) a decay;
(ii) $P$ decay
(iii) y decay
(iv) neutron decay
(a) (i) is correct
(b) (ii) and (iii) are correct
(c) (i) and (iv) are correct

(d) (ii) and (iv) are correct
Answer:
(b) (ii) and (iii) are correct

Question 5 .
isotope is used for the treatment of cancer.
(a) Radio Iodine
(b) Radio Cobalt
(c) Radio Carbon
(d) Radio Nickel.
Answer:
(b) Radio Cobalt

Question $6 .$
Gamma radiations are dangerous because:
(a) it affects eyes and bones
(b) it affects tissues
(c) it produces genetic disorder
(d) it produces an enormous amount of heat
Answer:
(c) it produces genetic disorder

Question $7 .$
__________aprons are used to protect us from gamma radiations.
(a) Lead oxide
(b) Iron
(c) Lead
(d) Aluminium.
Answer:
(c) Lead
 

Question $8 .$
Which of the following statements is / are correct?
(i) $\alpha$ particles are photons
(ii) Penetrating power of $\gamma$ radiation is very low
(iii) Ionization power is maximum for $\alpha$ rays
(iv) Penetrating power of $\gamma$ radiation is very high
(a) (i) \& (ii) are correct
(b) (ii) \& (iii) are correct
(c) (iv) only correct
(d) (iii) \& (iv) are correct.
Answer:
(d) (iii) \& (iv) are correct.

Question $9 .$
Proton-Proton chain reaction is an example of:
(a) Nuclear fission
(b) $\alpha-$ decay
(c) Nuclear fusion
(d) $\beta-$ decay
Answer:
(c) Nuclear fusion
 

Question $10 .$
In the nuclear reaction ${ }_{6}^{\mathrm{X}^{12}} \stackrel{\alpha \text { decay }}{\longrightarrow} \mathrm{z}^{\mathrm{Y}}$, the value of $\mathrm{A} \& \mathrm{Z}$.
(a) 8,6
(b) 8,4
(c) 4,8
(d) cannot be determined with the given data.
Answer:
(c) 4,8
 

Question $11 .$
Kamini reactor is located at
(a) Kalpakkam
(b) Koodankulam
(c) Mumbai
(d) Rajasthan.
Answer:
(a) Kalpakkam

Question $12 .$
Which of the following is/are correct?
(i) Chain reaction takes place in a nuclear reactor and an atomic bomb.
(ii) The chain reaction in a nuclear reactor is controlled.
(iii) The chain reaction in a nuclear reactor is not controlled.
(iv) No chain reaction takes place in an atom bomb.
(a) (i) only correct
(b) (i) \& (ii) are correct
(c) (iv) only correct
(d) (iii) \& (iv) are correct
Answer:
(b) (i) \& (ii) are correct

II. Fill in the blanks

Question $1 .$
One roentgen is equal to ______ disintegrations per second?
Answer:
$3.7 \times 10^{10}$
 

Question 2.
Positron is an ______
Answer:
antiparticle of electron.
 

Question $3 .$
Anaemia can be cured by ______ isotope.
Answer:
Radio iron $\left(\mathrm{Fe}^{59}\right)$.
 

Question $4 .$
Abbreviation of ICRP ______
Answer:
International Commission on Radiological Protection.
 

Question $5 .$
______is used to measure the exposure rate of radiation in humans.
Answer:
Roentgen.
 

Question $6 .$
______has the greatest penetration power.
Answer:
Gamma ray.

Question $7 .$
$z^{Y^{A}} \rightarrow \mathrm{Z}+1 \mathrm{Y}^{\mathrm{A}}+\mathrm{X} ;$ Then $\mathrm{X}$ is_______
Answer:
$-1 \mathbf{e}^{0}(\beta$ decay)
 

Question $8 .$
$z^{\mathrm{X}^{A}} \rightarrow \mathrm{Y}_{\mathrm{Y}}^{\mathrm{A}}$ This reaction is possible in_______ decay.
Answer:
Gamma ( $\gamma)$
 

Question $9 .$
The average energy released in each fusion reaction is about_______ $J$

Answer:
$3.84 \times 10^{-12}$
 

Question $10 .$
Nuclear fusion is possible only at an extremely high temperature of the order of_______ $\mathrm{K} .$
Answer:
$10^{7}$ to $10^{9}$.
 

Question $11 .$
The radioisotope of_______ helps to increase the productivity of crops.
Answer:
phosphorous $(\mathrm{P}-32)$
 

Question $12 .$
If radiation exposure is $100 \mathrm{R}$, it may cause_______
Answer:
fatal disease.
 

III. State whether the following statements are true or false: If false, correct the statement
Question $1 .$
Plutonium $-239$ is a fissionable material.
Answer:
True.

Question $2 .$
Elements having an atomic number greater than 83 can undergo nuclear fusion.
Answer:
False.
Correct Statement: Elements having an atomic number greater than 83 can undergo nuclear fusion.
 

Question $3 .$
Nuclear fusion is more dangerous than nuclear fission.
Answer:
False.
Correct Statement: Nuclear fission is more dangerous than nuclear fusion. Because the average
energy released in fission $\left(3.2 \times 10^{-11} \mathrm{~J}\right)$ process is more than the average energy released in fusion $\left(3.84 \times 10^{-12} \mathrm{~J}\right)$
 

Question $4 .$
Natural uranium U-238 is the core fuel used in a nuclear reactor.
Answer:
False.
Correct Statement: U-238 is not a fissile material but are abundant in nature. But in a reactor, this can be converted into a fissile material $\mathrm{Pu}^{239}$ and $\mathrm{U}^{233}$. Only fissile materials are used in the fuel of a nuclear reactor.
 

Question $5 .$
If a moderator is not present, then a nuclear reactor will behave like an atom bomb.
Answer:
True.

Question $6 .$
During one nuclear fission on an average, 2 to 3 neutrons are produced.
Answer:
True.
 

Question 7.
Einstein's theory of mass-energy equivalence is used in nuclear fission and fusion.
Answer:
True.
 

IV. Match the following
Question 1.

Answer:
1. (c) Mumbai
2. (d) Tarapur
3. (a) Kalpakkam
4. (b) Apsara
 

Question $2 .$

Answer:
1. (d) uranium
2. (c) Graphite
3. (b) heavy water
4. (a) lead
 

Question $3 .$

Answer:
1. (b) Displacement law
2. (d) Artificial Radioactivity
3. (a) Natural radioactivity
4. (c) Mass energy equivalence
 

Question 4 .

