Directional measurements for sources of fission neutrons

Technical Report · Mon Nov 01 04:00:00 EST 1993

DOI:https://doi.org/10.2172/10107212· OSTI ID:10107212

Byrd, R C; Auchampaugh, G F; Feldman, W C

Although penetrating neutron and gamma-ray emissions arguably provide the most effective signals for locating sources of nuclear radiation, their relatively low fluxes make searching for radioactive materials a tedious process. Even assuming lightly shielded sources and detectors with large areas and high efficiencies, estimated counting times can exceed several minutes for source separations greater than ten meters. Because determining the source position requires measurements at several locations, each with its own background, the search procedure can be lengthy and difficult to automate. Although directional measurements can be helpful, conventional collimation reduces count rates and increases the detector size and weight prohibitively, especially for neutron instruments. We describe an alternative approach for locating radiation sources that is based on the concept of a polarized radiation field. In this model, the presence of a source adds a directional component to the randomly oriented background radiation. The net direction of the local field indicates the source angle, and the magnitude provides an estimate of the distance to the source. The search detector is therefore seen as a device that responds to this polarized radiation field. Our proposed instrument simply substitutes segmented detectors for conventional single-element ones, so it requires little or no collimating material or additional weight. Attenuation across the detector creates differences in the count rates for opposite segments, whose ratios can be used to calculate the orthogonal components of the polarization vector. Although this approach is applicable to different types of radiation and detectors, in this report we demonstrate its use for sources of fission neutrons by using a prototype fast-neutron detector, which also provides background-corrected energy spectra for the incident neutrons.

• Research Organization: Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 10107212
• Report Number(s): LA--12633-MS; ON: DE94002888
• Country of Publication: United States
• Language: English

Related Subjects

440101
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
COMPUTERIZED SIMULATION
DIRECTIONAL RADIATION DETECTORS
GENERAL DETECTORS OR MONITORS AND RADIOMETRIC INSTRUMENTS
NEUTRON DETECTION
NEUTRON DETECTORS
POLARIZATION
RADIATION SOURCES
SHIELDING