Year
2012
Abstract
The shortage of helium-3 (3He) has created a need for alternative neutron detectors for various applications. One of the neutron detection systems affected by the decreased availability of 3He is multiplicity counters. Traditionally, multiplicity counters have been designed with high pressure 3He proportional counters (4 to 10 atm) to meet the high efficiency and short die-away time performance requirements. An effort to identify a potential 3He replacement for multiplicity counters is being undertaken at Pacific Northwest National Laboratory. The study is considering mature, existing technologies that are suitable for immediate use; boron tri-fluoride (BF3) filled proportional counters, boron-10 (10B) lined tubes, and lithium-6 (6Li) coated fibers. The project encompasses several phases, the first of which is exploring various multiplicity counter configurations with the alternative detectors. The optimal configuration, within certain physical constraints on system size, for the different 3He alternative detectors is being established with Monte Carlo simulations. The multiplicity counter designs are being constructed to maximize the amount of neutron detection medium within the system, while maintaining reasonable dimensions. The configurations are being evaluated based on the efficiency and die- away time of the system. The variations being considered for the BF3 gas filled proportional counters are changes in the tube diameter and the fill gas pressure. The changes to the 10B-lined tubes being simulated are different tube diameters and lining thicknesses. The change to the systems designed with 6Li coated fibers is the number of layers of detection medium. The highest performing configuration for each variation has been determined, and the results are reported. The simulations are being validated against basic efficiency measurements made with representatives of the different detectors.