Answer:
1. (d) Atom bomb
2. (c) Breeder reactor
3. (b) Nuclear Reactor
4. (a) Hydrogen Bomb
 

Question $5 .$

Answer:
1. (c) Leukemia
2. (d) Thyroid disease
3. (b) Function of Heart
4. (a) Age of fossil
 

V. Arrange the following in the correct sequence
Question $1 .$
Arrange in descending order, on the basis of their penetration power.
1. Alpha rays
2. Beta rays
3. Gamma rays
4. Cosmic rays.
Answer:
1. Gamma rays
2. Beta rays
3. Alpha rays
4. Cosmic rays.
 

Question $2 .$
Arrange the following in the chronological order of discovery.
1. A nuclear reactor
2. Radioactivity
3. Artificial radioactivity
4. Discovery of radium.
Answer:
1. Radioactivity (1896)
2. Discovery of radium (1898)
3. Artificial radioactivity (1934)
4. Nuclear reactor (1942).
 

VI. Use the analogy to fill in the blank

Question $1 .$
Spontaneous process : Natural Radioactivity, Induced process:
Answer:
Artificial radioactivity
(or)
Man - made activity.
 

Question 2.
Nuclear Fusion : Extreme temperature, Nuclear Fission:
Answer:
Room temperature.
 

Question $3 .$
Increasing crops : Radio phosphorous, Effective functioning of heart:
Answer:
Radio sodium $\left(\mathrm{Na}^{24}\right)$.
 

Question $4 .$
Deflected by electric field : $\alpha$ ray, Null Deflection:
Answer:
$\gamma$ ray (Gamma - ray).
 

VII. Numerical Problems
Question $1 .$
$88^{\mathrm{Ra}^{226}}$ experiences three $\alpha$-decay. Find the number of neutrons in the daughter element.

Solution:
$88^{\mathrm{Ra}^{226}}$ consider as a parent element that is $88^{\mathrm{X}^{226}}$ and their daughter element is $z^{\mathrm{Y}^{A}}$
According to $\alpha$ decay process,
$88^{\mathrm{X} 26} \stackrel{3 \alpha \text { decay }}{\longrightarrow} 82^{214}+3 \alpha$ decay
During the $3 \alpha$ decay, the atomic number decreases by 6 and mass number decreases by 12 .
So the number of neutrons in the daughter element
$\mathrm{N}=\mathrm{A}-\mathrm{Z}$
$N=214-88=126$
Number of neutrons in the daughter element $N=126$.
 

Question $2 .$
A cobalt specimen emits induced radiation of $75.6$ millicurie per second. Convert this disintegration in to becquerel (one curie $=3.7 \times 10^{10} \mathrm{~Bq}$ ).
Solution:
Cobalt specimen emits induced radiation $=75.6$ millicurie per second
$\left(1\right.$ curie $=3.7 \times 10^{10} \mathrm{~Bq}$ )

So $75.6$ millicurie $=75.6 \times 10^{3} \times 1$ curie
$$
\begin{aligned}
&=75.6 \times 10^{-3} \times 3.7 \times 10^{10} \mathrm{~Bq} \\
&=279.72 \times 10^{7} \\
&=2.7972 \times 10^{9} \mathrm{~Bq}
\end{aligned}
$$
$75.6$ millicurie per second is equivalent to $2.7972 \times 10^{9} \mathrm{~Bq}$.
 

VIII. Assertion and Reason Type Questions
Mark the correct choice as
(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) Assertion is true, but the reason is false.
(d) Assertion is false, but the reason is true.
 

Question $1 .$
Assertion: A neutron impinging on $\mathrm{U}^{235}$, splits it to produce Barium and Krypton.
Reason: U-235 is a fissile material.
Answer:
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.

Question $2 .$
Assertion: In a $\beta$ - decay, the neutron number decreases by one.
Reason: In $\beta$ - decay atomic number increases by one.
Answer:
(d) The assertion is false, but the reason is true.
Explanation: In $\beta$-decay there is no change in the mass number of the daughter nucleus but the atomic number increases by one.
 

Question $3 .$
Assertion: Extreme temperature is necessary to execute nuclear fusion.
Reason: In nuclear fusion, the nuclei of the reactants combine releasing high energy.
Answer:
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
 

Question $4 .$
Assertion: Control rods are known as 'Neutron seeking rods'
Reason: Control rods are used to perform a sustained nuclear fission reaction.
Answer:

(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
Explanation: Control rods are used to control the number of neutrons in order to have a sustained the chain reaction. They absorb the neutrons, (they seeking the neutrons)
 

IX. Answer in one or two words (VSA)
Question $1 .$
Who discovered natural radioactivity?
Answer:
Henri Becquerel was discovered natural radioactivity.
 

Question $2 .$
Which radioactive material is present in the ore of pitchblende?
Answer:
Uranium
 

Question $3 .$
Write any two elements which are used for inducing radioactivity?
Answer:
1. Boron and Aluminium.
2. Alpha particle and neutron.
 

Question $4 .$
Write the name of the electromagnetic radiation which is emitted during a natural radioactivity.
Answer:
Gamma rays

Question $5 .$
If $\mathrm{A}$ is a radioactive element which emits an $\alpha$-particle and produces ${ }_{104} R f^{259}$. Write the atomic number and mass number of the element $A$.
Answer:
In $\alpha$ decay
$$
{ }_{z} \mathrm{X}^{\mathrm{A}} \frac{\alpha \text { decay }}{263} \times \mathrm{z}-2 \mathrm{Y}^{\mathrm{A}-4}+{ }_{2} \mathrm{He}^{4}(\alpha \text { decay })
$$
$106^{\mathrm{X}^{263} \alpha} \stackrel{\text { decay }}{\longrightarrow} 104 \mathrm{Rf}^{259}+{ }_{2} \mathrm{He}^{4}$
In element A having atomic number is 106 and mass number is 263 .
 

Question $6 .$
What is the average energy released from a single fission process?
Answer:
The average energy released from a single fission process is about $3.2 \times 10^{-11} \mathrm{~J}$.

Question 7.
Which hazardous radiation is the cause for the genetic disorders (or) effect?
Answer:
Radioactive radiations
 

Question 8 .
What is the amount of radiation that may cause the death of a person when exposed to it?
Answer:
When the body is exposed to about $600 \mathrm{R}$, it leads to death.
 

Question $9 .$
When and where was the first nuclear reactor built?
Answer:
The first nuclear reactor was built in 1942 in Chicago, USA.
 

