VALIDATION OF THE CUMULATIVE OR REPLICATE NAA METHOD FOR THE DETERMINATION OF TRACE-ELEMENTS IN BIOLOGICAL-MATERIALS

To make the best use of time and facilities, a neutron activation syst em, fully automatic, including spectrum and data processing, to be use d with short-lived nuclides, has been recently developed at the Portug uese Research Reactor (in Portuguese ''Reactor Portugues de Investigac ao,'' RPI). Using this system, the cumulative neutron activation analy sis method is now being implemented. This article summarizes the exper imental procedures used to validate the cumulative NAA method for the determination of selenium in biological samples, emphasizing the deter mination of the essential characteristics of precision, accuracy, and limits of detection and of quantification of the method. The article a lso examines how detection limits and precision are improved when the samples are analyzed by this method compared to the cyclic activation measurements in use at RPI for the determination of selenium. The impr ovement is demonstrated for the measurement of selenium in several ref erence materials when the result obtained by adding up seven spectra o f separate aliquots of the same sample is compared to the result from a cumulative spectrum of seven (whenever possible) consecutive cycles of a single sample.