Maintaining measurement accuracy in prompt gamma neutron activation analyzers with variable material flow rates or material bed depth

摘要

A method of maintaining measurement accuracy of specific constituents in prompt gamma neutron activation analyzers in a flow of bulk material having a known range of flow rates comprising of the steps of providing a plurality of samples of the bulk material in the form of standard geometric units, each said unit having the same concentration of the specific constituent to be measured and said units in a form that can be arranged to pass through the analyzer in the same manner as the bulk material; for insertion into the analyzer in geometries and quantities referred to as loading profiles that range from the smallest to the largest flow rates to be expected with the specific bulk material and the specific analyzer, successively inserting each of the loading profiles into the analyzer and measuring long enough to yield a measurement uncertainty that is small compared to the observed differences in analysis results from one loading to another, and recording these results and computing the differences of the measurements between loading profiles, hereafter referred as measured errors, in a table, and then removing the loaded profiles, mathematically fitting the measured errors for each constituent at each loading to one or more mathematical expressions that are derived from the loading values, so as to allow subsequent mathematical generation of the expected error at any loading value, utilizing the real-time flow rate of the unknown material to calculate expected errors for each constituent based upon the mathematical functions and parameters derived in said previous steps, and subtracting the estimated or predicted measurement errors determined in the prior step from the measured values to determine the corrected or true value.