Question 10 .
Give the SI unit of radioactivity.
Answer:
Becquerel
 

Question $11 .$
Which material protects us from radiation?
Answer:
Lead coated aprons and lead gloves should be used while working with the hazardous area. These materials are used to protects us from radiation.
 

$X$. Answer the following questions in a few sentences.
Question $1 .$
Write any three features of natural and artificial radioactivity.
Answer:

Question $2 .$
Define critical mass.
Answer:
The minimum mass of fissile material necessary to sustain the chain reaction is called 'critical mass $\left(m_{c}\right)$. It depends on the nature, density and the size of the fissile material.
 

Question $3 .$
Define One roentgen.
Answer:
One roentgen is defined as the quantity of radioactive substance which produces a charge of $2.58 \times$ $10^{-4}$ coulomb in $1 \mathrm{~kg}$ of air under standard conditions of pressure, temperature and humidity.
 

Question $4 .$
State Soddy and Fagan's displacement law.
Answer:
During a radioactive disintegration, the nucleus which undergoes disintegration is called a parent nucleus and that which remains after the disintegration is called the daughter nucleus.
 

Question $5 .$
Give the function of control rods in a nuclear reactor.
Answer:
Control rods are used to control the number of neutrons in order to have sustained chain reaction.
Mostly boron or cadmium rods are used as control rods. They absorb the neutrons.

Question $6 .$
In Japan, some of the newborn children are having congenital diseases. Why?
Answer:
During the Second World War American, a bomber dropped the nuclear weapons over the Japanese cities of Hiroshima and Nagasaki. In the explosion of the atomic bomb to release the high energy dangerous radiation. In the explosion period, Japanese peoples are affected by radiation. This is the reason in Japan, some of the newborn children are having congenital diseases.

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:
$\mathrm{X}$ - rays have a destructive effect on living tissue. When the human body is exposed to $\mathrm{X}$ - rays, it causes redness of the skin, sores and serious injuries to the tissues and glands. They destroy the white corpuscles of the blood. If you don't wear the lead aprons these kinds of diseases formed in your body. In my suggestion, you must wear lead aprons.

Question 8 .
What is stellar energy?
Answer:
Fusion reaction that takes place in the cores of the Sun and other stars results in an enormous amount of energy, which is called as stellar energy.

Question $9 .$
Give any two uses of radioisotopes in the field of agriculture?
Answer:
- The radioisotope of phosphorus $(\mathrm{P}-32)$ helps to increase the productivity of crops.
- The radiations from the radioisotopes can be used to kill the insects and parasites and prevent the wastage of agricultural products.
 

XI. Answer the following questions in detail.
Question $1 .$
Explain the process of controlled and uncontrolled chain reactions.
Answer:
(a) Controlled chain reaction
- In the controlled chain reaction, the number of neutrons released is maintained to be one. This is achieved by absorbing the extra neutrons with a neutron absorber leaving only one neutron to produce further fission.
- Thus, the reaction is sustained in a controlled manner. The energy released due to a controlled chain reaction can be utilized for constructive purposes.
- The controlled chain reaction is used in a nuclear reactor to produce energy in a sustained and controlled manner.
(b) Uncontrolled chain reaction:
- In the uncontrolled chain reaction, the number of neutrons multiplies indefinitely and causes fission in a large amount of the fissile material.
- This results in the release of a huge amount of energy within a fraction of a second.

- This kind of chain reaction is used in the atom bomb to produce an explosion.

Question $2 .$
Compare the properties of Alpha, Beta and Gamma radiations.

Answer:

Question $3 .$
What is a nuclear reactor? Explain its essential parts with their functions.
Answer:
Nuclear reactor: A Nuclear reactor is a device in which the nuclear fission reaction takes place in a self - sustained and controlled manner to produce electricity.

Components of a Nuclear Reactor:
The essential components of a nuclear reactor are
- Fuel: A fissile material is used as the fuel. The commonly used fuel material is uranium.
- Moderator: A moderator is used to slow down the high energy neutrons to provide slow neutrons. Graphite and heavy water are commonly used moderators.
- Control rod: Control rods are used to control the number of neutrons in order to have a sustained a chain reaction. Mostly boron or cadmium rods are used as control rods. They absorb the neutrons.
- Coolant: A coolant is used to remove the heat produced in the reactor core, to produce steam. This steam is used to run a turbine in order to produce electricity. Water, air and helium are some of the coolants.
- Protection wall: A thick concrete lead wall is built around the nuclear reactor in order to prevent the harmful radiations from escaping into the environment.

XII. HOT Questions
Question $1 .$
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 isotope of lead with a mass number 208 and an atomic number 82 . Determine the number of alpha and beta decay that can occur.
Answer:
Mass number $A=232$
Atomic number $Z=90$
Daughter element:
Mass number $A=208$
Atomic number $Z=82$
Difference in mass number $=232-208=24$
Difference in atomic number
$$
=90-82=8
$$
Atomic number of $\alpha=2$
Atomic number of $\beta=-1$
Mass number of $\alpha=4$
Mass number of $\beta=0$
Difference in mass number in transformations
$$
=24
$$
Number of a decays $=\frac{24}{4}=6$
Difference in atomic number $=8$
$$
\begin{aligned}
&\Delta Z=6 \alpha+4 \beta \\
&=6(2)+4(-1) \\
&=12-4 \\
&=8
\end{aligned}
$$
$\therefore$ Number of $\beta$ decays $=4$
$\therefore$ Number of $\alpha$ decays $=6$
$\therefore$ Number of $\beta$ decays $=4$
 

Question $2 .$
' $\mathrm{X}$ - rays should not be taken often'. Give the reason.
Answer:
- Radiation does involve in $\mathrm{X}$ - rays tests and isotope scans (in nuclear medicine) are too low to cause immediate hazardous effects.
- If should be taken often, $\mathrm{X}$ - ray radiation from medical examinations though slightly increases one's risk for cancer which can occur year or decades after X-ray exposure.

Question 3 .
Cell phone towers should be placed far away from the residential area. why?
Answer:
1. Living near a cell phone tower is not healthy. There is multiple health risks associated with living near a cell phone tower.
2. Cell phone towers communicate by use pulsed microwave signals (radiofrequency radiation) with each other.
3. That is the reason cell phone towers should be placed far away from the residential area.
 

