High-energy radioactivity

A schematic representation of a Geiger-Muller counter. The high-energy radioactive particle enters the window and ionizes argon atoms along its path. The resulting ions and electrons produce a momentary current pulse, which is amplified and counted. 

The next subject we will address is that of scintillators. These are phosphors used to detect a, p, and y rays from incident sources. This application has become very important with the advent of CT-scanners and the PET-scanner, i.e.- CT = "computerized tomagraphy" and PET = "positron emission tomography". In all cases, radioactive Isotopes are used as the source of these "rays", including positrons, i.e.- positive electrons, p. Although scintillation, i.e.- detection of high energy radioactive-decay particles, may occur for nearly all phosphors, efficient scintillators must satisfy the following requirements for practical use. 

In comparison with most other analytical techniques, radiochemical methods are usually more expensive and require more time to complete an analysis. Radiochemical methods also are subject to significant safety concerns due to the analyst s potential exposure to high-energy radiation and the need to safely dispose of radioactive waste. 

The camera actually images the annihilation events, not the radioactive decay events directiy. Thus imaging of high energy positron emitters can have a limiting resolution owing to the range of the positron. 

The selective uptake of iodide ion by the thyroid gland is the basis of radioiodine treatment in hyperthyroidism, mainly with although various other radioactive isotopes ate also used (40,41). With a half-life of eight days, the decay of this isotope produces high energy P-particles which cause selective destmction within a 2 mm sphere of their origin. The y-rays also emitted are not absorbed by the thyroid tissue and are employed for external scanning. 

All radioactive isotopes decay with a characteristic half-life. For example, Fe decays with a half-life of 45 days, while Cu decays with a half-life of 12.6 hours. As a result of the decay, signature high-energy photons or y rays are emitted from a given radioisotope. Thus, Fe emits two prominent y rays at 1099 and 1292 keV, " Na emits at 1368 and 2754 keV, and Zn emits at 1115 keV. Compilations of y rays used in NAA can be found in y-ray tables. 

A radioactive nucleus spontaneously decomposes ( decays ) with the evolution of energy. As pointed out in Chapter 2, a few such nuclei occur in nature, accounting for natural radioactivity. Many more can be made ( induced ) in the laboratory by bombarding stable nuclei with high-energy particles. 

The first radioactive isotopes to be made in the laboratory were prepared in 1934 by Irene Curie and her husband, Frederic Joliot They achieved this by bombarding certain stable isotopes with high-energy alpha particles. One reaction was... 

G. See Free energy Gadolinium oxide, 147 Gamma radiation High-energy photons emitted by radioactive nuclei, 30, 513-514,516,518f Gas... 

Nuclear activation analysis (NAA) is a method for qualitatively and quantitatively detg elemental compn by means of nuclear transmutations. The method involves the irradiation or bombardment of samples with nuclear particles or high-energy electromagnetic radiation for the specific purpose of creating radioactive isotopes from the stable or naturally-occurring elements present. From the numbers, types and quantities of radioactive elements or radionuclides, it is possible to deduce information about the elemental compn of the original sample... 

At the top of the atmosphere, more properly at altitudes where the density is sufficiently low, high-energy cosmic ray particles cause nuclear chemical reactions with important products. The production of radioactive (or radiocarbon) already has been mentioned. 

Radioactive Isotopes are chemically identical to their natural, nonradloactlve counterparts, but their high-energy decays allow them to be detected even though they may compose only a tiny fraction of the overall isotopic... 

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