This presentation is by Hemn A.Rahman in physics department college of science salahaddin university year 2011.

1. Study of Gamma-ray Spectrum by
using Scintillation detector and
Single channel Analyzer

2. Radioactive decays
Radioactive decay is the spontaneous breakdown of an
atomic nucleus resulting in the release of energy and
matter from the nucleus. We know that a radioisotope has
unstable nuclei that does not have enough binding energy
to hold the nucleus together. radioisotope would like to be
stable isotopes so they are try to be stabilize. In the
process, they will release energy and matter from their
nucleus and often transform into a new element. This
process, called transmutation, is the change of one
element into another as a result of changes within the
nucleus. The radioactive decay and transmutation process
will continue until a new element is formed that has a
stable nucleus and is not radioactive.

3. Types of Decay
 Alpha Decay
 Beta Decay
- +1
+ -1
 Electron Capture.
 Gamma Decay
Gamma decay occurs because the nucleus is at too high
energy state. The nucleus falls down to a lower energy
state and, in the process, emits a high energy photon
known as a gamma particle. Flash Flash 1

4. What is gamma ray?
Gamma radiation is one of the three types of natural
radioactivity. Gamma rays are electromagnetic radiation.
Gamma rays are the most energetic form of electromagnetic
radiation, with a very short wavelength between 0.003 nm -
0.03 nm.
They are produced by sub-atomic particle interactions such
as electron-positron annihilation, radioactive decay.

5. Radioactive source (Na-22)
Sodium-22 is the radioactive source which has 11 protons
And 11 neutrons and by beta plus it is decay to Neon-22.
In general of stable nuclei

6. Decay scheme in general

7. Na-22 Decay scheme
Sodium 11
/10%
3.7 ps 90%
Neon
22Na 22Ne + γ + β+ + υe

8. Interaction of gamma radiation with matter
 Photoelectric effect
When a gamma-ray collides with an orbital electron of an atom
of the material through which it is passing it can transfer all its
energy to the electron and cease to exist. On the basis of the
Principle of Conservation of Energy we can deduce that the
electron will leave the atom with a kinetic energy equal to the
energy of the gamma-ray, This electron is called a
photoelectron.

9.  Compton effect
gamma-ray transfers only part of its energy to a valance electron
which is essentially free. Notice that the electron leaves the atom and
the gamma-ray deflects off in a different direction to that with which
it approached the atom. This deflected or scattered gamma-ray can
undergo further Compton Effects within the material. this effect is
sometimes called Compton Scattering.

10.  Pair production
The incident Gamma Ray photon will interact with mater
through pair production if its energy is greater than 1.02
Mev , in this process positron and electron will produced
then the positron annihilate the two photons of 0.511
Mev produced of opposite direction.

11. Scintillation detector
Is a detector which consist of a material which produce a
flashes of light when absorb a radiation. These materials are
variously called fluorescent materials, Scintillator .(we use
Thallium activated sodium iodide)Nai(TL).
Properties of Scintillators
 High scintillation efficiency.
 The conversion of radiation into light should be linear over a
wide range of energies.
 The medium should be transparent to the scintillation light.
 The decay time of the produced scintillation light should be
short.
 The index of refraction of the scintillator should be suitable.

12. Parts of scintillation detector
Anode
PMT
Scintillator Multi-channel
analyzer
Nai(Tl)
Radioactive
Amplifier
source
Dynodes
Photocathode

13. Nai(Tl) spectrum for Na-22
Electron positron annihilation
peak at 0.511 Mev
X-ray
Compton
edge
Photopeak 1275 Kev

14. Thanks for Attention
Prepared by
Fourth stage –physics Department -2010-2011