I. Choose the best Answer.
Question $1 .$
Radium was discovered by
(a) Marie curie
(b) Irene curie
(c) Henri Becquerel
(d) F. Joliot.
Answer:
(a) Marie Curie
 

Question $2 .$
How many radioactive substances discovered so far?
(a) 83
(b) 92
(c) 43
(d) 29
Answer:
(d) 29

Question 3.
The SI unit of Radioactivity is
(a) Curie
(b) Rutherford
(c) Becquerel
(d) Roentgen (R).
Answer:
(c) Becquerel
 

Question 4.
Radioactivity is
(a) increases with increase in temperature
(b) increases with increase in pressure
(c) depends on the number of electrons
(d) purely a nuclear phenomenon.
Answer:
(d) purely a nuclear phenomenon
 

Question $5 .$
Which of the following processes is a spontaneous process?
(a) Artifical radioactivity
(b) Natural radioactivity
(c) Photoelectric effect
(d) Collisions
Answer:
(b) Natural radioactivity

Question $6 .$
The charge of the $\beta$ rays
(a) $2 \mathrm{e}$
(b) 0
(c) -e
(d) none of these.
Answer:
(c) -e
 

Question 7.
The charge of the $\gamma$ rays
(a) $2 \mathrm{e}$
(b) 0
(c) $-\mathrm{e}$
(d) none of these.
Answer:
(b) 0
 

Question $8 .$
The atomic number of the elements that exhibit artifical radioactivity is:
(a) more than 82
(b) more than 83
(c) less than 83
(d) less than 82
Answer:
(c) less than 83
 

Question $9 .$
Arrange $\alpha, \beta, \gamma$ rays in the increasing order of their ionizing power.
(a) $\alpha, \beta, \gamma$
(b) $\beta, \alpha, \gamma$
(c) $\gamma, \beta, \alpha$

(d) $\gamma, \alpha, \beta$.
Answer:
(c) $\gamma, \beta, \alpha$
 

Question $10 .$
Which produces a charge of $2.58 \times 10^{-4}$ Coulomb in $1 \mathrm{Kg}$ of air?
(a) Curie
(b) Becquerel
(c) Rutherford
(d) Roentgen
Answer:
(d) Roentgen
 

Question $11 .$
Ionising power of the $\gamma$ rays
(a) Comparatively very high ionization power
(b) 100 times greater than the $\alpha$ rays
(c) 100 times greater than the $\beta$ rays
(d) Comparatively very less ionization power.
Answer:
(d) Comparatively very less ionization power.
 

Question $12 .$
Ionization power maximum for
(a) neutrons
(b) $\alpha$ particles
(c) $\gamma$ rays
(d) B particles.
Answer:
(b) $\alpha$ particles
 

Question $13 .$
Charge of gamma particle is:
(a) $+2 \mathrm{e}$
(b) $-\mathrm{e}$
(c) Zero
(d) $+1 e$
Answer:
(c) Zero

Question $14 .$
Which has low penetrating power?
(a) $\alpha$ rays
(b) $\gamma$ rays
(c) $\beta$ rays
(d) X rays.
Answer:
(a) $\alpha$ rays
 

Question $15 .$
In $\beta$-decay
(a) atomic number decreases by one
(b) the mass number decreases by one
(c) proton number remains the same
(d) neutron number decreases by one.
Answer:
(d) neutron number decreases by one
 

Question $16 .$
In which decay the energy level of the nucleus changes:
(a) $\alpha$-decay
(b) $\beta$-decay
(c) $\gamma$-decay
(d) neutron decay
Answer:
(c) $\gamma$-decay

Question $17 .$
In $\gamma$ - decay
(a) atomic number decreases by one
(b) there is no change in atomic and mass number
(c) energy only changes in the decay process
(d) both (b) and (c).
Answer:
(d) both (b) and (c).
 

Question $18 .$
The unit of decay constant is
(a) no unit
(b) second
(c) second ${ }^{-1}$
(d) curie.
Answer:
(c) second ${ }^{-1}$
 

Question $19 .$
The range of temperature required for nuclear fusion is from:
(a) $10^{7}$ to $10^{9} \mathrm{~K}$
(b) $10^{-9}$ to $10^{-7} \mathrm{~K}$
(c) $10^{5}$ to $10^{9}$
(d) $10^{5}$ to $10^{7} \mathrm{~K}$
Answer:
(a) $10^{7}$ to $10^{9} \mathrm{~K}$

Question 20 .
$1 \mathrm{Rd}$ is equal to
(a) $10^{6}$ decay $/$ second
(b) 1 decay / second
(c) $3.7 \times 10^{10}$ becquerel
(d) $1.6 \times 10^{12}$ decay / second.
Answer:
(a) $10^{6}$ decay $/$ second
 

Question $21 .$
An element $Z^{X^{A}}$ successively undergoes three $\alpha$ decays and four $\beta$ decays and gets converted an element $\mathrm{Y}$ are respectively
(a) $Z-6 Y^{A-12}$
(b) $Z+2 Y^{A-12}$
(c) $Z-2 Y^{A-12}$
(d) $Z-10^{A-12}$.
Answer:
(c) $Z-2 Y^{A-12}$
 

Question $22 .$
In the nuclear reaction ${ }_{88} \mathrm{Ra}^{226} \rightarrow \mathrm{X}+{ }_{2} \mathrm{He}^{4} \mathrm{X}$ is:
(a) $90 \mathrm{Th}^{234}$
(b) $91 \mathrm{~Pa}^{234}$
(c) $8{ }_{6} \mathrm{Rn}^{222}$
(d) $88 \mathrm{Rn}^{226}$
Answer:
(d) ${ }_{88} \mathrm{Rn}^{226}$

Question $23 .$
Which one of the following is used in the treatment of skin diseases
(a) $\mathrm{Na}^{24}$
(b) $\mathrm{I}^{31}$
(c) $\mathrm{Fe}^{59}$
(d) $\mathrm{P}^{32}$
Answer:
(d) $\mathrm{P}^{32}$.
 

Question $24 .$
Anaemia can be diagnosed by
(a) ${ }_{15} P^{31}$
(b) $15 P^{32}$
(c) $26 P^{59}$
(d) $11 P^{24}$.
Answer:
(c) $26 P^{59}$
 

Question $25 .$
Which is used as a coolant?
(a) Graphite
(b) Liquid sodium
(c) Boron
(d) Cadmium
Answer:
(b) Liquid sodium
 

Question $26 .$
The energy released per fission is
(a) $220 \mathrm{MeV}$
(b) $300 \mathrm{MeV}$
(c) $250 \mathrm{MeV}$
(d) $200 \mathrm{MeV}$.
Answer:
(d) $200 \mathrm{MeV}$.

