Gamma y Radiation

A gamma ray has no charge and no mass. When a gamma ray is emitted from a radioactive atom, it does not change the mass number or the atomic number of the element. Gamma rays are usually emitted in conjunction with other types of radiation. For example, the alpha emission of U-238 (discussed previously) is also accompanied by the emission of a gamma ray. 

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The radioisotope cobalt-60, with a half-life of 5.27 years (1925.3 days) through beta ((3) emission, decays to form the stable element nickel-60. It is used to test welds and metal casts for flaws, to irradiate food crops to prolong freshness, as a portable source of ionizing gamma (Y) radiation, for radiation research, and for a medical source of radiation to treat cancers and other diseases. 

Scientists have known since 1896 that many nuclides are radioactive—that is, they spontaneously emit radiation. Early studies of radioactive nuclei, or radionuclides, by the New Zealand physicist Ernest Rutherford in 1897 showed that there are three common types of radiation with markedly different properties alpha (a), beta (f3), and gamma (y) radiation, named after the first three letters of the Greek alphabet. 

Radioactivity is the spontaneous emission of radiation from an unstable nucleus. Alpha (a) radiation consists of helium nuclei, small particles containing two protons and two neutrons (fHe). Beta (p) radiation consists of electrons ( e), and gamma (y) radiation consists of high-energy photons that have no mass. Positron emission is the conversion of a proton in the nucleus into a neutron plus an ejected positron, e or /3+, a particle that has the same mass as an electron but an opposite charge. Electron capture is the capture of an inner-shell electron by a proton in the nucleus. The process is accompanied by the emission of y rays and results in the conversion of a proton in the nucleus into a neutron. Every element in the periodic table has at least one radioactive isotope, or radioisotope. Radioactive decay is characterized kinetically by a first-order decay constant and by a half-life, h/2, the time required for the... 

The gamma (y) radiation exposure units used to express radiation doses are as follows ... 

IARC (2000). International Agency for Research on Cancer. Ionizing Radiation, Part 1 X- and Gamma (y)-Radiation, and Neutrons, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 75 (International Agency for Research on Cancer, Lyon, France). 

It was soon found that this new type of radiation was even more penetrating than X-rays. It was given the name gamma (y) radiation. It was also found that elements can emit other kinds of radiation as well. The other two most important are alpha (a) and beta O) radiation. 

The three most common kinds of radiation given off when a radionuclide decays are alpha (a), beta (j8), and gamma (y) radiation. (Section 2.2) A TABLE 21.1 summarizes some of the important properties of these types of radiation. As just described, alpha radiation consists of a stream of helium-4 nuclei known as alpha particles, which we denote as He or 2 . 

The RAMS is designed to monitor ambient gamma (y) radiation levels. The typical range for RAMS units is O.l mR/h to 10 R/h. Alarm set points are established at levels appropriate to the area being monitored, and to provide an indication of an abnormal condition. RAMS are located in Zone 2 where routine manned operations are conducted. RAMS units are calibrated and tested in compliance with the SNL RPPM Chapter 12. 

Further study of the nature of radioactivity, principally by the British scientist Ernest Rutherford (Figure 2.7 ), revealed three types of radiation alpha (a), beta (j8), and gamma (y) radiation. Each type differs in its response to an electric field, as shown in Figure 2.8 T. The paths of both a and j8 radiation are bent by the electric field, although in opposite directions, whereas y radiation is unaffected. 

The process can be regarded as a transition of a proton to a neutron. Also in this case a new element has been formed, one with a lower atomic number. The emitted positron is rapidly annihilated on coUision with an electron. Gamma (y) radiation is formed (see below). 

The study of radioactivity, beginning with Antoine-Henri Becquerel s discovery in 1896, was another problem relating to atomic structure. In fact, radioactivity was another enigma not explained by classical mechanics. Studies showed that atoms spontaneously gave off three distinct types of radiation, of which two were eventually shown to be particles of matter. The alpha particle (a) was identical to a doubly ionized helium atom, and the beta particle (/3) was identical to an electron. [The third type of radiation, gamma (y) radiation, is a form of electromagnetic radiation.] However, no known chemical process could eject particles from atoms in the manner indicated by radioactivity. 

Radioactive isotopes have unstable nuclei that break down (decay), spontaneously emitting alpha (a), beta (/3), positron (j3 ), and gamma (y) radiation. 

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