Radioactive isotope identification

In essence, NAA involves converting some atoms of the elements within a sample into artificial radioactive isotopes by irradiation with neutrons. The radioactive isotopes so formed then decay to form stable isotopes at a rate which depends on their half-life. Measurement of the decay allows the identification of the nature and concentration of the original elements in the sample. If analysis is to be quantitative, a series of standard specimens which resemble the composition of the archaeological artifact as closely as possible are required. NAA differs from other spectroscopic methods considered in earlier chapters because it involves reorganization of the nucleus, and subsequent changes between energy levels within the nucleus, rather than between the electronic energy levels. 

Radioactive Taggants Addition of small amounts of radioactive isotopes to expls during the manufg process appears to be particularly attractive at first glance, as it provides a mechanism for both identification of the expl materials from the postdetonation debris, and a simple detection mechanism. There axe a large number of radioisotopes, so an identification scheme could certainly be developed that would provide sufficient unique code species, although there would be some limitations of availability and cost. 

The important developments in nuclear chemistry in which mass spectrometers have played a role will be reviewed in this chapter. These include the identification and determination of radioactive isotopes and of stable daughter products in nature, the accurate determination of half-lives for... 

It was clear from the time of the first fission product studies that the mass spectrometer would eventually be used in separation problems, mass identification, and isotope abundance measurements. However, the early work on fission products involved very small samples of material and only radiochemical methods were considered sensitive enough to identify and follow the radioactive isotopes. In 1945, Thode and Graham (104) succeeded in obtaining mass spectrograms of the xenon and krypton isotopes formed in the thermal neutron fission of U23B. 

Krypton, Kr, is an elemental, colorless, odorless, inert gas. It is noncombustible, nontoxic, and nonreactive however, it is an asphyxiant gas and will displace oxygen in the air. Krypton 85 is radioactive and has a half-life of 10.3 years. The four-digit UN identification number for krypton is 1056 as a compressed gas and 1970 as a cryogenic liquid. These forms of krypton are not radioactive. Radioactive isotopes of krypton are shipped under radioactive labels and placards as required. Its primary uses are in the activation of phosphors for self-luminous markers, detecting leaks, and in medicine to trace blood flow. 

The analytical application of radionuclides, along with other applications in radioanalysis, results directly from Hevesy and Paneth s invention of radio-tracer and radio-indication techniques in 1912. They pointed out that the addition to a solution of an element of its radioactive isotope makes possible the identification and determination of the element. In their first application they labeled a solution of lead with radium-D, a natural radioactive lead isotope and determined the solubility of sparingly soluble lead salts. 

Multiple labelling with both stable and radioactive isotopes offers the advantage of simultaneous labelling in the same position of a molecule [68]. The combination of C- and C-labelling combines ease of detection with rapid structural identification. The adoption of this technique in studies of some aspects of the metabolism of 4-morpholino-2-piperazinothieno [3,2-d] pyrimidine (V-K 774) (3) in the rat has been reported [69]. Potassium [ C, C]thiocyanate was prepared from a mixture of potassium [ C, C]cyanides. Reaction with ethyl bromide and methyl 3-aminothiophen-2-carboxylate (4) afforded the thienopyri-midine (5), which, by a series of reactions was converted to V-K 774 (3) labelled in the position shown. 

For illustrative purposes, Figure 1 shows the Gamma meter existing at ITN (Institute Tecnologico e Nuclear) where measurements of gamma radiation of phosphate rock were made as well as an identification of the radioactive isotopes by gamma spectrometry. 

In the case of the present study the radioactivity of the phosphate rock used for the production of agricultural fertilizer has been analyzed. This was carried out by measuring the radiation activity and identification of the radioactive isotopes in samples of phosphate rock used in the manufacture of fertilizers by gamma spectrometry performed in the ITN laboratory. The amount of radioactive isotopes present in phosphate rock samples from Tunisia, Syria, Morocco and Senegal was thus determined and the values shown in Table 1. 

A complementary approach consists in the identification and estimation of the elements present in a sample by partially convnting them to radioactive isotopes on exposure to a neutron beam. The induced radioactivity has a characteristic spectrum related both to the elemental constituents of the sample and to their individual concentrations (activation analysis). 

As with the bulk POM and DOM, the operationally defined fractions of UDOM and humic substances are quantified by elemental analysis and via broad molecular-class detection. Other strategies involve measurement of the natural isotopic composition, both stable and radioactive, of the various fractions. Efforts are underway to develop more sophisticated techniques, such as solid-state NMR and high-resolution mass spectrometry, far identification of specific bonds and functional groups. 

Since the alpha-ray impacts shattered only a minute proportion of the total number of atoms of boron, aluminum, or magnesium, the chemical identification of the products was extremely difficult. These indefatigable workers, however, accomplished even this. Although it would have been impossible to identify the products simply by ordinary chemical means, the Joliots were able to take advantage of the radioactive nature of the products formed. Since they had good reason to believe that the boron atom had captured a helion and ejected a neutron and that the new element was therefore probably an isotope of nitrogen, they heated some bombarded boron nitride with caustic soda and found that the liberated... 

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