Calibrating Passive Neutron Multiplicity and Waste Counters Using Calibrated 252Cf Sources: Estimating aPu-Values Without Pu

摘要

252Cf sources are especially interesting for calibrating passive multiplicity counters without the need for Pu because: - they are genuinely point-like and being lightly encapsulated offer a nearly isotropic unperturbed fission spectrum of neutrons - for all practical purposes they can be considered as a pure source of spontaneous fission neutrons which considerably simplifies interpolation. That is the leakage self multiplication, ML, can be taken as unity and the ratio α of (α, n)-to-(SF, n) neutrons can be taken as zero. - it is a well studied multiplicity system with the factorial moments νi of the distribution P(ν) being well established. - the energy spectrum is similar to that of the spontaneous spectra of the Pu isotopes - it is readily available with well known outputs , Y, determined absolutely by reference to Mn-baths operated by National Standards Laboratories In this work we exploit these features in the framework of the point-model interpretational equations discussed in ASTM C 1500 ‘Standard Test Method for Nondestructive Assay of Plutonium by Passive Neutron Multiplicity Counting’. In particular we: extend the equations to include the delayed neutron contribution showing how to extract the gate utilization factors (GUFs) accurately from the data available; extend the solutions given in the Appendices to cases where the Triples GUF is not equal to the square of the Doubles GUF; and, illustrate how to project 240Pueff performance from measured 252Cf.