Radioactive decay detection devices

Tritium is readily detectable because of its radioactivity. Under certain conditions concentrations as low as 370 )-lBq/mL (10 //Ci/mL) can be detected. Most detection devices and many analytical techniques exploit the ioni2ing effect of the tritium P-decay as a principle of operation (62,63). 

The changing of radioactive elements into other elements through radioactive emissions is called either radioactive decay or radioactive disintegration. By using radioactive rays, it is possible to detect whether a substance is radioactive or not. There are several methods to detect the types of radiations and their intensities. The most commonly used device to check the intensity of radioactivity is the Geiger-Mtiller counter. 

The curie, abbreviated Ci, is a standard unit of radioactive decay. It was originally defined as the rate at which 1 g of radium decays. Because of the relatively long half-life of Ra, the isotope served as a convenient standard. The curie is now defined as the quantity of any radioactive substance in which the decay rate is 3.700 X 10 disintegrations per second (2.22 X 10 DPM). Because the efficiency of most radiation detection devices is less than 100%, a given number of curies almost always yields a lower than theoretical count rate. Hence, there is the distinction between DPM and CPM. For example, a sample containing 1 /rCi of radioactive material has a decay rate of 2.22 x lO DPM. If only 30% of the disintegrations are detected, the observed count rate is 6.66 X 10 CPM. 

Radiocarbon and tritium can be used to determine the approximate age of water masses. Three age—depth zones were deduced from the distribution of tritium and C in the groundwater. As shown in Fig. 19 B, there is an upper zone containing tritium that extends from the water table down to a depth of 6—21 m. The levels of tritium indicate that the source is probably fallout from atmospheric nuclear-fission bomb tests. Inasmuch as the testing of fission devices began in 1954, the age of water in this depth zone is probably less than 25 yr. An intermediate zone in which tritium is absent but radiocarbon is detected extends to a depth of 75m below the upper zone. If the possibility of loss of by mechanisms other than radioactive decay is neglected, a residence time of 10 —10 yr. is indicated. The deepest zone contains no detectable radiocarbon. It is in this zone that the regional groundwater flows system moves to the northeast, as previously indicated on section A—A. ... 

Suppose you had a detection device that could count every decay event from a radioactive sample of plutonium-239 ti/2 is 24,000 yr). How many counts per second would you obtain from a sample containing 0.385 g of plutonium-239 ... 

Helium-leak detectors, radioactive decay detectors, and interferometer (optical) leak detectors are all capable of fine leak detection. The most commonly used in the biomedical device industry is the helium-leak detector. 

A number of artificial radionuclides are produced as a result of activation during nuclear weapons tests, operation of reprocessing plants and reactors in nuclear power stations, and in nuclear studies. Modem radioanalytical techniques have enabled activation products such as Na, Cr, " Mn, Fe, °Co, Ni Zn, °Ag, and " Sb to be detected in the environment [28,29]. Stainless steel containing iron, nickel, and cobalt is an important material in nuclear power reactors and is used to constmct nuclear test devices or their supporting stmctures [30,31]. During neutron activation of the stable isotopes of cobalt, radioactive isotope °Co (J = 5.27 years) is produced. It is a beta emitter and decays into °Ni, with energy niax of... 

Normally, a sample of argon gas does not conduct a current when an electrical potential is applied. However, the formation of ions and electrons produced by the passage of the high-energy particle allows a momentary current to flow. Electronic devices detect this current flow, so the number of these events can be counted. Thus the decay rate of the radioactive sample can be determined. 

A scintillation counter is another instrument often employed to detect radioactivity. This device uses a substance, such as sodium iodide, that gives off light when it is struck by a high-energy particle. A detector senses the flashes of light and counts the decay events. 

The last three chapters consider special aspects of radioanalytical chemistry that have become increasingly important and visible. Chapter 15 describes the automated systems that are used to measure radionuclides in the counting room and in the environment. Chapter 16 is devoted to identification and measurement of the radionuclides beyond the actinides. These are research projects at the cutting edge of radiochemistry that apply novel rapid separations in order to measure a few radioactive atoms before they decay. Much must be inferred from limited observations. In Chapter 17, several versions of mass spectrometers combined with sample preparation devices are described. The mass spectrometer, applied in the past as a research tool to detect a small number of radioactive atoms per sample, is now so improved that it serves as a reliable alternative to radiation detection for radionuclides with half-lives as short as a few thousand years. 

Certain interactions with matter of the radiation accompanying the decay of unstable nuclides (a- and /9-particles, y rays) are the basis for the detection and measurement of radioactivity These include photochemical processes, by which a radioactive sample placed in close contact with photographic emulsion causes blackening of the latter upon development (autoradiography) gas ionisation and the deriving production of current pulses that can be analysed and measured by suitable devices excitation of orbital electrons of special molecules, either in a crystalline form or in solution, with subsequent emission of light pulses to be converted into electric current by a photoelectric detector (scintillation)... 

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