6. Nuclear Physics

I. Choose the correct answer.

1. Man – made radioactivity is also known as _____.

(a) Induced radioactivity
(b) Spontaneous radioactivity
(c) Artificial radioactivity
(d) (a) & (c).

2. Unit of radioactivity is:

(a) roentgen
(b) curie
(c) becquerel
(d) all the above

3. Artificial radioactivity was discovered by _____.

(a) Becquerel
(b) Irene Curie
(c) Roentgen
(d) Neils Bohr.

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

5._____ isotope is used for the treatment of cancer.

(a) Radio Iodine
(b) Radio Cobalt
(c) Radio Carbon
(d) Radio Nickel.

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

7._____ aprons are used to protect us from gamma radiations.

(a) Lead oxide             (b) Iron
(c) Lead                      (d) Aluminium.

8. Which of the following statements is / are correct?
(i) α particles are photons
(ii) Penetrating power of γ radiation is very low
(iii) Ionization power is maximum for α rays
(iv) Penetrating power of γ radiation is very high

(a) (i) & (ii) are correct
(b) (ii) & (iii) are correct
(c) (iv) only correct
(d) (iii) & (iv) are correct.

9. Proton-Proton chain reaction is an example of:

(a) Nuclear fission
(b) α – decay
(c) Nuclear fusion
(d) β – decay

10. In the nuclear reaction, the value of A & Z.

(a) 8, 6
(b) 8, 4
(c) 4, 8
(d) cannot be determined with the given data.

11. Kamini reactor is located at _____.

(a) Kalpakkam
(b) Koodankulam
(c) Mumbai
(d) Rajasthan.

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

II. Fill in the blanks

1. One roentgen is equal to 3.7 × 1010 disintegrations per second?

2. Positron is an antiparticle of electron.

3. Anaemia can be cured by Radio iron (Fe59) isotope.

4. Abbreviation of ICRP International Commission on Radiological Protection.

5. Roentgen is used to measure the exposure rate of radiation in humans.

6. Gamma ray has the greatest penetration power.

7.  ZYA → Z+1YA + X ; Then, X is beta.

8. ZXA → ZYA This reaction is possible in Gamma (γ) decay

9. The average energy released in each fusion reaction is about 3.84 × 10-12J.

10. Nuclear fusion is possible only at an extremely high temperature of the order of 107 to 109 K.

11. The radioisotope of phosphorous (P – 32). helps to increase the productivity of crops.

12. If radiation exposure is 100 R, it may cause fatal disease.

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

1. Plutonium -239 is a fissionable material.
          Answer:   True.

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.

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 (3.2 × 10-11 J) process is more than the average energy released in fusion (3.84 × 10-12 J).

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 Pu239 and U233. Only fissile materials are used in the fuel of a nuclear reactor.

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

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

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

IV. Match the following

1. 

1. BARC

(c) Mumbai

2. India’s first atomic power station

(d) Tarapur

3. IGCAR

(a) Kalpakkam

4. The first nuclear reactor in India

(b) Apsara

2.

1. Fuel

(d) Uranium

2. Moderator

(c) Graphite

3. Coolant

(b) heavy water

4. Shield

(a) lead

3.

1. Soddy Fagan

(b) Displacement law

2. Irene Curie

(d) Artificial Radioactivity

3. Henry Becquerel

(a) Natural radioactivity

4. Albert Einstein

(c) Mass energy equivalence

4.

1. Uncontrolled fission Reaction

(d) Atom bomb

2. Fertile material

(c) Breeder reactor

3. Controlled fission Reaction

(b) Nuclear Reactor

4. Fusion reaction

(a) Hydrogen Bomb

5.

1. Co – 60

(c) Leukaemia

2. I – 13

(d) Thyroid disease

3. Na – 24

(b) Function of Heart

4. C – 14

(a) Age of fossil

V. Arrange the following in the correct sequence

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.

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

1. Spontaneous process : Natural Radioactivity, Induced process: Artificial radioactivity.

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

3. Increasing crops : Radio phosphorous, Effective functioning of heart: Radio sodium (Na24).

4. Deflected by electric field : α ray, Null Deflection: γ ray (Gamma – ray).

VII. Numerical Problems

1. 88Ra226 experiences three α - decay. Find the number of neutrons in the daughter element.

132 Neutrons.

2. A cobalt specimen emits induced radiation of 75.6 millicurie per second. Convert this disintegration in to becquerel (one curie = 3.7 × 1010 Bq)

Solution:
Cobalt specimen emits induced radiation = 75.6 millicurie per second
(1 curie = 3.7 × 1010 Bq)
So 75.6 millicurie = 75.6 × 103 × 1 curie
= 75.6 × 10-3 × 3.7 × 1010 Bq
= 279.72 × 107
= 2.7972 × 109 Bq
75.6 millicurie per second is equivalent to 2.7972 × 109 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.