Question $27 .$
In the reaction ${ }_{1} \mathrm{~N}^{14}+{ }_{0} \mathrm{n}^{1} \rightarrow \mathrm{X}+{ }_{1} \mathrm{H}^{1} \mathrm{X}$ is:
(a) ${ }_{15} \mathrm{P}^{30}$
(b) ${ }_{6} \mathrm{C}^{14}$
(c) ${ }_{6} \mathrm{C}^{12}$
(d) ${ }_{11} \mathrm{Na}^{23}$
Answer:
(c) ${ }_{6} \mathrm{C}^{12}$
 

Question $28 .$
Natural uranium consists of
(a) $99.72 \%$ of U-238
(b) $0.28 \%$ of U-238
(c) $0.72 \%$ of U-238
(d) $99.28 \%$ of U-238.
Answer:
(d) $99.28 \%$ of $\mathrm{U}-238$.

Question $29 .$
The number of power reactors in India is
(a) 14
(b) 12
(c) 7
(d) 2 .
Answer:
(a) 14
 

Question $30 .$
In the nucleus of ${ }_{11} \mathrm{Na}^{23}$ the number of protons and neutrons are:
(a) 12,11
(b) 10,12
(c) 11,12
(d) 11,23
Answer:
(c) 11,12
 

Question 31 .
The moderator used in nuclear reactor is
(a) cadmium
(b) boron carbide
(c) heavy water
(d) uranium $\left({ }_{92} \mathrm{U}^{235}\right)$.
Answer:
(c) heavy water

Question $32 .$
The first nuclear reactor was built at
(a) Kalpakkam, India
(b) Hiroshima, Japan
(c) Chicago, USA
(d) Trombay, Bombay.
Answer:
(c) Chicago, USA
 

Question $33 .$
Which of the following is used in the treatment of skin cancer?
(a) Radio Cobalt
(b) Radio gold
(c) Radio Cobalt and radio gold
(d) none of the above
Answer:
(c) Radio Cobalt and radio gold
 

Question $34 .$
The explosion of an atom bomb is based on the principle of
(a) uncontrolled fission reaction
(b) fusion reaction
(c) controlled fission reaction
(d) none of the above.
Answer:
(a) uncontrolled fission reaction

Question 35 .
The reactor in which no moderator used is
(a) fast breeder reactor
(b) pressurised water reactor
(c) pressurised heavy water reactor
(d) boiled water reactor.
Answer:
(a) fast breeder reactor
 

Question $36 .$
The number of neutrons present in ${ }_{92} \mathrm{U}^{235}$ is:
(a) 133
(b) 143
(c) 43
(d) 243
Answer:
(b) 143

Question 37 .
In fast breeder, the coolant system used is
(a) heavy water
(b) light water
(c) liquid sodium
(d) boiled water.
Answer:
(c) liquid sodium
 

Question $38 .$
The only reactor in the world which uses U-233 as fuel is
(a) Zerlina
(b) Purnima
(c) Kamini
(d) Tires.
Answer:
(c) Kamini
 

Question $39 .$
The temperature of the interior of Sun is about
(a) $1.4 \times 10^{7} \mathrm{~K}$
(b) $10^{8} \mathrm{~K}$
(C) $14 \times 10^{7} \mathrm{~K}$
(d) $600 \mathrm{~K}$.
Answer:
(a) $1.4 \times 10^{7} \mathrm{~K}$
 

Question 40 .
Total energy radiated by Sun is about
(a) $3.6 \times 10^{28} \mathrm{Js}^{-1}$
(b) $3.8 \times 10^{28} \mathrm{Js}^{-1}$
(c) $3.8 \times 10^{26} \mathrm{Js}^{-1}$
(d) $3.8 \times 10^{23} \mathrm{Js}^{-1}$.
Answer:
(c) $3.8 \times 10^{26} \mathrm{Js}^{-1}$
 

II. Fill in the blanks:

Question $1 .$
Cathode rays are discovered by_______
Answer:
J.J. Thomson.
 

Question $2 .$
Positive rays discovered by_______
Answer:
Goldstein.
 

Question 3 .
The chargeless particles are called neutron, it was discovered by_______
Answer:
James Chadwick.
 

Question $4 .$
Ernest Rutherford explained that the mass of an atom is concentrated in its central part called_______
Answer:
Nucleus.
 

Question $5 .$
The radioactive elements emit harmful radiations are _______, _______, ______ rays.
Answer:
alpha, beta, gamma.
 

Question $6 .$
_______is an spontaneous process.
Answer:
Natural radioactivity.
 

Question $7 .$
The element whose atomic number is more than 83 undergoes_______
Answer:
spontaneous process.
 

Question $8 .$
_______radioactive material is present in the ore of pitchblende.
Answer:
Uranium.

Question $9 .$
_______are the example of artificial (or) man-made radioactive elements.
Answer:
Boron, Aluminium.
 

Question $10 .$
The element whose atomic number is less than 83 undergoes_______
Answer:
induced radioactivity.
 

Question $11 .$
_______is an controlled manner.
Answer:
Artificial radioactivity.
 

Question $12 .$
Spontaneous radioactivity is also known as_______
Answer:
Natural radioactivity.
 

Question $13 .$
One Curie is equal to_______ disintegrations per second.
Answer:
$3.7 \times 10^{10}$
 

Question $14 .$
One Rutherford (Rd) is equal to_______ disintegrations per second.
Answer:
$10^{6}$

Question 15 .
The radioactive displacement law is framed by_______
Answer:
Soddy and Fajan.
 

Question $16 .$
During the $\alpha$ decay process, the atomic number is by 2 and the mass number is decreases by_______
Answer:
decreases, 4 .
 

Question $17 .$
In $\beta$-decay the atomic number increases by_______ unit and mass number_______
Answer:
One, remains the same.
 

Question $18 .$
In $\alpha$ radiation, the charge of each alpha particle is_______
Answer:
$+2 \mathrm{e}$.
 

Question $19 .$
In $\gamma$ radiation, the charge of each gamma particle is_______
Answer:
Zero.
 

Question $20 .$
In radioactive radiation, which one is travel with the speed of light_______
Answer:
Gamma radiation.

Question $21 .$
$z^{Y^{A}} \rightarrow z_{-2} Y^{A-4}+X ;$ Then $\mathrm{X}$ is_______
Answer:
${ }_{2} \mathrm{He}^{4}(\alpha$ decay)
 

Question $22 .$
$z^{Y^{A}} \rightarrow_{z} Y^{A+X} ;$ Then $\mathrm{X}$ is_______
Answer:
$\gamma$ decay.
 

