Performance optimization of systems containing Boron-10 lined proportional counters

Previous studies have reported the results of optimization of coating thickness for individual Boron-lO (B-lO) lined proportional counters and radiation portal monitor neutron detection modules (NDM) containing multiple B-IO lined proportional counters in order to maximize neutron detection efficiency. In this work, we report on the extension of these investigations into the optimization of systems used in international safeguards applications such as passive and active well counters, where the figure of merit (FOM) to be maximized is not simply neutron detection efficiency, but the ratio of efficiency squared to die-away time. These two parameters are not independent, and in many cases steps taken to improve one results in a degradation of the other. The optimal value for the figure of merit of a full system, therefore, may be obtained by a design that is not optimal in either efficiency or die-away time. In this study, the impact of B-lO coating thickness, detector diameter, and moderator design on system efficiency and die-away time are studied. Optimal conditions are reported for NDM systems where detection efficiency must be maximized and international safeguards well counters where the efficiency and die-away time must be optimized to maximize the figure of merit. In all cases, optimization is attempted with the fewest detectors possible in order to reduce overall system cost and improve reliability.