Radionuclides, analysis evaporation

The sample may arrive unliltered or separated as filtered water and the filter that contains the solids. The water sample is preserved with dilute acid or a preservative suitable for a radionuclide such as 1 that may be lost from an acid solution. Water without suspended solids is ready for evaporation to measure the gross alpha- and beta-particle activity, measure gamma rays by spectral analysis, and perform radiochemical analysis. The solids usually are counted similarly and then processed for dissolution as described in Section 6.2.1 for subsequent radionuclide analysis. 

When a liquid volume of several liters is needed to achieve a specified sensitivity for radionuclide detection, the volume usually is reduced for ease of analysis. Evaporation is a simple approach. A faster process— and one that is necessary for samples of seawater or other high-salt-content solution—is precipitation of the radionuclides of interest from the large sample volume with a carrier in bulky insoluble forms such as phosphate, hydroxide, or carbonate. The precipitate bearing the radionuclides of interest is separated by decanting most of the solution and filtering the rest, and is then dissolved for further radionuclide purification. 

Evaporation is a method for preconcentration used in the analysis of water samples. The enrichment factor is between 10 and 10 This approach however may lead to losses of certain elements due to adsorption on the walls of the vessels. That is why evaporation nowadays is practically used in the preconcentrations of radionuclides from waters since the carriers prevent adsorption (Das et al., 1983 Mizuike, 1983 Toelgyessy and Kyrs, 1989). 

There are several potential sources of radioactive materials that can contaminate water (see Chapter 4, Section 4.14). Radioactive contamination of water is normally detected by measurements of gross P activity and gross a activity, a procedure that is simpler than detecting individual isotopes. The measurement is made from a sample formed by evaporating water to a very thin layer on a small pan, which is then inserted inside an internal proportional counter. This setup is necessary because P particles can penetrate only very thin detector windows, and a particles have essentially no penetrating power. More detailed information can be obtained for radionuclides that anit y-rays by the use of gamma spectrum analysis. This technique employs solid-state detectors to resolve rather closely spaced y peaks characteristic of specific isotopes in the sample s spectra. In conjunction with multichannel spectrometric data analysis, it is possible to determine a number of radionuclides in the same sample without chemical separation. This method requires minimal sample preparation. 

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