Question $23 .$
The average energy released in each fission process in about_______
Answer:
$3.2 \times 10^{-11} \mathrm{~J}$.
 

Question $24 .$
Fissionable material is a radioactive element, which undergoes fission in a sustained manner when it absorbs a_______
Answer:
Neutron.
 

Question $25 .$
_______isotope is used to detect the presence of block in blood vessels and also used for the effective functioning of the heart.
Answer:
$\mathrm{Na}^{24}-$ Radio sodium.

Question $26 .$
_______is used to cure goitre.
Answer:
Radio Iodine $-I^{131}$
 

Question $27 .$
_______is used to diagnose anaemia and also to provide treatment for the same.
Answer:
Radio - iron $\left(\mathrm{Fe}^{59}\right)$
 

Question $28 .$
Radio cobalt $\left(\mathrm{Co}^{60}\right)$ and radio gold $\left(\mathrm{Au}^{198}\right)$ are used in the treatment of_______
Answer:
Skin cancer.
 

Question $29 .$
_______are used to sterilize the surgical devices as they can kill the germs and microbes.
Answer:
Radiations.
 

Question 30 .
The age of the earth, fossils, old paintings and monuments can be determined by_______ technique.
Answer:
Radiocarbon dating.
 

Question 31 .
When the body is exposed to about $600 \mathrm{R}$, it leads to_______
Answer:
Death.

Question $32 .$
Radioactive materials should be kept in a thick - walled container of_______
Answer:
Lead.
 

Question $33 .$
_______is used to remove the heat produced in the reactor core, to produce steam.
Answer:
Coolant.
 

Question $34 .$
The abbreviation of BARC is_______
Answer:
Bhabha Atomic Research Centre.
 

Question 35 .
India's 1 st nuclear power station is_______
Answer:
Tarapur Atomic Power Station.

Question $36 .$
The first nuclear reactor built in India was_______
Answer:
Apsara.
 

Question $37 .$
The total nuclear power operating sites in India is_______
Answer:
7
 

Question $38 .$
The energy released in a nuclear fission process is about_______
Answer:
$200 \mathrm{Mev} .$
 

Question $39 .$
The number of $n^{1}$ released on an average per fission is_______
Answer:
$2.5$.
 

Question $40 .$
A hydrogen bomb is based on the principle of_______
Answer:
Nuclear fusion.
 

III. Match the following
Question 1.

Answer:
1. (b) spontaneous process
2. (d) induced process
3. (a) $3.7 \times 10^{10}$ decay $/$ second
4. (c) $10^{6}$ decay $/$ second
 

Question $2 .$

Answer:
1. (b) $+2 \mathrm{e}$
2. (d) zero
3. (a) $\gamma$ ray
4. (e) $\alpha$ ray

Question 3 .

Answer:
1. (e) ${ }_{1} \mathrm{H}^{2}$
2. (d) ${ }_{1} \mathrm{H}^{1}$
3. (b) ${ }_{1} \mathrm{H}^{3}$
4. (c) ${ }_{2} \mathrm{H}^{4}$
5. (a) $-1^{e^{0}}$
 

Question $4 .$

Answer:
1. (d) Hiroshima
2. (c) Nagasaki
3. (a) fusion bomb
4. (b) fission bomb
 

Question $5 .$

Answer:
1. (c) diagnose anaemia
2. (a) treatment of skin diseases
3. (d) treatment of skin cancer
4. (b) smoke detector
 

IV. Arrange the following in the correct sequence
Question $1 .$
Arrange $\alpha, \beta, \gamma$ rays in ascending order, on the basis of their penetrating power?
Answer:
Ascending order:
- Alpha $(\alpha)$
- Beta $(\beta)$
- Gamma ( $\gamma)$
 

Question $2 .$
Arrange in ascending and descending order, on the basis of their Ionisation power.
Alpha $(\alpha)$, Beta $(\beta)$, Gamma $(\gamma)$
Answer:
1. Ascending order: Gamma $(\gamma)$, Beta $(\beta)$, Alpha $(\alpha)$
2. Descending order: Alpha $(\alpha)$, Beta $(\beta)$, Gamma $(\gamma)$
 

Question $3 .$
Arrange in ascending and descending order, on the basis of their biological effect.
Alpha $(\alpha)$, Gamma ( $\gamma)$, Beta ( $\beta$ )
Answer:
1. Ascending order: Alpha $(\alpha)$, Beta $(\beta)$, Gamma $(\gamma)$
2. Descending order: Gamma $(\gamma)$, Beta $(\beta)$, Alpha $(\alpha)$.

V. Numerical Problems
Question $1 .$
${ }_{92} U^{238}$ emits $8 \alpha$ particles and $6 \beta$ particles. What is the neutron / proton ratio in the product nucleus?
Solution:
$$
{ }_{92} \mathrm{U}^{238} \stackrel{-8 \alpha}{\longrightarrow} 76 \mathrm{X}^{206}+8{ }_{2} \mathrm{He}^{4}(8 \alpha \text { decay })
$$
The result of $\alpha$ decay
$$
\begin{aligned}
{ }_{76} \mathrm{X}^{206} \stackrel{-6 \beta}{\longrightarrow}{ }_{82} \mathrm{Y}^{206}+6 \\
\text { Number of proton } &=82 \\
\text { Number of neutron } &=124 \\
\text { The ratio in the product nucleus } &=\frac{124}{82} \\
\frac{\text { neutron }}{\text { proton }} &=\frac{62}{41}
\end{aligned}
$$

Question $2 .$
The element with atomic number 84 and mass number 218 change to another element with atomic number 84 and mass number 214 . The number of $\alpha$ and $\beta$ particles emitted are respectively?
Solution:
${ }_{84} \mathrm{X}^{218} \stackrel{\alpha \text { decay }}{\longrightarrow}{ }_{82} \mathrm{Y}^{214}+x_{2} \mathrm{He}^{4}$
${ }_{82} \mathrm{Y}^{214} \longrightarrow \mathrm{Y}^{214}+y_{2} \mathrm{e}^{0}$
Number of alpha decay, $x=1$
Number of beta decay, $y=2$.

