Developing a Methodology for Characterization of Building Materials' Natural Radiation Background and Integration into an MCNP Model for Radiation Portal Monitoring Systems

Year
2012
Author(s)
William S. Charlton - Nuclear Security Science & Policy Institute, Texas A&M University
Jake Livesay - Oak Ridge National Laboratory
Tyler Guzzardo - Oak Ridge National Laboratory
Matthew B. Fitzmaurice - Nuclear Security Science and Policy Institute, Texas A&M University
Alexander A. Solodov - Nuclear Security Science and Policy Institute, Texas A&M University
Craig M. Marianno - Nuclear Security Science and Policy Institute, Texas A&M University
Abstract
This paper describes a methodology for quick and efficient determination of the specific activity and composition of building materials surrounding a radiation portal monitor (RPM) to predict background levels in an RPM. This methodology builds on previous work by Ryan et al 1 by generating material and source cards for a detailed Monte Carlo N-Particle (MCNP) deck, based on an experimental RPM setup to predict the overall gamma background at the site. Gamma spectra were acquired from samples of building materials and analyzed to determine the specific activity of the samples. A code was developed to estimate the elemental composition of building materials using the gamma transmission rates of the samples. These results were compared to previous Neutron Activation Analysis (NAA) on the same samples. It was determined that densitometry provided an appropriate estimation of the samples elemental composition. Then using the specific activity and material composition, an MCNP deck was used to predict the gamma background levels in the detectors of a typical RPM. These results were compared against actual measurements at the RPM site.