Scintillation detectors radiation detection methods

All methods of radiometric analysis involve, of course, the use. of various radiation detection devices, The devices available for measuring radioactivity will vary with the types of radiations emitted by the radioisotope and the kinds of radioactive material. Ionization chambers are used for gases Geiger-Miiller and proportional counters for solids liquid scintillation counters for liquids and solutions and solid crystal or semi-conductor detector scintillation counters for liquids and solids emitting high-energy radiations. Each device can be adopted to detect and measure radioactive material in another state, e.g., solids can be assayed in an ionization chamber. The radiations interact with the detector to produce a signal,... 

The principal methods for detecting and quantifying radioactivity on TLC plates are autoradiography, zonal analysis (plate scraping followed by liquid scintillation counting), and direct measurement using radiation detectors. The method employed for analysis depends on the available equipment, which generally depends on the amount of money available, and the type of experiment and information required. The various detection methods are discussed in outline below, and more detailed information can be obtained from the literature cited. 

Over the last 30 years or so the detection of radioactivity directly on TLC plates has taken dramatic leaps forward. Prior to the introduction of radiation detectors, the classical method used for the detection and quantitation of radioactivity on a plate involved exposure to x-ray film as the first step. This could take from a few hours up to one or two months, and this technique only located the radioactivity. The second step after location was quantitation, which was achieved by removing the zone of interest, either by scraping the silica gel off or by cutting away if the plates were aluminum- or plastic-backed, followed by liquid scintillation counting. Such a procedure is extremely labor intensive and is limited in terms of accuracy and resolution (see above). 

Most of the radioisotopes used as isotopic labels in activation analysis decay with beta (positron and negatron) radiations and/or gamma rays. By convention, beta-emitting radionuclides are usually measured by gas-filled or gas-flow proportional counters or Geiger counters. Sometimes, liquid scintillation counters are used to complete a beta-ray measurement. The more conventional method for gamma-ray measurements involves the use of a gamma-ray spectrometer equipped with either a scintillation or solid-state detector. Stevenson (918) discusses the characteristics of radioactive decay and gives details on the methods and instruments used to detect emitted radiations. 

The three main ways of detecting radioactive isotopes on TLC plates are (1) film registration or autoradiography, (2) zonal analysis (plate scraping and liquid scintillation counting), and (3) direct, in situ methods using radiation detectors. 

Effect of Radiation on Matter—The ionizing power of radiation (Fig. 25-10) is the basis both of radiation s effects on matter and methods used to detect radiation. Radiation detectors include simple film badges, Geiger-Miiller (G-M) counters for routine measurements (Fig. 25-11), and scintillation counters in biomedical studies. Two units of measure are used to quantify exposure to radioactivity. One—the rad (radiation absorbed dose)— is related to the amount of radiation energy absorbed, while the other—the rem (radiation equivalent for man)—takes into account the differing effects of the various types of radiation (Table 25.5). 

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