1. Assertion: A neutron impinging on U235, 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.

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

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.

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)

1. Who discovered natural radioactivity?

Henri Becquerel

2. Which radioactive material is present in the ore of pitchblende?

Uranium

3. Write any two elements which are used for inducing radioactivity?

Boron and Aluminium.

  1. Alpha particle and neutron.

4. Write the name of the electromagnetic radiation which is emitted during a natural radioactivity.

Gamma rays

5. If A is a radioactive element which emits an α - particle and produces 104Rf259. Write the atomic number and mass number of the element A.

106Sg263 Atomic number of A = 106, Mass number of A = 263.

6. What is the average energy released from a single fission process?

3.2 × 10-11 J.

7. Which hazardous radiation is the cause for the genetic disorders (or) effect?

Radioactive radiations

8. What is the amount of radiation that may cause the death of a person when exposed to it?

When the body is exposed to about 600 R, it leads to death.

9. When and where was the first nuclear reactor built?

The first nuclear reactor was built in 1942 in Chicago, USA.

10. Give the SI unit of radioactivity.

Becquerel

11. Which material protects us from radiation?

Lead

X. Answer the following questions in a few sentences.

1. Write any three features of natural and artificial radioactivity.

Natural radioactivity

Artificial radioactivity

1. Emission of radiation due to the self-disintegration of a nucleus.

1. Emission of radiation due to the disintegration of a nucleus through the induced process.

2. Alpha, Beta and Gamma radiations are emitted.

2. Mostly elementary particles such as neutron, positron, etc. are emitted.

3. It is a spontaneous process.

3. It is an induced process.

2. Define critical mass.

The minimum mass of fissile material necessary to sustain the chain reaction is called ‘critical mass (mc). It depends on the nature, density and the size of the fissile material.

3. Define One roentgen.

One roentgen is defined as the quantity of radioactive substance which produces a charge of 2.58 × 10-4 coulomb in 1 kg of air under standard conditions of pressure, temperature and humidity.

4. State Soddy and Fagan’s displacement law.

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.

5. Give the function of control rods in a nuclear reactor.

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.

6. In Japan, some of the newborn children are having congenital diseases. Why?

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.

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?

X – rays have a destructive effect on living tissue. When the human body is exposed to 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.

8. What is stellar energy?

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.

9. Give any two uses of radioisotopes in the field of agriculture?

  • The radioisotope of phosphorus (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.

1. Explain the process of controlled and uncontrolled chain reactions.

(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. 

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

 

Properties

α rays

β rays

γ rays

What are they?

Helium nucleus (2He4)

consisting of two protons

and two neutrons.

They are electrons

(–1e0), basic elementary particle in

all atoms.

They are electromagnetic waves consisting of photons.

Charge

Positively charged particles. Charge of each alpha particle = +2e

Negatively charged particles. Charge of each beta particle = -e

Neutral particles. Charge of each gamma particle = zero

Ionising Power

100 time greater than β rays and 10,000 times greater than γ rays

Comparatively low

Very less ionization power

Penetrating power

Low penetrating power (even stopped by a thick paper)

Penetrating power is greater than that of α rays. They can penetrate through a thin metal foil.

They have a very high penetrating power greater than that of β rays. They can penetrate through thick metal blocks.

Effect of an electric and magnetic field

Deflected by both the fields. (in accordance with Fleming’s left-hand rule)

Deflected by both the fields, but the direction of deflection is opposite to that for alpha rays. (in accordance with Fleming’s left-hand rule)

They are not deflected by both the fields.

Speed

Their speed ranges from 1/10 to 1/20 times the speed of light.

Their speed can go up to 9/10 times the speed of light.

They travel with the speed of light.

3. What is a nuclear reactor? Explain its essential parts with their functions.

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

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.

Determine the number of alpha decay:
208 = 232 – 4X
Solve for X
232 – 4X – 232 = 208 – 232 ( substract 232 from both sides)
–4X = –24
– X = – 6
    X = 6.
This means that this progress undergoes 6 α-decays, which means 6 nuclei of He have been emitted. Determine the number of Beta decay is four.

2.  ‘X – rays should not be taken often’. Give the reason.

  • Radiation does involve in X – rays tests and isotope scans (in nuclear medicine) are too low to cause immediate hazardous effects.
  • If should be taken often, X – ray radiation from medical examinations though slightly increases one’s risk for cancer which can occur year or decades after X-ray exposure.

3. Cell phone towers should be placed far away from the residential area. why?

Living near a cell phone tower is not healthy. There is multiple health risks associated with living near a cell phone tower.

  1. Cell phone towers communicate by use pulsed microwave signals (radiofrequency radiation) with each other.
  2. That is the reason cell phone towers should be placed far away from the residential area.