Year
2004
Abstract
There is currently a tremendous effort underway to develop and deploy sophisticated neutron monitoring systems for homeland defense, placed strategically at ports and major transport arteries throughout the US. To meet the growing demands of Home Land Defense and traditional applications, the use of cylindrical 3He filled proportional counters in neutron counting applications is set to rise. Gas-filled cylindrical proportional counters for the detection of thermal neutrons have been used successfully for many years but the expertise is concentrated in traditional areas and not readily accessible to this new and growing need. Applications specialists are faced with the challenge of comparing and selecting detectors of contrasting types, anode material, anode diameter, tube dimensions, gas mixture, fill pressures and the like, in order to achieve a targeted performance. In this paper we offer guidance to designers and users so that they may have a better understanding of the factors which are important in the deployment of these detectors for homeland defense. Operational topics presented include: specifying the thermal neutron sensitivity, counter microphonics, RF pickup, export control, transportation and handling. It is conventional for proportional counter manufacturers to quote in their product catalogs the neutron sensitivity in units of cps/nv. The definition and utility of this value is usually not explained adequately. It is frustrating to discover, upon examination of the product literature, that neutron sensitivity values for counters one would expect to have nominally similar performance characteristics can differ quite markedly. One is left wondering whether these differences are genuine or merely an artifact of how the term sensitivity has been applied. We set out from first principles the meaning of neutron sensitivity, explain with examples how it may be calculated, and discuss its value in practical situations.