Calculation of neutron die-away times in a large-vehicle portal monitor

Technical Report · Thu May 01 00:00:00 EDT 1980

DOI:https://doi.org/10.2172/5363135· OSTI ID:5363135

Lillie, R. A.; Santoro, R. T.; Alsmiller, Jr., R. G.

Monte Carlo methods have been used to calculate neutron die-away times in a large-vehicle portal monitor. These calculations were performed to investigate the adequacy of using neutron die-away time measurements to detect the clandestine movement of shielded nuclear materials. The geometry consisted of a large tunnel lined with He/sup 3/ proportional counters. The time behavior of the (n,p) capture reaction in these counters was calculated when the tunnel contained a number of different tractor-trailer load configurations. Neutron die-away times obtained from weighted least squares fits to these data were compared. The change in neutron die-away time due to the replacement of cargo in a fully loaded truck with a spherical shell containing 240 kg of borated polyethylene was calculated to be less than 3%. This result together with the overall behavior of neutron die-away time versus mass inside the tunnel strongly suggested that measurements of this type will not provide a reliable means of detecting shielded nuclear materials in a large vehicle. 5 figures, 4 tables.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• DOE Contract Number: W-7405-ENG-26
• OSTI ID: 5363135
• Report Number(s): ORNL/TM-7299; TRN: 80-010477
• Country of Publication: United States
• Language: English

Related Subjects

98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION
NEUTRON DETECTION
NUCLEAR MATERIALS DIVERSION
DETECTION
BORON COMPOUNDS
DECAY
HE-3 COUNTERS
NEUTRON FLUX
POLYETHYLENES
SHIELDING
TRUCKS
TUNNELS
MEASURING INSTRUMENTS
NEUTRON DETECTORS
ORGANIC COMPOUNDS
ORGANIC POLYMERS
POLYMERS
POLYOLEFINS
PROPORTIONAL COUNTERS
RADIATION DETECTION
RADIATION DETECTORS
RADIATION FLUX
VEHICLES
055001* - Nuclear Fuels- Safeguards
Inspection
& Accountability- Technical Aspects