Year
2003
Abstract
Portable real-time neutron detection systems require sensors that have a high sensitivity, minimal response to vibration, good temperature stability, small size and low weight. These parameters are particularly important for systems that are worn on the body as a personal radiation alarm. In selecting a neutron detector, one must compare advantages and disadvantages of the technologies used today. In the following, we evaluate the factors above and compare a 3He proportional counter and 6Li loaded scintillator. The design of a 3He proportional counter is presented with details of the electrical and nuclear characteristics that make it attractive for the intended purpose. Each of the performance requirements described has a significant effect on the choice of the technology. High sensitivity is desirable so that detection and alarm limits may be established at levels below which would expose the wearer to immediate harm. However, the need for high sensitivity conflicts with the requirement for small size and low weight. The neutron absorption cross section of the material selected for neutron detection and the efficiency of extracting the deposited energy in the presence of interfering noise from gamma rays, vibration induced noise and other environmental effects such as temperature variation play a major role in selecting the most appropriate technology. In the comparison, a 3He proportional counter has been fabricated with a sensitivity of 4.2 cps/nv, diameter of only 1.59 cm, length of 6.03 cm and weight of only 17 gm. In addition to being highly sensitive, the pulse height spectrum shows that the device has excellent discrimination against gamma rays. The response to vibration is measured and compared to scintillator based neutron detectors. The performance under vibrational stimulus is tabulated for the 3He proportional counter and a ruggedized scintillator package designed for oil well logging. The vibration responses of the detector assemblies are quantified in relation to the shock and vibration stimuli that might be encountered while driving or riding in a vehicle, walking or running.