12/24/2023 0 Comments Clipping detector projectThe term m 0c 2 is the rest mass of the electron, equal to 511 keV. Where E is the incident gamma-ray energy and θ is the angle of scatter. The energy of the scattered photon E′ is: This process is called Compton scattering. The photon can scatter by a free electron and transfer an amount of energy that depends on the scattering angle. This produces a characteristic full-energy peak in the spectrum that can be used for the purpose of identifying the radioactive material. This is a useful process for spectroscopy since an output pulse in a detector is produced that is proportional to the gamma-ray energy, as all of the energy of the gamma ray is transferred to the detector. The electron is ejected with an energy equal to the initial photon energy minus the binding energy of the electron. In this process the photon interacts with an electron in the material losing all of its energy. The photoelectric effect is a common interaction between a low-energy gamma ray and a material. There are three dominant gamma-ray interactions with matter: A schematic is shown in Figure 1-2.įigure 1-2: lllustration of a scintillation event in a photomultiplier tube The NaI(Tl) crystal is protected from the moisture in the air by encasing it in aluminum, which also serves as a convenient mounting for the entire crystal/photomultiplier unit. This is taken from the anode of the photomultiplier, and is a negative pulse. The first pulse from the photocathode is very small and is amplified in 10 stages by a series of dynodes to get a large pulse. ![]() The detector crystal is mounted on a photomultiplier tube which converts the scintillation into an electrical pulse. ![]() The scintillation occurs when scintillator electrons, excited by the energy of the photon, return to their ground state. The thallium-activated sodium iodide detector, or NaI(Tl) detector, responds to the gamma ray by producing a small flash of light, or a scintillation. The term beta decay means β- (electron), β+ (positron) emission or electron capture by the nucleus.įigure 1-1: Energy level sequences for 137Cs, 60Co and 22Na (energy levels in MeV) The energy levels and decay process of 22Na, 60Co and 137Cs are given in Figure 1-1. The energy level sequence and therefore the gamma-ray energy spectrum for every nucleus is unique and can be used to identify the nucleus. Often the decay is to an excited state in the daughter nucleus, which usually decays by emission of a gamma ray. ![]() How gamma rays are produced Radioactive nuclei decay by emitting beta or alpha particles.
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