Radioisotopes radiation emission from

The impact of radioisotopes on human health is caused by radiation emission from both the initial decay and any subsequent decay of daughter products. Although a number of radionuclides have been employed in industrial and defense applica-lions (see above section), only a limited number, a dozen or so, make it into soils... 

Most areas of research and appHcations involving the use of radioisotopes require a knowledge of what radiations come from each isotope. The particular apphcation determines what type of information is needed. If the quantity of a radionuchde in a particular sample or at a particular location is to be deterrnined and this value is to be deterrnined from the y-ray spectmm, the half-life of the nucHde and the energies and intensities or emission probabiUties of the y-rays of interest must be known. Usually it is preferable to use the y-rays for an assay measurement because the d- and P-rays ate much more readily absorbed by the source material, and may not reach the sample surface having their original energies. Once these energies are altered they caimot be used to identify the parent radionuchde. 

Some nuclei are unstable and emit particles and electromagnetic radiation. These emissions from the nucleus are known as radioactivity the unstable isotopes are known as radioisotopes and the nuclear reactions that spontaneously alter them are known as radioactive decay. Particles commonly involved in nuclear reactions are listed in the following table ... 

Positron emission tomography (PET) is an important diagnostic technique using radiation (Fig.19.8). It employs radioisotopes such as (half-life 20.3 min) or (half-life 124 s) that emit positrons when they decay. These are incorporated (quickly, because of their short half-lives) into substances such as glucose, which are injected into the patient. By following the pattern of positron emission from the body, researchers can study blood flow and glucose metabolism in healthy and diseased individuals. Computer-reconstructed pictures of positron emissions from the brain are particularly useful, because the locations of glucose metabolism appear to differ between healthy persons and patients with ailments such as manic depression (bipolar disorder) and schizophrenia. 

Ionizing radiation is an effective killer of microorganisms and cancerous tissues. Accordingly, it is used to sterilize medical devices, to irradiate food, and to treat tumors. Ionizing radiation includes emissions from radioisotopes and x-rays. X-rays have numerous beneficial uses and are tolerated well by humans in small doses. It is well known that exposure to excessive quantities of ionizing radiation can induce mutations and carcinogenesis and, in extreme cases, cause death. 

The decay of radioisotopes iavolves both the decay modes of the nucleus and the associated radiations that are emitted from the nucleus. In addition, the resulting excitation of the atomic electrons, the deexcitation of the atom, and the radiations associated with these processes all play a role. Some of the atomic processes, such as the emission of K x-rays, are inherently independent of the nuclear processes that cause them. There are others, such as internal conversion, where the nuclear and atomic processes are closely related. 

The half-hves, y-ray energies, and y-ray emission probabiUties given ia Table 15 are what is needed if the amount of a radioisotope present ia a sample is to be measured. However, there are other uses of radionucHdes where additional data concerning the decay are needed. If a radionucHde is to be iajected or implanted in vivo it is necessary to have data on all of the radiations produced to be able to assess the impact on the ceU stmcture. Table 16 gives samples of the data that can be useful ia this latter case. Such information can be obtained from some of the references above. There are also computer codes that can use the decay data from the ENSDF database to produce this type of information for any radionucHde, eg, RAD LIST (21). 

Radioactive isotopes that decay by the emission of alpha or beta radiation undergo a change in the nature of their nuclei and are converted into isotopes of other elements. The emission of gamma rays, on the other hand, does not change the nature of the nuclei of the radioisotopes from which the rays are emitted. Gamma rays are a form of dissipation of nuclear energy. 

Some radioisotopes decay emitting only gamma rays, but many do so by the concurrent emission of beta and gamma radiation. The rate at which radiation is emitted from the nuclei of different radioisotopes varies considerably. Each radioisotope has a unique form of decay that is characterized by its half-life (tV2), the time it takes for the radioactivity of the radioisotope to decrease by one-half of its original value (see Textbox 14). 

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... 

One of the most common forms of cancer in males is prostate cancer. In addition to surgery and chemotherapy, one treatment option is to place 40 or more titanium capsules, or seeds, in the malignant area. Each seed, which is the size of a grain of rice, contains radioactive iodine-125, palladium-103, or cesium-131, which decays by gamma emission. The radiation from the seeds destroys the cancer by interfering with the reproduction of cancer cells with minimal damage to adjacent normal tissues. Ninety percent (90%) of the radioisotopes decay within a few months because they have short half-hves. 

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