Accuracy improvement of a simulation model of a radiation portal monitor by correcting dead-time effect

Abstract

Thousands of radiation portal monitors (RPMs) have been deployed around the world to detect radioactive materials that are outside of regulatory control. The detection capability of the RPMs can be evaluated by conducting a field test with various radioactive materials. However, field tests are limited because the RPMs are operated 24 h a day. The Monte Carlo N-Particle (MCNP) transport code provides an alternative. To evaluate the performance of the RPM with MCNP-based simulation model, the simulation results should be experimentally validated and the measurement result for the validation should be corrected for dead time effect. In this study, an MCNP-based RPM simulation model was developed and the accuracy of the RPM simulation model was improved by correcting dead-time effect. Static and dynamic measurements were conducted and the dead-time correction for the measurement data was factored in. With the static measurement data, the simulation model was developed and the comparing results with the static measurement data show that it satisfied an average relative difference of less than 10%. The simulation model was validated with 17 dynamic measurement datasets and the validation results show that the average relative differences are also within 10% even though the experimental conditions of the static and dynamic measurements were different.