These rays, which are so useful for internal examination of the human body, are produced by accelerating electrons in a vacuum chamber to energies in the kilovolt range and allowing them to strike a heavy element target, such as tungsten (see Section 13.8).įrancesco Collamati. When electrons of inner orbits in heavy elements are displaced, the resultant high-energy radiations are classed as X-rays. If its energy is large, it may impart energy to atomic electrons as described by the Bohr theory ( Section 2.3), causing excitation of electrons to higher energy states or producing ionization with subsequent emission of light. If an electron that enters a material has a very low energy, it will merely migrate without affecting the molecules significantly. ![]() The former two processes occur in the familiar fluorescent light bulb, in an X-ray machine, or in matter exposed to beta particles. When electrons pass through matter, several possible processes may occur, including ionization, excitation, and bremsstrahlung, as illustrated in Fig. Holbert, in Nuclear Energy (Eighth Edition), 2020 5.2 Light Charged Particle Interactionsįor our purposes, light charged particles are electrons (e −), positrons (e +), and beta (β) particles. ![]() ![]() In general, it is important to remember that when quantifying radionuclides by Cherenkov counting, the counting region should be set to a lower energy (0–50 keV) to encompass only the low pulse height spectra produced by Cherenkov photons, and no fluor cocktail is required. The process of Cherenkov counting is treated in detail in Chapter 9. The Cherenkov counting efficiency of these radionuclides is in the range of approximately 35–70% depending on color quench. Some examples are 32P ( E max = 1710 keV), 90Sr( 90Y) where the E max of 90Y beta particles is 2280 keV, 86Rb ( E max = 1770 keV occurring at an 88% intensity (probability per decay) or 680 keV at a 12% intensity) and 89Sr ( E max = 1490 keV). High-energy beta-particle emitters, which emit a significant number of beta particles in excess of 263 keV, can be analyzed by counting the Cherenkov photons in the liquid scintillation analyzer without fluor cocktail. The light that is produced is low intensity and is normally detected in the low-energy counting region of 0–50 keV. When this occurs, the charged particle will produce Cherenkov photons, which extend from the ultraviolet into the visible wavelengths. Charged particles, such as beta particles, that possess sufficient energy can travel at a velocity exceeding the speed of light in media such as water, organic solvents, plastic, and glass. ![]() The sample is simply placed in a clear liquid solution (often aqueous) and detected by the light produced by the Cherenkov effect. Cherenkov Photon Countingīeta particles of energy in excess of 263 keV can be detected and quantified in water or other liquid medium using the liquid scintillation analyzer without the use of scintillation fluor cocktail. KESSLER (DECEASED), in Handbook of Radioactivity Analysis (Second Edition), 2003 C.
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