Calibration of Fission Product Detection Systems by Means of Monte Carlo gamma Ray Transport

摘要

This report is the result of an initial investigation into the feasibility of calculating photopeak efficiency curves for any gamma-ray detection system using the photon-transport capabilities of the INEL RAFFLE Monte Carlo code. It is anticipated that substantial savings in time and money can be realized by using RAFFLE to generate the system photopeak efficiency curve. Additionally, a RAFFLE prediction of a detector-collimator-source efficiency curve might provide important data for the design of collimator/detector systems. The investigative approach consisted of using a modified RAFFLE code to predict the photopeak efficiency curves for two geometries for which experimental curves had been measured. The two geometries included the simple case of a point source emitter located on the detector axis 15.3 cm from the detector end cap, and the more complicated case of a collimated system. The test case for the collimated system was the PBF Fission Product Detection System (FPDS) installation viewing the gas effluent line. Each of these measured curves have an estimated overall error of +-20% from 60 to 250 keV, +-10% from 250 to 1500 keV, and +-15% above 1500 keV. The results of this initial study are given for a point source and a FPDS gas line collimator designed for PBF. Both experimental and calculated responses are given. Some of the reasons for the apparent differences between the calculated and experimental results are discussed. Modifications to the RAFFLE code were necessary in order to score the Ge detector count rate. The computer running times and man-hour costs are given along with recommendations for future modifications to RAFFLE which will improve the computation in the future. (ERA citation 09:006554)