Radioisotopic sources, common

Common radioisotope sources of alpha particles are listed in Table 5.6. All but the first one listed are members of radioactive decay chains. Decay chains are classified into four groups according to their mass numbers. They are Th-series whose mass number is 4N (N is integer), U-series of 4N+2, Ac-series of 4N+3 and Np-series of 4N-fl. An Np-series does not exist naturally because the half-life of its longest-lived member is... 

The resulting manganese Ka line at about 2.1 A has proved to be a useful source for both fluorescence and absorption methods. Table 12-2 lists some additional common radioisotopic sources for X-ray spectroscopy. 

X-rays of discrete energy are also generated as a result of various types of radioactive decay processes. In such processes harder radiation (y-rays) is usually produced as well. Table 1 gives an overview of radioisotopes most commonly used as sources of X-rays, together with some of their characteristics. 

Radioisotope sources can be used in place of x-ray tubes. Radioisotope equipment has inherent hazards, and great care must be taken with its use. Only fully trained and licensed personnel should work with this equipment. As with x-rays, the most common method of measuring gamma ray transmission is with film. 

Radioisotopes have become very important ia the practice of modem medicine, for both diagnosis and treatment. Some diagnoses are done by injecting a radionucHde ia a biochemical form such that it goes to a particular organ, and the measured radiation then allows the functional level of that organ to be determined. A common treatment is to expose a portion of the body, for example a tumor, to radiation from a radioisotope with the source either internal or external to the body. Another usage iavolves radioactively labeled antibodies (see Immunoassay). 

The basic unit of radioactivity is the curie, Ci. One curie is the amount of radioactive material that emits particles at a rate of 3.7 X 1010 disintegrations per second (dps), or 2.2 X 1012 min-1 (dpm). Amounts that large are seldom used in experimentation, so subdivisions are convenient. The milli-curie (mCi, 2.2 X 109 min-1) and microcurie (yu,Ci, 2.2 X 106 min-1) are standard units for radioactive measurements (see Table 6.2). The radioactivity unit of the meter-kilogram-seconds (MKS) system is the becquerel (Bq). A becquerel, named in honor of Antoine Becquerel, who studied uranium radiation, represents one disintegration per second. The two systems of measurement are related by the definition 1 curie = 3.70 X 1010 becquerels. Since the becquerel is such a small unit, radioactive units are sometimes reported in MBq (mega, 106) or TBq (tera, 1012). Both unit systems are in common use today, and radioisotopes received through commercial sources are labeled in curies and bequerels. 

The plant itself is a source of secondary solid waste membranes, and spent filter cartridges and related small parts have to be processed by common methods such as compaction or incineration to reduce their volume or have to be left for decay, if adsorbed radioisotopes have short half-Ufe time. 

The synthesis of fatty acids and sterols in the liver cytosol depends upon a common pool of acetyl-CoA. This was demonstrated by Decker and Barth in a series of experiments utilizing perfused rat liver [10]. Lipid synthesis was measured by incorporation of tritium from [ H]H20. They used (- )-hydroxycitrate to inhibit ATP-dependent citrate lyase and measured radioisotope incorporation into fatty acids and sterols as a function of the concentration of this inhibitor. A parallel decrease in incorporation into these two products was found as the concentration of (- )-hydroxycitrate in the perfusate was increased. Contrastingly, if radioisotopic acetate was used as the substrate in the perfusing medium, this inhibitor had relatively little effect on the rate of sterologenesis, a result that would be expected if the natural source of acetate was from the action of the cytoplasmic citrate lyase. Their experiments also demonstrated that the ratio of fatty acid synthesis to sterol synthesis in the liver of fed rats is about 10 1. 

Experimental explosions of nuclear bombs are direct as well as indirect sources of numerous radioisotopes corresponding to many elements. During the fission of U with thermal neutrons, about 60 radioisotopes are produced primarily and this number is increased stepwise by radioactive decays to 180 radioisotopes of 35 elements with proton numbers of 30 to 65 and nucleon numbers of 72 to 161. Further radioisotopes are produced indirectly, i.e. by the activation of structural materials of the bomb, and of the the dust and common components of the atmosphere. The intensity of a nuclear explosion has no essential effect on the qualitative problem of the radioactive aerosols formed, however, it contributes significantly to their distribution in the atmosphere. The heat energy released in the explosion of smaller bombs (up to tens kt TNT) is rapidly dispersed and the convec- tive air motion driving radioactive particles is usually arrested prior to a possible transport of the fission products beyond the tropopause. Explo-... 

The sealed-source techniques are the most common radioisotope... 

Radioisotopes commonly used for energy-dispersion analysis are listed in Table 14.3. Sealed sources of all types are now commercially available. The price of a source depends on the cost of the radioisotope and the complexity of the instrument design. 

X-radiation is a product of radioactive decay of certain isotopes. The term gamma ray is often used for an X-ray resulting from such a decay process. Alpha and beta decay and electron capture processes can result in the release of gamma rays. Table 8.4 lists some common radioisotopes used as XRF sources. 

Table 3.6 summarizes the characteristics of some of the commonly used radioisotopes. Fe is useful for exciting the light-element K lines from sodium to titanium. The silver K lines from the Cd source are efficient for exciting the medium-atomic-number element K lines from about chromium to niobium. The 88.2-keV y-ray from Cd is extremely effective for exciting the K lines from heavy elements such as platinum, gold, mercury, and lead. With the nep-... 

Bie most common supply of carrier-free lead radioisotopes has been natural radium or thorium samples, Due to the presence of appreciable amounts of stable lead In pitch-blend which Is the principle source of radium or In thorium ores It Is necessary to obtain the carrier-free material from a sample which has previously been purified from lead. A convenient separation Is that of diffusion of the noble gas member of the radium or thorium decay chain from the parent material and its subsequent decay to radioactive lead Isotopes. Very early In the studies of radioactivity It was found that very high specific RaD(Pb ) sources could be obtained by... 

At the beginning of the 20th century, radium was used to estabhsh the standard prototype of the curie. Actually, one curie is exactly equal to the radioactivity of a source that has the same radioactivity as 1 g of the radionuchde radium-226 in secular equilibrium with its derivative, radon-222 (or emanation). In spite of the new mandatory SI unit of radioactivity, the bec-querel, symbol Bq, the curie, Ci, is sometimes still in use (1 Ci = 37 GBq). Twenty-five isotopes are now known radium-226, the most common isotope, has a half-life of 1620 years. This isotope is purged from radium and sealed in minute tubes, which are used in the treatment of cancer and other diseases. Radium is used in the production of self-luminous paints, neutron sources, and in medicine for the treatment of disease. Some of the more recently discovered radioisotopes, such as Co or Cs, are now being used in place of radium. Some of these sources are much more powerful, and others are safer to use. Inhalation, injection, or body exposure to radium can cause cancer and other bodily disorders. The maximum permissible burden in the total body for Ra is 7.4 kBq. 

Equation (7.37) can be solved for certain boundary conditions that can be approximated experimentally. For example, a common technique to measure D is to deposit a very thin film of a radioactive isotope (or mass isotope) on a plane surface of a thick sample and, after annealing for fixed times, determine the concentration of the diffusing species as a function of distance. Our experimental system approximates to the case of diffusion of a thin planar source in a semiinfinite solid. If the initial thickness of the layer of radioisotope is small compared to the distance over which the radioisotope diffuses, the solution of Eq. (7.37) is... 

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