METHODS FOR PREPARING COMPARATIVE STANDARDS AND FIELD SAMPLES FOR NEUTRON-ACTIVATION ANALYSIS OF SOIL

One of the more difficult problems associated with comparative neutron activation analysis (CNAA) is the preparation of standards which are tailor-made to the desired irradiation and counting conditions. Freque ntly, there simply is not a suitable standard available commercially, or the resulting gamma spectrum is convoluted with interferences. In a recent soil analysis project, the need arose for standards which cont ained about 35 elements. In response, a computer spreadsheet was devel oped to calculate the appropriate amount of each element so that the r esulting gamma spectrum is relatively free of interferences. Incorpora ted in the program are options for calculating all of the irradiation and counting parameters including activity produced, necessary flux/bo mbardment time, counting time, and appropriate source-to-detector dist ance. The result is multi-element standards for CNAA which have optima l concentrations. The program retains ease of use without sacrificing capability. In addition to optimized standard production, a novel soil homogenization technique was developed which is a low cost, highly ef ficient alternative to commercially available homogenization systems. Comparative neutron activation analysis for large scale projects has b een made easier through these advancements. This paper contains detail s of the design and function of the NAA spreadsheet and innovative sam ple handling techniques.