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GammaRaySpectroscopy

GammaRaySpectroscopy - GAMMA-RAY SPECTROSCOPY...

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1 GAMMA-RAY SPECTROSCOPY INTRODUCTION/THEORY This experiment will demonstrate that excited atomic nuclei occupy discrete and unique nuclear energy levels in much the same way that excited atoms exhibit discrete and unique atomic energy levels. When an atom undergoes a de-excitation transition, a photon is often emitted which carries off energy equal to the difference in energies of the two electronic levels involved. An analogous phenomenon occurs in nuclear transitions between nuclear energy levels. The photons emitted in nuclear transitions are called gamma-rays and generally have energies several orders of magnitude greater than atomic photons. In both the atomic and nuclear processes, the resulting photon spectrum is unique and provides a means of identifying either the chemical element or radioisotope present. The fact that the radiation pattern (spectrum) of each radioisotope is unique and the very high detection efficiencies of nuclear counting systems, facilitates many useful scientific applications of radioactive materials - medical diagnosis, biological and chemical tracers, neutron activation, etc. The gamma-ray spectrum will be obtained by using a Sodium Iodide (NaI) Scintillator Detector. The atoms of these type of detectors are easily excited by radiation and produce a spectrum that is characteristic of the chemical element present. A typical diagram of a NaI detector is shown below. Scintillator Crystal (NaI) 0 V Photocathode +150 V +300 V Photomultiplier Tube +450 V +600 V + 900 V +750 V Output Signal When a gamma-ray strikes the NaI crystal some of the atoms in the crystal will become excited and then emit photons as the atoms fall to their lower energy state. These photons will then
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