Year
2004
Abstract
Note: No final paper was submitted for the Proceedings. Spontaneous fission Cf-252 neutron sources are commonly used to calibrate and test the operating performance of portal monitors. Cf-252 is preferred over (alpha,n) sources for many operational and safety reasons, but most importantly can be designed to emit an energy-dependent spectrum that closely matches that of Pu-240. Pu-240 is the pre-dominant neutron emitter of plutonium metal and oxides. Because portal monitors and other border monitoring devices are designed to detect low neutron fluence rates at distances of 1-3 meters from the detector, several characteristics in the manufacture and decay of the source need to be understood and accounted for in order to make an accurate measurement of the performance: isotopic composition, age, traceability, angular dependence of the neutron flux, and design and manufacture of the moderating cover are examples. This paper describes these issues and presents the range of possible error terms in the utilization of these physically small, relatively weak, (104 n.s-1) neutron sources for calibration of portal monitors.