Gamma decay is a type of radioactive decay in which an unstable nucleus emits gamma rays to reach a more stable state, often following other decay processes like alpha or beta decay. The document discusses various aspects of gamma decay, including the classification of gamma rays, selection rules for transitions, and the energetics involved in gamma decay processes. Additionally, it provides examples and diagrams related to specific isotopes and their decay pathways.

1. 1
Gamma decay
Radioactive decay

2. 2
Gamma decay Radioactive decay ……………….what is ?
Radioactive decay is a process in which an unstable nucleus spontaneously loses its
energy by emitting ionizing particles and/or radiation. This decay, or loss of energy,
results in a nucleus of one type, called the parent nucleus, transforming to a nucleus of
a different type, named the daughter nucleus .
Modes of decay
1- Alpha
2- Beta(EC, -
and +
)
3- Gamma
To get the stability a radioactive
nucleus decays via a particle like
alpha or beta and left parent
nucleus in excited state. This
excesses energy is emitted in the
form of gamma decay.

3. 3
Gamma Decay ……………… Level/decay diagram of general
Nucleus(Half life)
spin
Nucleus(life-time)
𝑺𝒑𝒊𝒏
Decay direction
of beta-article
Gamma
spin
Nucleus(Half life)
Decay direction
of beta-article

4. 4
Gamma Decay ……………… Level/decay diagram
Nucleus(Half life)
spin
Nucleus(life-time)
𝑺𝒑𝒊𝒏
Decay direction
of beta-article
Gamma
spin
Nucleus(Half life)
Decay direction
of beta-article
Excited
state
Ground
State

5. 5
Gamma Decay ……………… Level/decay diagram of 137
Cs
137
Cs(30.17 y)
0.6617 MeV
137
Ba(stable)
137
Ba(2.55 m)
0 MeV
𝟕
+¿
𝟐
¿
-
95 %
5 %
-

137
Cs is decaying into
137
Ba to get the stable
position by beta decay
95% of 137
Cs nuclei decay via -
particles to metastable state.
5% of 137
Cs nuclei decay via -
particles directly to ground state.

6. 6
Gamma Decay ….. Level/decay diagram of Radioactive Nucleus 137
Cs
137
Cs(30.17 y)
0.6617 MeV
137
Ba(stable)
137
Ba(2.55 m)
0 MeV
𝟕
+¿
𝟐
¿
-
95 %
5 %
-

What is gamma rays radiations
 -rays are the e. m. radiations
 Radiation produce as a result
of oscillations of electric
charge
 Current changing with time
producing gamma –rays
radiation

7. 7
-rays are the e. m. radiations can be classified in different categories!
Gamma Decay
We know charge has electric moment and magnetic moment
Electric moment
A charge distribution can be classified as
• Monopole moment
• Dipole moment
• Quadrupole moment
• And so on
Magnetic moment
A strength of magnet can be classified as
• Monopole moment
• Dipole moment
• Quadrupole moment
• And so on
If Monopole 0 : Out side the charge the field distribution is spherically in
symmetric and do not produce any radiations.
If monopole = 0
And Di-pole 0 Out side the charge, the field distribution is given by
If this charge oscillates will produce radiations and such kind of radiations are
called electric dipole radiations,
Similarly, for the higher order of electric and dipole moments,
)
1
cos
3
(
2
1
)
(cos 2
2 
 

P

8. 8
 These emitted gamma ray radiations carry some angular momentum
 If transitions is dipole L=1, quadrupole L=2 and octapole L=3 and so on
L is the angular momentum quantum number carried by the gamma rays, this
quantum number depends on type of transition
Gamma Decay
-rays are the e. m. radiations can be classified as
Electric moment (EL) Magnetic moment (ML)
• Electric Dipole moment(E1)
• Electric Quadrupole moment
(E2)
• Electric octapole moment(E3)
And so on
• Magnetic Dipole moment(M1)
• Magnetic Quadrupole moment (M2)
• Magnetic octapole moment(M3)
And so on
EL and ML called the Multi-polarity of the gamma rays

9. 9
Unit 3- Gamma Decay Selections Rule
Saturday, January 4, 2025 9
Gamma Decay ……………… Selection Rule , Multi-polarity
𝑱 𝒊❑

𝑱 𝒇 ❑

Initial State spin and parity 
Final state spin and parity 
Angular momentum of Photon L
Conservation of parity , must be
i
=f
Parity for electric type of transition is
given by the relation
f
=i
(-1)L
Parity for magnetic type of transition is
given by the relation
f
=i
(-1)L+1
Conservation of angular momentum
= +L
Hence L must be;

10. 10
Unit 3- Gamma Decay Selections Rule
Saturday, January 4, 2025 10
Gamma Decay
State the type of transition and multi-polarity in a given transition
2+
0+
Initial State spin and parity =2+
Final state spin and parity =0
+
Conservation of parity , must be
i
=f
Parity for electric type of transition is
given by the relation
f
=i
(-1)L
Parity for magnetic type of transition is
given by the relation
f
=i
(-1)L+1
Conservation of angular momentum
= +L
Hence L must be;
for L =2
EVEN
ODD
L =2
e.g.
Hence , transition is only eclectic type
E2 (Mulipolarity)

11. 11
Initial stage
Excited
state
Ground
state
Final stage
Nucleus
Recoil with
velocity
Momentum p
Mass m
E
E0, v=0 , m
Conservation of Energy:
(1)
Conservation of Momentum:
0
Or (2)
Form Eqn. (1) and (2)
(3)
It is very small
Hence,
E0
Gamma Decay Energetics of Gamma decay
How much energy can release in gamma
decay??
E0= Rest mass energy of the Nucleus
E=mc2
E=(A931.5) MeV/c2
E=A103
MeV/c2
The life time of the excited state can range
from 10-16
second to 100 years. Can
calculate using semi classical approch

12. 12
Gamma Decay …….Assignment
137
Cs(30.17 y)
136.907 amu
0.6617 MeV
137
Ba(stable)
136.905 amu
137
Ba(2.55 m)
0 MeV
-
95 %
5 %
-

137
Cs is decaying into
137
Ba to get the stable
position by beta decay
E1
E2
E3
Calculate E1-E3 , E1-E2 and E2-E3
Draw level diagrams for 60
Co and 22
Na
What is the difference between 80 keV X-ray and 80keV Gamma Ray

13. 13
1/2-
9/2+
Gamma Decay Assignment
State the type of transition and
multi-polarity in a given transition
Gamma ray energy of 137
Cs
To observation only

14. 14
γ-ray spectrum of 257
No
Quantum states in 257
No and 253
Fm
Energy spectrum observed through γ-ray
emitting transitions
To observation only
Gamma Decay

15. 15
Thanks