Basics of nuclear

physics

Contents: Structure of an atom

Rutherford’s atomic model

Bohr’s atomic model

Electrons and energy levels

Nuclear elements and nuclear stability

Radioactivity

Decay process

Interaction of radiation with matter

Structure of an atom

JJ Thomson’s plum pudding model

Rutherford’s planetary model

Rutherford’s experiment: scattering of

alpha particles.

Drawbacks:

According to Larmor theory electron

loses energy while orbiting nucleus.

Hence atom will collapse in 16

picoseconds

Bohr’s atomic model

According to Neil Bohr’s theory electron can have

only classical motions:

◦ Electrons in atoms orbit the nucleus.

◦ The electrons can only orbit stably, without

radiating, in certain orbits at a certain discrete set

of distances from the nucleus.

◦ Electrons can only gain and lose energy by

jumping from one allowed orbit to another,

absorbing or emitting electromagnetic radiation

with a frequency ν determined by the energy

difference of the levels according to the Planck

relation:

Electrons and energy levels

Mass of an electron: 9.1*10-28 g.

Charge: 1.59*10-19 coulombs.

A particle with same mass but a

positive charge is called positron.

No. of electrons in a shell is given by:

2n2 .

Binding energy of a single electron of

Hydrogen atom: Eb=-13.6/n2 eV

Nuclear elements

Fundamental constituents: neutrons

and protons.

Mass of proton: 1.672*10-24 g.

Neutron:

◦ No charge, mass ~ proton.

◦ Limited life in free state. Later

disintegrates into electron and proton.

Symbol:

Nuclear stability

Stability depends on n/p ratio.

Extra energy is released by the

nucleus by expelling particles or

photons.

Radioactivity

The process of transmutation of an

unstable element to another element

through the emission of radiation.

Unit: curie (Ci) (3.7*1010

disintegration/sec).

Radioactive decay law:

Half life of an element:

Decay Process

It consists of four processes:

Alpha decay

Beta decay

Positron decay

Gamma decay

Alpha decay

Alpha Decay Applications

?4

2

241

95

A

ZHeAm

Beta decay

AceRa 228

89

0

1

228

88

Positron Emission

ThePa 230

90

0

1

230

91

Gamma Decay

00240

94

240

94 PuPu

Decay Process

Isotopes: Z same, A different

e.g 1H1,1H

2, 1H3

Isobars: A same, Z different

e.g. 40S, 40Cl

Isotones: Same number of neutrons.

e.g. Cl-37, K-39

Isomeres: They are different excited

states of the same type of nucleus.

Electron capture:

Isomeric and Isobaric

Transition A nuclear process in which a nucleus

following the emission of an alpha

particle or a beta particle emits energy

without changing its number of protons

or neutrons.

Interaction of x-rays with

matter

Phoelectric effect:

Kinetic energy:EC= EO +EB

Compton Effect

The Compton effect (Compton scattering)

is the result of a high-energy photon

colliding with a target, which releases

loosely bound electrons from the outer

shell of the atom or molecule. The

scattered radiation experiences a

wavelength shift.

Pair Production Pair production is the creation of

an elementary particle and

its antiparticle, for example

an electron and the positron.

occurs when a photon interacts with a

nucleus.

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