Question $3 .$
The number of $\alpha$ and $\beta$ particles emitted in the nuclear reaction ${ }_{90} \mathrm{Th}^{228} \longrightarrow_{83} \mathrm{Bi}^{12}$ are respectively.
Solution:
${ }_{90} \mathrm{Th}^{228} \stackrel{4 \alpha}{\longrightarrow}{ }_{82} \mathrm{Xi}^{212}+x \times \mathrm{He}^{4}$
${ }_{82} \mathrm{X}^{212} \longrightarrow{ }_{83} \mathrm{Bi}^{212}+y_{-1} \mathrm{e}^{0}$
Number of $\alpha$ decay, $x=4$
Number of $\beta$ decay, $y=1$.
 

VI. Assertion and Reason Type Questions
(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 Assertion is true, but the reason is false.
(d) If Assertion is false, but the reason is true.
(e) If the Assertion and reason both are false.
 

Question $1 .$
Assertion: All the radioactive element are ultimately converted in lead.
Reason: All the elements above lead are unstable.
Answer:
(c) If Assertion is true, but the reason is false.
Explanation: When they are converted into a lead, the emission is stopped because the nucleus of lead is stable (or lead is most stable elements in radioactive series)

Question $2 .$
Assertion: Among the alpha, beta and gamma-ray a particle has maximum penetrating power. Reason: The alpha particle is heavier than beta and gamma rays.
Answer:
(e) If the Assertion and reason both are false.
Explanation: The penetrating power is maximum in case of gamma rays because gamma rays are electromagnetic radiation of very small wavelength.
 

Question $3 .$
Assertion: The ionising power of $\beta$ - particle is less compared to $\alpha$ - particles but their penetrating power is more.
Reason: The mass of $\beta$-particle is less than the mass of $\alpha$-particle
Answer:
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the
assertion.
Explanation: $\beta$ - particle being emitted with very high speed compared to $\alpha$ - particle. Due to this reason, their loss of energy is very slow and they can penetrate the medium through a sufficient depth.
 

Question $4 .$
Assertion: Neutrons penetrate matter more readily as compared to protons.
Reason: Neutrons are slightly more massive than protons.
Answer:
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.

Explanation: Neutron is about $0.1 \%$ more massive than a proton. But the unique thing about the neutron is that while it is heavy, it has no charge (it is neutral). This lack of charge gives it the ability to penetrate matter without interacting as quickly as the beta particles or alpha particles.

Question $5 .$
Assertion: ${ }_{z} X^{A}$ undergoes a decays and the daughter product is $z_{z-2} Y^{A-4}$
Reason: In $\alpha$-decay, the mass number decreases by 4 and atomic number decreases by.
Answer:
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.
Explanation: ${ }_{z} \mathrm{X}^{\mathrm{A}} \longrightarrow_{z-2} \mathrm{X}^{\mathrm{A}-4}+{ }_{2} \mathrm{He}^{4}$ ( $\alpha$. decay)
 

Question $6 .$
Assertion: Moderator is used to slowing down the high energy neutrons to provide slow neutrons.
Reason: Cadmium rods are used as control rods.
Answer:
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.

Explanation: Graphites and heavy water are commonly used moderators. This helps in moderator to slow down the fast neutrons.
 

Question $7 .$
Assertion: Alpha, beta and gamma radiations are emitted.
Reason: Nuclear fission process can be performed at room temperature.
Answer:
(a) If both the assertion and the reason are true and the reason is the correct explanation of the
assertion.
Explanation: At room temperature, the nuclear fission process can perform breaking up of heavier nucleus into two smaller nuclei. In this process to emitted the alpha, beta and gamma radiations.
 

Question 8.
Assertion: An enormous amount of energy is released which is called stellar energy.

Reason: Fusion reaction that takes place in the cores of the Sun and other stars.
Answer:
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.

Explanation: The stars like our Sun emit a large amount of energy in the form of light and heat. This energy is termed as the stellar energy.
 

Question $9 .$
Assertion: Artificial radioactivity is a controlled process.
Reason: It is a spontaneous process - natural radioactivity.
Answer:
(b) If both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.

Explanation: Artificial radioactivity is a controlled process. It is an induced process and man-made radioactivity.
 

Question $10 .$
Assertion: Gamma rays, penetrates through materials most effectively.
Reason: Gamma rays, which have the shortest wavelengths of all electromagnetic radiation.
Answer:
(a) If both the assertion and the reason are true and the reason is the correct explanation of the assertion.

Explanation: Gamma rays, which have the shortest wavelengths of all electromagnetic radiation. This is a reason they can penetrate through materials most effectively.
 

VII. Answer the following questions
Question $1 .$
Define 'Radioactivity'.
Answer:
The phenomenon of nuclear decay of certain elements with the emission of radiations like alpha, beta, and gamma rays is called 'radioactivity'.
 

Question $2 .$
By whom radioactivity is detected in pitchblende?
Answer:
Marie curie and Purie curie.

Question $3 .$
Define 'Artificial Radioactivity'.
Answer:
The phenomenon by which even light elements are made radioactive, by artificial or induced methods, is called 'Artificial radioactivity' or 'Man - made radioactivity'.
 

Question $4 .$
Define 'One curie'.
Answer:
It is defined as the quantity of a radioactive substance which undergoes $3.7 \times 10^{10}$ disintegrations in one second. This is actually close to the activity of $1 \mathrm{~g}$ of radium 226 .
Curie $=3.7 \times 10^{10}$ disintegrations per second.
 

Question $5 .$
In which elements artifical radioactivity is induced?
Answer:
Boron and aluminum
 

Question 6.
What is alpha decay (a decay)? give an example.
Answer:
A nuclear reaction in which an unstable parent nucleus emits an alpha particle and forms a stable daughter nucleus is called 'alpha decay'.
E.g. Decay of uranium $\left(\mathrm{U}^{238}\right)$ to thorium $\left(\mathrm{Th}^{234}\right)$ with the emission of an alpha particle.
${ }_{92} \mathrm{U}^{238} \rightarrow \infty \mathrm{Th}^{234}+{ }_{2} \mathrm{He}^{4}(\alpha$ - decay).

Question 7 .
What is beta decay ( $\beta$ decay)? Give an example?
Answer:
A nuclear reaction, in which an unstable parent nucleus emits a beta particle and forms a stable daughter nucleus, is called 'beta decay'.
E.g. Beta decay of phosphorous.
${ }_{15} \mathrm{P}^{32} \rightarrow{ }_{16} \mathrm{~S}^{32}+-1 \mathrm{e}^{0}(\beta-$ decay $)$
 

Question $8 .$
What is gamma decay ( $\gamma$ decay)?
Answer:
In a $\gamma$ - decay, only the energy level of the nucleus changes. The atomic number and mass number of the radioactive nucleus remain the same.
 

