Automation radionuclides analysis approaches

Both radiometric and mass spectrometric detection approaches have been used in automated radiochemical analysis, depending on the radionuclides of interest and the capabilities of the laboratory involved. The tradeoffs between radiation counting and atom counting have been described.14 16 17 Short-lived fission products may be advantageously detected with radiation detection, whereas long-lived (low specific activity) radionuclides can be determined with better sensitivity using ICP-MS. 

Many versions of this basic approach exist, the most significant variation being whether matrix inversion is used to connect a library of radionuclides to observed peak intensities or whether a list of energies of interest is used to make key calculations. Thus, the two main types today are matrix inversion and list directed. Automated spectral analysis software is available from commercial and academic sources with a mix of national and international quality certifications, specialized capabilities, and user control. Programs of this type can handle thousands of automated analyses per day and run on most types of computers. 

Most of the effluent and environmental radioactivity measurements are made using gamma-ray spectrometry. This is a far more cost effective approach than radiochemical analysis the Instrumental measurement can be readily automated, and detection decisions can be made more or less simultaneously for many radionuclides. The validity of those decisions, and of the corresponding detection limits, however, requires either that the peaks be Isolated and lie on a linear baseline, or that a detection limit model be employed which Is more complex than that used for "simple" counting. Baseline or interference model uncertainties should be Included, and an iterative solution is required to estimate the detection limit when spectrum deconvolution is involved. Details are beyond the scope of this chapter, but a relatively simple limiting estimate can be derived by treating the estimated standard error for a low level radionuclide peak of interest as though it were the null standard error, [12, p. 81]. 

Thus, the grade of automation reached will be limited principally by the level of activity found in the sample and the detector selected. The latter will mainly depend on the half-Ufe of the radionuclide of interest, in order to achieve the greatest sensitivity. Figure 8.1 shows different approaches used for the analysis of radionuclides, indicating the steps of the analytical protocol susceptible to be automated. 

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