Optimal Background Attenuation for Fielded Spectroscopic Detection Systems

Conference · Mon Dec 31 04:00:00 EST 2007

DOI:https://doi.org/10.1109/NSSMIC.2007.4437210· OSTI ID:947062

Robinson, Sean M; Ashbaker, Eric D; Schweppe, John E; Siciliano, Edward R

Radiation detectors are often placed in positions difficult to shield from the effects of terrestrial background gamma radiation. This is particularly true in the case of Radiation Portal Monitor (RPM) systems, as their wide viewing angle and outdoor installations make them susceptible to radiation from the surrounding area. Reducing this source of background can improve gross-count detection capabilities in the current generation of non-spectroscopic RPM’s as well as source identification capabilities in the next generation of spectroscopic RPM’s. To provide guidance for designing such systems, the problem of shielding a general spectroscopic-capable RPM system from terrestrial gamma radiation is considered. This analysis is carried out by template matching algorithms, to determine and isolate a set of non-threat isotopes typically present in the commerce stream. Various model detector and shielding scenarios are calculated using the Monte-Carlo N Particle (MCNP) computer code. Amounts of nominal-density shielding needed to increase the probability of detection for an ensemble of illicit sources are given. Common shielding solutions such as steel plating are evaluated based on the probability of detection for 3 particular illicit sources of interest, and the benefits are weighed against the incremental cost of shielding. Previous work has provided optimal shielding scenarios for RPMs based on gross-counting measurements, and those same solutions (shielding the internal detector cavity, direct shielding of the ground between the detectors, and the addition of collimators) are examined with respect to their utility to improving spectroscopic detection.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 947062
• Report Number(s): PNNL-SA-58117; 400904120
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ALGORITHMS
ATTENUATION
BACKGROUND RADIATION
COLLIMATORS
COMPUTER CODES
DETECTION
GAMMA RADIATION
MONITORS
National Security
OUTDOORS
PROBABILITY
RADIATION DETECTORS
RADIATIONS
SHIELDING
SHIELDS
STEELS
TRADE
background shielding
spectroscopic detectors