DEVELOPMENT OF NEUTRON MULTIPLICITY COUNTERS FOR SAFEGUARDS ASSAY

This paper reports on the development of a new generation of neutron multiplicity counters for assaying impure plutonium. The new counters will be able to obtain three measured parameters from the neutron multiplicity distribution and will be able to determine sample mass, multiplication, and (α,n) reaction rate, making it possible to obtain a more matrix-independent assay of moist or impure materials. This paper describes the existing prototype multiplicity counters and evaluates their performance using assay variance as a figure of merit. The best performance to date is obtained with a highefficiency, low die-away-time thermal neutfon counter with shift-register electronics.