Monte Carlo Simulations of Prototype Radioxenon Beta-gamma Counting Systems

Abstract

One of the recently established methods for monitoring a Comprehensive nuclear Test Ban Treaty (CTBT) is the collection and analysis of radioxenon isotopes as collected and measured by International Monitoring System (IMS) stations. Radioxenon isotopes are produced from several sources including nuclear power generating stations, medical isotope production and nuclear test detonations. Each of the potential sources produces a characteristic energy spectrum that can interfere with that of another source. Therefore, to be able to accurately calculate isotopic concentrations, it is important to be able to distinguish between the different isotopes which share regions of interest in the beta‐gamma energy domain. Veridian Systems has developed a method that utilizes the known resolution response from a particular detector system and Monte Carlo simulations to predict the interference from other isotopes into a region of interest. This allows the system to be setup with more well defined regions of interest and a better understanding of the interference parameters. This method can also lead to a more accurate determination of isotopic concentrations and a lower minimum detectable concentration. Along with determining the isotopic concentrations another Monte Carlo simulation has been developed that examines each particle track history in a simulation to determine the coincidence efficiency of the system. This efficiency is based on coincident interactions and deposited energy in both gamma and beta detectors from a single gamma source. The process and results for the Monte Carlo simulations are discussed and compared with experimental data.