Applications of neutron activation analysis in determination of natural and man-made radionuclides

Neutron activation analysis (NAA), being essentially an isotopic and not an elemental method of analysis, is capable of determining a number of important radionuclides of radioecological interest with good precision and accuracy, by transformation into another, more easily quantifiable radionuclide. The nuclear characteristics which favour this technique may be summarized in an advantage factor relative to radiometric analysis of the original radioanalyte. Well known or hardly known examples include 235U, 238U, 232Th, 230Th, 129I, 99Tc, 237Np and 231Pa; a number of these are discussed and illustrated in analysis of real samples of environmental and biological origin. The advantages and drawbacks of this technique relative to conventional radiometric analysis and newer, mass spectrometric methods is also discussed. The value of NAA as an independent method in certification of radionuclide reference materials (where much remains to be done) is stressed. Where direct sample analysis is possible, NAA retains the important advantage of being essentially blank-free. Where pre-separation of the analyte is necessary, some suggestions for improving the reliability of pre-separation yields using internal, activable tracers are proposed. The use of NAA to allow 238U and 232Th to be used as endogenous (internal) radiotracers in alpha spectrometric analyses of uranium and thorium radioisotopes in radioecological studies is described, also allowing independent data sets to be obtained, of great value in quality control. (author)