2. • What is Nuclear Physics?
• Why is important to study?
• What are the applications?
3. History
1.In the 5th Century BC Democritus et al postulated that matter is made up of indivisible particles known
as atoms.
There was no experimental evidence.
2. In the 19th century John Dalton proposed his atomic theory.
3. After 3 yrs Avogadro distinguished between atoms and molecules.
4. Modern atomic theory came into existence , with the discovery of X-rays by Rontgen in 1895, and
radioactivity by Becquerrel in 1896 followed by the discovery of electron in 1897 by J.J. Thomson .
Preceded by negative charges of electron.
5. After X-ray scattering experiments it was clear that atoms contain electrons, as well as positive
charges.
4. 6. In 1896 Becquerel detected by chance faint traces of the existence of the nucleus in
the atom. Followed by the Curies discovery of radioactivity. To be followed by the
scattering of α particles by Au .
7. Then in 1930s there were discoveries that culminated in the climax of demonstrations
near the end of the 2nd world war of the tremendous energy locked up by the force that
holds the atomic nucleus together. Then in 1932 Chadwick discovered neutrons. So that
is how more or less we have some idea of the constituents of the atom.
5. Applications of nuclear Physics
1.Generation of nuclear energy .
2. Radiation therapy
3. Preservation of food
4. Nuclear medicine and diagnostics .
5. Thermonuclear fusion.
6. Applications in archaeology and history.
7. Study of medicinal herbal plants.
8. Study of rock samples as well as artefacts .
9. Uses of rare earth materials in making solar cells .
10. Cosmic studies .
6. Units
When we travel from
Shillong to Gauhati what
units do we use to
express the distance ?
• Similarly to express the size of an
atom
• What units do we use ?
• Finally we concentrate on the
nucleus and talk in terms of Fermi,
• (fm)
• If we want to express cross section
then its barns or mb .
When we travel from
Shillong to Gauhati what
units do we use to express
the distance ?
When we measure the length
Of a room what units do we
use ?
When we measure the length
Of an ant what units do we
use ?
7. What is the advantage of using such units .
Let me give a practical example
Calculate the Coulomb potential
School Level
r
q
q
Vc
2
1
9. Home work
Calculate ) for different values of r and plot a graph .
Vc(r
Salient features
10. Salient Features of Rutherford s classical scattering of alpha particles
When the impact parameter b R, e.g b1 the α particle will not be deflected much.
When b > R , e.g b 2 , the α particle will be slightly deflected .
When b R e.g b3 the α particle will be deflected very much. Since repulsion is maximum.
When b R the Coulomb repulsion also becomes maximum.
When the α particle approaches the Au nucleus it is slowed down by the Coulomb repulsion.
Then it is speeded up on its way out.
13. As we probe the atom with increasing magnification , smaller and
smaller structures become visible: the nucleus, the nucleons, and finally
the quarks.
.
10
10 m
Atom
Nucleus
0
3.0
Na Atom
eV
Pb nucleus
208
3.0
MeV
14
10
m
Protons &
neutrons
14. Conventional Units to be used in nuclear Physics
1fm=10-15m
1barn=10-28m2
1barn= 10-28 m2 = 100fm2
ћc=197.3MeVfm
Mn = 939.57MeV/c2 E=Δmc2
Mp = 938.28MeV/c2 Me =0.5MeV/c2
1 amu=931.5MeV/c2
s
fm
c /
10
3 23
MeVfm
e
44
.
1
4 0
2
137
1
4
2
c
e
15. Show that the W.L of a photon of energy 1MeV is 1240fm