Question $9 .$
State the value of Roentgen in terms of Coulomb.
Answer:
Roentgen $=2.58 \times 10^{-4}$ Coulomb in $/ \mathrm{kg}$ of air.
 

Question 10 .
Define 'nuclear fission' Give an example.
Answer:
The process of breaking (splitting) up of a heavier nucleus into two smaller nuclei with the release
of a large amount of energy and a few neutrons are called 'nuclear fission'.
E.g. Nuclear fission of a uranium nucleus ( $\left.\mathrm{U}^{235}\right)$
$92^{\mathrm{U}}{ }^{\mathrm{U} 26}+0 \mathrm{n}^{1} \rightarrow 56 \mathrm{Ba}^{141}+36 \mathrm{Kr}^{92}+30 \mathrm{n}^{1}+\mathrm{Q}($ energy $)$

Question $11 .$
Define 'Nuclear fusion' Give an example.
Answer:
The process in which two light nuclei combine to form a heavier nucleus is termed as 'Nuclear fusion'.
E.g. $\mathrm{H}^{2}+{ }_{1} \mathrm{H}^{2} \rightarrow_{2} \mathrm{He}^{4}+\mathrm{Q}($ Energy $)$
 

Question $12 .$
Write down the types of the nuclear reactor.
Answer:
Breeder reactor, fast breeder reactor, pressurized water reactor, pressurized heavy water reactor, boiling water reactor, water - cooled reactor, gas - cooled reactor, fusion reactor and thermal reactor are some types of nuclear reactors, which are used in different places worldwide.
 

Question $13 .$
What is the safe limit of receiving radioactive radiations?
Answer:
$100 \mathrm{~m} \mathrm{R}$ per week
 

VIII. Answer in the details:
Question $1 .$
Explain the principle and working of an atom bomb?
Answer:
Atom bomb:
(i) The atom bomb is based on the principle of the uncontrolled chain reaction. In an uncontrolled chain reaction, the number of neutrons and the number of fission reactions multiply almost in a geometrical progression.
(ii) This releases a huge amount of energy in a very small time interval and leads to an explosion.

Structure:
(i) An atom bomb consists of a piece of fissile material whose mass is subcritical. This piece has a cylindrical void.
(ii) It has a cylindrical fissile material which can fit into this void and its mass is also subcritical. When the bomb has to be exploded, this cylinder is injected into the void using a conventional explosive.
(iii) The two pieces of fissile material join to form the supercritical mass, which leads to an explosion. During this explosion, a tremendous amount of energy in the form of heat, light and radiation is released.
(iv) A region of very high temperature and pressure is formed in a fraction of a second along with the emission of hazardous radiation like y rays, which adversely affect the living creatures. This type of atom bombs was exploded in 1945 at Hiroshima and Nagasaki in Japan during World War II.
 

Question $2 .$
State and define the units of radioactivity.
Answer:
Curie : It is the traditional unit of radioactivity. It is defined as the quantity of a radioactive substance which undergoes $3.7 \times 10^{10}$ disintegrations in one second. This is actually close to the activity of lg of radium $226.1$ curie $=3.7 \times 10^{10}$ disintegrations per second.

Rutherford (Rd) : It is another unit of radioactivity. It is defined as the quantity of a radioactive substance, which produces $10^{6}$ disintegrations in one second.
$1 \mathrm{Rd}=10^{6}$ disintegrations per second.
Becquerel (Bq): It is the SI unit of radioactivity is becquerel. It is defined as the quantity of one disintegration per second.
Roentgen $(R)$ : It is the radiation exposure of $\gamma$ and x-rays is measured by another unit called roentgen. One roentgen is defined as the quantity of radioactive substance which produces a charge of $2.58 \times 10^{-4}$ coulomb in $1 \mathrm{~kg}$ of air under standard conditions of pressure, temperature and humidity.
 

Question $3 .$
Write down the features of nuclear fission and nuclear fusion.
Answer:

Question $4 .$
Write down the medical and industrial application of radioisotopes?
Answer:
1. Radio sodium $\left(\mathrm{Na}^{24}\right)$ is used for the effective functioning of the heart.
2. Radio - Iodine $\left(\mathrm{I}^{131}\right)$ is used to cure goitre.
3. Radio - Iron is $\left(\mathrm{Fe}^{59}\right)$ is used to diagnose anaemia and also to provide treatment for the same.
4. Radio Phosphorous $\left(\mathrm{P}^{32}\right)$ is used in the treatment of skin diseases.
5. Radio Cobalt $\left(\mathrm{Co}^{60}\right)$ and radio - gold $\left(\mathrm{Au}^{198}\right)$ are used in the treatment of skin cancer.
6. Radiations are used to sterilize the surgical devices as they can kill the germs and microbes.
7. Radio cobalt $\left(\mathrm{Co}^{60}\right)$ and radio - gold $\left(\mathrm{Au}^{198}\right)$ are used in the treatment of skin cancer.
8. Radiations are used to sterilize the surgical devices as they can kill the germs and microbes.
 

Question $5 .$
Write a note about stellar energy.
Answer:
The stars like our Sun emit a large amount of energy in the form of light and heat. This energy is termed as the stellar energy. Where does this high energy come from? All-stars contain a large
amount of hydrogen. The surface temperature of the stars is very high which is sufficient to induce fusion of the hydrogen nuclei.
Fusion reaction that takes place in the cores of the Sun and other stars results in an enormous amount of energy, which is called as 'stellar energy'. Thus, nuclear fusion or thermonuclear reaction is the source of light and heat energy in the Sun and other stars.
 

IX. Additional HOT Questions:

Question $1 .$
Why is neutron so effective as bombarding particle?
Answer:
A neutron carries no charge. It easily penetrates even a heavy nucleus without being repelled or attracted by nucleus and electrons. So it serves as an ideal projectile for starting a nuclear reaction.
 

Question 2.
Is there any difference between electron and a beta particle.
Answer:
Basically, there is no difference between an electron and a beta particle. $\beta$ particle is the name given to an electron emitted from the nucleus.
 

Question $3 .$
Why are the control rods made of cadmium?
Answer:
Cadmium has high cross - section for the absorption of neutrons.
 

Question $4 .$
Name two radioactive elements that are not found in observable quantities why is it so?
Answer:
Tritium and Plutonium are two radioactive elements that are not found in observable quantities in the universe.
It is because half-life period of each of two elements is very short compared to the age of the universe.