Nuclear physics is a branch of physics that focuses on the study of atomic nuclei and their interactions. It explores the properties and behavior of atomic nuclei, which are the central cores of atoms containing protons and neutrons. This field is crucial for understanding the fundamental forces that govern the behavior of matter at the atomic and subatomic levels.

1. NUCLEAR PHYSICS

2. INDEX
1. What is Nuclear Physics?
2. Nucleus
3. Nuclear Force
4. Mass Defect
5. Nuclear Binding Energy
6. Nuclear Reaction
7. Nuclear Fission
8. Nuclear Fusion
9. Radioactivity
10.Radioactive Decay Lay

3. What is Nuclear Physics?
Nuclear physics is the field of physics that studies atomic nuclei and
the constitutions and interactions, in addition to the study of other forms
of nuclear matter.
Nuclear physics should not be confused with atomic physics, which
studies the atom as a whole, including its electrons.

4. Nucleus
The entire positive charge and nearly the
entire mass of atom is concentrated is a
very small space called the nucleus of an
atom.
The nucleus consists of protons and
neutrons. They are called nucleons

5. Nuclear Force
The force acting inside the nucleus or acting between nucleons is called
nuclear force.
Nuclear forces are the strongest forces in nature.
It is a very short range attractive force.
It is non-central and non-conservative force.
It is independent of charge.
It is 100 times that of electrostatic force and 1038 times that of gravitational
force.
According to the Yukawa, the nuclear force acts between the nucleons due to
continuous exchange of meson particles.

6. Mass Defect
The difference between the sum of masses of all nucleons (M) and mass of
the nucleus (m) is called mass defect.
Mass defect (𝚫m) = M - m = [Zmp+ (A - Z)mn - mN]
Mass Energy Relation
Einstein showed that mass is another form of energy and can convert mass
energy into other forms of energy.
Einstein - mass energy, E=mc2

7. Mass Defect
Nuclear Binding Energy
The minimum energy required to separate the nucleons upto an infinite
distance from the nucleus is called nuclear binding energy.
Binding energy, Eb - [Zmp+ (A - Z)mn - mN]c2
Packing Fraction (P)
The larger the value of packing friction, greater is the stability of the
nucleus.

8. Binding Energy Curve

9. Some features of this curve are given below as
1. Nuclei having mass number 50 to 80 are most stable.
2. Nuclei having mass number more than 80, the average binding energy
per nuclei decreases. The nuclei of heavier atoms beyond 83 Bi 209 are
radioactive.
3. Nuclei having mass number below 20 are comparatively less stable.
4. Even-Even nuclei are more stable than their intermediate neighbours.
The nuclei containing even number of protons and even number of neutrons
are most stable. The nuclei containing odd number of protons and odd
number of neutrons are most unstable.

10. Nuclear Reaction
The process by which the identity of a nucleus is changed when it is
bombarded by an energetic particle is called nuclear reaction. Its general
expression is
Q-Value
It means the difference between the rest mass energy of initial
constituents and the rest mass energy of final constituents of a nuclear
reaction.
Parent nucleus Incident particle Compound nucleus product nucleus daughter nucleus energy
X + a → x → Y + b + Q

11. Nuclear Energy
The energy released during nuclear reaction is nuclear energy Two distinct
ways of obtaining energy from nucleus are as
(1) Nuclear fission
(2) Nuclear fusion
Nuclear Fission
The process of the splitting of a heavy nucleus into two or more lighter
nuclei is called nuclear fission.
When a slow moving neutron strikes with a uranium nucleus ( 91U235 ), it
splits into 56Ba141 and 36Kr92 along with three neutrons and a lot of
energy.
91U235 + 0n1 → 56Ba141 + 36Kr92 + 30n1 + energy

12. Nuclear Chain Reaction
If the particle starting the nuclear fission
reaction is produced as a product and
further take part in the nuclear fission
reaction, then chain of fission reaction
started, which is called nuclear chain
reaction.
Nuclear chain reaction are of two types
1. Controlled chain reaction
2. Uncontrolled chain reaction

