Terrestrial Background Reduction in RPM Systems by Direct Internal Shielding

Conference · Wed Nov 19 04:00:00 EST 2008

DOI:https://doi.org/10.1109/NSSMIC.2008.4774646· OSTI ID:965161

Robinson, Sean M; Ashbaker, Eric D; Schweppe, John E

Gamma-ray detection systems that are close to the earth or other sources of background radiation often require shielding, especially when trying to detect a relatively weak source. One particular case of interest that we address in this paper is that encountered by the Radiation Portal Monitors (RPMs) systems placed at border-crossing Ports of Entry (POE). These RPM systems are used to screen for illicit radiological materials, and they are often placed in situations where terrestrial background is large. In such environments, it is desirable to consider simple physical modifications that could be implemented to reduce the effects from background radiation without affecting the flow of traffic and the normal operation of the portal. Simple modifications include adding additional shielding to the environment, either inside or outside the apparatus. Previous work [2] has shown the utility of some of these shielding configurations for increasing the Signal to Noise Ratio (SNR) of gross-counting RPMs. Because the total cost for purchasing and installing RPM systems can be quite expensive, in the range of hundreds of thousands of dollars for each cargo-screening installation, these shielding variations may offer increases in detection capability for relatively small cost. Several modifications are considered here in regard to their real-world applicability, and are meant to give a general idea of the effectiveness of the schemes used to reduce background for both gross-counting and spectroscopic detectors. These scenarios are modeled via the Monte-Carlo N-Particle (MCNP) code package [1] for ease of altering shielding configurations, as well as enacting unusual scenarios prior to prototyping in the field. The objective of this paper is to provide results representative of real modifications that could enhance the sensitivity of this, as well as the next generation of radiation detectors. The models used in this work were designed to provide the most general results for an RPM. These results are therefore presented as general guidance on what shielding configurations will be the most valuable for a generalized RPM, considered in light of their economic and geometric possibility in the real world.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 965161
• Report Number(s): PNNL-SA-63479; 400904120
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
BACKGROUND RADIATION
Background Reduction
DETECTION
DOLLARS
Direct Internal Shielding
ECONOMICS
MODIFICATIONS
MONITORS
RADIATION DETECTORS
RADIATIONS
RPM Systems
SCREENS
SENSITIVITY
SHIELDING
SIGNAL-TO-NOISE RATIO
Terrestrial