MCNPX Simulation Study of STRAW Neutron Detectors
A novel prototype fission meter is being designed at National Security Technologies, LLC, using a thin uniform coating (only 1 micron thick) of {sup 10}B as a neutron converter inside a large array of thin (4 mm diameter) copper tubes. The copper tubes are only 2 mils thick, and each holds the stretched anode wire under tension and high voltage. The tubes are filled with proportional counter gas (a mixture of 90%/10% of Ar/CO{sub 2}). The tubes operate in proportional counter mode and attract mobile charged particles ({alpha}'s) created in the nuclear interaction {sup 10}B(n, {sup 4}He){sup 7}Li. However, a single tube has about 1/7th the sensitivity of a {sup 3}He tube. Modeling is required to determine if enough such tubes could be placed in a neutron detection assembly of the current size to give comparable sensitivity to {sup 3}He. Detectors lined with {sup 10}B lie between {sup 3}He and {sup 10}BF{sub 3} proportional counters and fission chambers in terms of neutron detection efficiency and gamma ray insensitivity. The mean free path of thermal neutrons in {sup 10}B is about 18 {micro}m. It takes about 60 {micro}m of {sup 10}B layer to completely stop thermal neutrons, but the energetic {alpha}-particles generated in the reaction have a range of only 3.3 {micro}m in {sup 10}B environment - hence the thin layer of boron coating on the copper tube. The prototype design is shown in Figure 1. It consists of two panels of three staggered rows of 500-mm-long, 4-mm-diameter straws, with 20 in each row, embedded in 30-mm-thick high density polyethylene (HDPE). The project demonstrates a new application of thin neutron and gamma converter technique (1 micron thin {sup 10}B coated copper tube). It exploits fast timing from multiple straw detectors to count multiplicity of both gamma and neutrons from fissioning materials. The objective is to find a near-term replacement of {sup 3}He gas in neutron detection and measurement (with a very large neutron detection area). All the solid-state detectors developed thus far are small and inefficient. The thin size of the straws provides imaging capability with high enough resolution for radiation emitting sources. The prototype will provide the first aerial neutron detection system with directional sensitivity.
- Research Organization:
- National Security Technologies, LLC (United States)
- Sponsoring Organization:
- USDOE; USDOE National Nuclear Security Administration (NA)
- DOE Contract Number:
- DE-AC52-06NA25946
- OSTI ID:
- 992613
- Report Number(s):
- DOE/NV/25946-866; TRN: US1100412
- Resource Relation:
- Conference: 2010 Symposium on Radiation Measurement and Applications (SORMA XII), May 24-28, 2010
- Country of Publication:
- United States
- Language:
- English
Similar Records
Estimation of Performance of an Active Well Coincidence Counter Equipped with Boron-Coated Straw Neutron Detectors - 13401
Nuclear Structure of Radioactive Neutron-Rich Nuclei with 4pi Detector Arrays
Related Subjects
ANODES
CHARGED PARTICLES
COPPER
FISSION CHAMBERS
MEAN FREE PATH
NATIONAL SECURITY
NEUTRON CONVERTERS
NEUTRON DETECTION
NEUTRON DETECTORS
NEUTRONS
POLYETHYLENES
PROPORTIONAL COUNTERS
RADIATIONS
SENSITIVITY
SIMULATION
STRAW
THERMAL NEUTRONS
MCNPX
straw
neutron detector