13. Nuclear Reactor

14. 1. Fuel Fissionable materials like 91U235 , 92U238 , 94Pu239 are used as
fuel.
2. Moderator Heavy water, graphite and beryllium oxide are used to
slower down fast moving neutrons.
3. Coolant The cold water, liquid oxygen etc are used to remove heat
generated in the fission process.
4. Control rods Cadmium or boron rods are good absorber of
neutrons and therefore used to control the fission reaction.
Notes : Atom bomb's working is based on uncontrolled chain reaction.

15. Nuclear Fusion
The process of combining of two lighter nuclei to form one heavy
nucleus is called nuclear fusion.
When three deuteron nuclei (H) are fused, 21.6 MeV is energy released
and nucleus of helium (He) is formed.
1H² + 1H2 + 1H2 → 2He4 + 1H1 + on¹ + 21.6 MeV
In this process, a large amount of energy is released. Nuclear fusion
takes place at very high temperature approximately about 10 K and at
very high pressure 10" atmosphere. Thus, the energy released during
nuclear fusion is known as thermonuclear energy. Hydrogen bomb is
based on nuclear fusion.
The source of sun's energy is the nuclear fusion taking place in the
interior of sun.

16. Radioactivity
The phenomenon of spontaneous emission of radiations by nucleus of
some elements is called radioactivity.
This phenomenon was discovered by Henry Becquerel in 1896.
Radiations Emitted by a Radioactive Element
Three types of radiations emitted by radioactive elements are
1. 𝛼-rays
2. ꞵ-rays
3. 𝛾-rays

17. S.No Property 𝛼 - particle Ꞵ - particle 𝛾 - particle
1 Nature Helium nucleus Fast moving
electrons
Electromagnetic wave
2 Charge +2e -e zero
3 Rest mass 6.67 x 10-27 kg 9.1 x 10-31 kg zero
4 Speed 1.4 x 107 to
2.2 x 107 ms-1
1 to 99 % of c =
3 x 108 ms-1
c = 3 x 108 ms-1
5 Ionising power 104 102 1
6 Penetrating
power
1 102 104

18. ● When an a-particle is emitted by a nucleus its atomic number
decreases by 2 and mass number decreases by 4.
ZXA → Z + 2YA - 4 + 2He4 + ⊽
● When a B-particle is emitted by a nucleus its atomic number is
increases by one and mass number remains unchanged.
ZXA → Z + 1YA + e- + ⊽
● When a y-particle is emitted by a nucleus its atomic number and
mass number remain unchanged.

19. Radioactive Decay Law
The rate of disintegration of radioactive nuclei at any instant is directly
proportional to the number of radioactive nuclei present in the sample at
that instant.
where, λ is the decay constant.
The number of nuclei present undecayed in the sample at any instant
N = N0 e-λt
where, No is number of nuclei at time t=0 and N is number of nuclei at
time t

20. Half-life of a Radioactive Element
The time in which the half number of nuclei present initially in any
sample decays is called half-life (T) of that radioactive element. Relation
between half-life and disintegration constant is given by

21. Average life or mean life (t) of a radioactive element is the ratio of total
life time of all the nuclei and total number of nuclei present initially in the
sample.
Relation between average life and decay constant,
Relation between half-life and average life, τ = 1.44 T1/2
The number of nuclei left undecayed after n half-lives is given by
where, , here t = total time.
Average Life or Mean Life (τ)

22. The activity of a radioactive element is equal to its rate of
disintegration.
Activity, R =
Activity of the sample after time t, R = Re0e-λt
Its SI unit is Becquerel (Bq).
Its other units are Curie and Rutherford.
1 Curie = 3.7x1010 decay's
1 Rutherford = 10° decay/s
Activity of a Radioactive Element

23. Thank you