Study of Gamma-ray Spectrum by using Scintillation detector and Single channel Analyzer
Radioactive decaysRadioactive decay is the spontaneous breakdown of anatomic nucleus resulting in the release of energy andmatter from the nucleus. We know that a radioisotope hasunstable nuclei that does not have enough binding energyto hold the nucleus together. radioisotope would like to bestable isotopes so they are try to be stabilize. In theprocess, they will release energy and matter from theirnucleus and often transform into a new element. Thisprocess, called transmutation, is the change of oneelement into another as a result of changes within thenucleus. The radioactive decay and transmutation processwill continue until a new element is formed that has astable nucleus and is not radioactive.
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
What is gamma ray?Gamma radiation is one of the three types of naturalradioactivity. Gamma rays are electromagnetic radiation.Gamma rays are the most energetic form of electromagneticradiation, with a very short wavelength between 0.003 nm -0.03 nm. They are produced by sub-atomic particle interactions suchas electron-positron annihilation, radioactive decay.
Radioactive source (Na-22)Sodium-22 is the radioactive source which has 11 protonsAnd 11 neutrons and by beta plus it is decay to Neon-22.In general of stable nuclei
Interaction of gamma radiation with matter Photoelectric effectWhen 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.
Compton effectgamma-ray transfers only part of its energy to a valance electronwhich is essentially free. Notice that the electron leaves the atom andthe gamma-ray deflects off in a different direction to that with whichit approached the atom. This deflected or scattered gamma-ray canundergo further Compton Effects within the material. this effect issometimes called Compton Scattering.
Pair productionThe 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.
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.
Parts of scintillation detector Anode PMT Scintillator Multi-channel analyzer Nai(Tl)Radioactive Amplifiersource Dynodes Photocathode
Nai(Tl) spectrum for Na-22 Electron positron annihilation peak at 0.511 Mev X-ray Compton edge Photopeak 1275 Kev
Thanks for AttentionPrepared by Fourth stage –physics Department -2010-2011