PHY/VI/10 Student's Copy
2 0 1 8
6th Semester
PHYSICS
TENTH PAPER
Nuclear Physics—II
Revised
Full Marks 75
Time 3 hours
PART A—OBJECTIVE
Marks 25
The figures in the margin indicate full marks for the questions
SECTION—A
Marks 10
Tick the correct answer in the brackets provided 1×10=10
1. In the semiempirical binding energy formula of a nucleus, which of the
following energies is positive?
Asymmetry energy Volume energy
Coulomb energy Surface energy
2. Which of the following pairs are mirror nuclei?
6
C13 and 6
C14 7
N14 and 6
C14
4
Be7 and 3
Li7 5
B10 and 4
Be8
3. The mass of a deuteron 2 × 01335 a.m.u., mass of a proton
=1× 00728 a.m.u. and mass of a neutron =1× 00866 a.m.u. The
binding energy of a deuteron is nearly [Given 1 a.m.u. 931 MeV]
2·23 MeV 1·22 MeV
1·12 MeV 28·1 MeV
4. The decay constant is defined as the reciprocal of time during which the
number of atoms of a radioactive substance falls to
1
2 of its original value 13
of its original value
1
4 of its original value 1
e of its original value
/491 1 Contd.
5. According to nuclear shell model, the total angular momentum of 8
O16 is
5
2 3
2
1
2 zero
6. The threshold energy is applicable only for
exoergic reactions endoergic reactions
exothermic reactions all nuclear reactions
7. Which of the following particles can be accelerated in a cyclotron?
Electron Neutron
Proton All of the above
8. If 2000 particles are passing through the GM counter in a given time and
1500 are recorded in the same time, then efficiency of the counter is
75% 50%
30% 15%
9. The primary cosmic radiations approaching the earth's atmosphere
contains mainly
protons and a-particles
electrons and a-particles
protons and p-mesons
electrons, positrons and photons
10. Which of the following quarks is positively charged?
Strange Bottom
Charm Down
SECTION—B
Marks 15
Answer the following questions 3×5=15
1. Mention at least three important properties of nuclear forces.
2. Show that the binding energy per nucleon for a-particle of Helium nucleus

He4 is 7·04 MeV. Given masses mp =1× 007276 a.m.u., mn =1× 008665
a.m.u., Ma 4 × 001506 a.m.u. and 1 a.m.u. 931 MeV.
3. Calculate the Q-value of the following nuclear reaction in MeV
3
7
1
1
2
4
2
Li H He He4. Given that masses of 3
Li7 7 × 018222 a.m.u.,
1
H1 =1× 008144 a.m.u. and 2
He4 4 × 003873 a.m.u. Comment whether the
energy is released or absorbed in this reaction.
PHY/VI/10 2 Contd.
4. What is the main limitation of a cyclotron and how this problem is solved in
synchrotron and synchrocyclotron?
5. What are hadrons? Explain with examples how these are classified based on
quark structure.
PART B—DESCRIPTIVE
Marks 50
The figures in the margin indicate full marks for the questions
1. Define isotope, isobar and isotone and give example of each. 3
Show that the nuclear density is constant and of the order of
1017 kg.m-3 for all nuclei. Mention a celestial object having density of
same order.
Write a short note on nuclear stability with reference to
neutron-proton ratio. 3
OR
Define binding energy of a nucleus and write its expression. Explain
why the surface effect reduces the binding energy by Es bA2/3,
where A is the mass number and b is a constant.
"The electrostatic repulsion between each pair of protons in a nucleus
also contributes towards reducing its binding energy." Explain this
statement and find the expression of Coulomb energy EC. 2
Draw a curve of binding energy per nucleon in MeV as a function of
mass number A and discuss its significance in explaining nuclear
fission and fusion.
2. Derive the exponential decay law of a radioactive substance. Hence
show that the half-life T 0 × 693l, where l is the decay constant.

Define mean-life of a radioactive substance and hence show that
Tm =1× 44T.
OR
Discuss three different types of b-decay with representative reactions
and examples. 6
What conservation laws must be followed by g-ray emission from a
radioactive substance? What do you mean by nuclear isomerism?
3. State the main assumptions of nuclear shell model and mention the
experimental evidences in favour of it. 3
PHY/VI/10 3 Contd.
Based on the level schemes of single-particle shell model, show that
the total angular momentum of the nucleus of 8
O17 is 5
2. 2
What do you mean by threshold energy and Q-value of a nuclear
reaction? Establish the relation between these.
OR
Explain how the Bohr-Wheeler theory accounts for various properties
of nuclear fission. 5
What is fusion reaction? Give an example. Why is it called
thermonuclear reaction? 2
Write a short note on nuclear reactor. 3
4. Describe the construction and working of a linear accelerator. What
are its limitations?
Discuss the construction and working of a proportional counter. Why
is the device so named?
OR
Write short notes on any two of the following 5×2=10
Betatron
Synchrocyclotron
Geiger-Müller counter
Wilson cloud chamber
5. What are primary and secondary cosmic rays? Discuss 'east-west
effect' to explain that primary cosmic rays carry mainly positively
charged particles.
Describe with schematic diagrams, Bhabha's theory of cosmic-ray
showers. 5
OR
What are leptons and anti-leptons? Mention the names of all leptons
with their charge and lepton numbers. Show that the lepton numbers
remain conserved in the following neutron decay process
n p e ve
where p is proton, e is electron and ve is anti-neutrino.
What do you mean by baryon number hypercharge and
strangeness Mention the relation among those and verify the
relation for neutron.