Radionuclides, analysis extraction

NAA is preferred for the analysis of unique samples such as meteorite, the certification of reference materials, and quality assurance in analytical chemistry [21]. Definitive methods are based on the activation of samples, selective separation of analyzed radionuclides by column (ion-exchange) chromatography, and measurement by gamma spectrometry [15, 16, 19]. In definitive methods, radiochemical separation, co-precipitation, extraction, and ionic exchange guarantee the... 

The main and unique advantage of this method is the fact that quantitative separation of the element or compound to be determined is not necessary. It is substituted by measuring any fraction. This advantage is most clearly illustrated by an example from biology if the blood volume of an animal is to be determined, it is obvious that the animal will not survive the extraction of the whole amount of blood to be measured. By application of isotope dilution analysis, a small measmed volume V of a solution is injected that contains a measured activity of a radionuclide of low radiotoxicity. Mixing is effected by blood circulation. After some minutes, a small volume of blood is taken and the activity is measured. In analogy to eq. (17.15), the unknown volume is... 

To separate and purify the radionuclide of interest in the sample, the analyst can depend on the similar behavior of the stable element and its radioisotopes. Chemical reactions involving the radionuclide will proceed with essentially the equilibrium and rate constants known for the stable element in the same chemical form. Slight differences result from small differences between the isotopic mass of the radionuclide and the atomic mass (i.e., the weighted average of the stable isotopic masses) of the stable element. Because of this similarity in chemical behavior, many ra-dioanalytical chemistry procedures were adapted from classical quantitative and qualitative analysis. For the same reason, new methods published for separating chemical substances by processes such as precipitation, ion-exchange, solvent extraction, or distillation are adapted for and applied to radionuclides. One exception occurs when the radionuclides to be separated are two or more isotopes of the same element. Here, effective separation can be accomplished by mass spectrometer (see Chapter 17). 

Fifteen trace elements were determined at ng/g mass fraction levels in high purity Sn by Kolotov et al. (1996) using extraction chromatography on Teflon-supported tributylphosphate (TBP). Tin, together with Sb and In radionuclides, which are formed in secondary nuclear reactions of Sn during irradiation, were retained from 6 M HCl on the column. The Na was removed from the eluted trace element fraction by sorption on hydrated antimony pentoxide (HAP). Gas phase impurities of N, C, and O were also analyzed in the same material by radiochemical photon activation analysis via N, C, and detection. 

It is also possible to make measurements in situ, for example portable gamma detection equipment can be used if the target radionuclides can be characterised by key-line gamma energy levels. Considerations of the specimen size leads to an important difference between in situ investigations of chemically contaminated land and radioactively contaminated land. It is possible to make field measurements in situ of the chemical concentration of metals in soil by using Portable X-Ray Fluorescence (PXRF) equipment. In PXRF, the specimen size is of the order of a few cubic millimetres. It is therefore much smaller than a typical specimen that would be extracted for laboratory analysis. ... 

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