CF Neutron Time of Flight Transmission for Material Identification for weapons Trainers

Conference · Thu Jul 21 00:00:00 EDT 2011

OSTI ID:1035827

Mihalczo, John T. ^[1]; Valentine, Timothy E. ^[1]; Blakeman, Edward D. ^[1]; Pare, Victor ^[1]

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1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)

The neutron transmission, elastic scattering, and non-elastic reactions can be used to distinguish various isotopes. Neutron transmission as a function of energy can be used in some cases to identify materials in unknown objects. A time tagged californium source that provides a fission spectrum of neutrons is a useful source for neutron time-of-flight (TOF) transmission measurements. Many nuclear weapons trainer units for a particular weapons system (no fissile, but of same weight and center of gravity) in shipping containers were returned to the National Nuclear Security Administration Y-12 National Security Complex in the mid 1990s. Nuclear Materials Identification System (NMIS) measurements with a time tagged californium neutron source were used to verify that these trainers did not contain fissile material. In these blind tests, the time distributions of neutrons through the containers were measured as a function of position to locate the approximate center of the trainer in the container. Measurements were also performed with an empty container. TOF template matching measurements were then performed at this location for a large number of units. In these measurements, the californium source was located on one end of the container and a proton recoil scintillator was located on the other end. The variations in the TOF transmission for times corresponding to 1 to 5 MeV were significantly larger than statistical. Further examination of the time distribution or the energy dependence revealed that these variations corresponded to the variations in the neutron cross section of aluminum averaged over the energy resolution of the californium TOF measurement with a flight path of about 90 cm. Measurements using different thicknesses of aluminum were also performed with the source and detector separated the same distance as for the trainer measurements. These comparison measurements confirmed that the material in the trainers was aluminum, and the total thickness of aluminum through the trainers was determined. This is an example of how californium transmission TOF measurements can be used to identify materials.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1035827
• Resource Relation: Conference: 52nd Annual INMM Meeting, Desert Palm, CA (United States), 17-21 Jul 2011
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ALUMINIUM
CALIFORNIUM
CONTAINERS
CROSS SECTIONS
DISTRIBUTION
ELASTIC SCATTERING
ENERGY DEPENDENCE
ENERGY RESOLUTION
FISSILE MATERIALS
FISSION
IDENTIFICATION SYSTEMS
NATIONAL SECURITY
NEUTRON SOURCES
NEUTRONS
NUCLEAR WEAPONS
PHOSPHORS
PROTONS
SECURITY
THICKNESS
WEAPONS
Nuclear Criticality Safety Program (NCSP)
Californium Transmission TOF Measurements
Materials Identification
Unknown Objects