PASSIVE NEUTRON MULTIPLICITY COUNTING
N. Ensslin, M. S. Krick, D. G. Langner, M. M. Pickrell, T. D. Reilly, and J. E. Stewart
Purpose of the Chapter
A nondestructive assay (NDA) technique for plutonium, called passive neutron multiplicity
counting, has been developed as an extension of neutron coincidence counting (Ref. 1).
technique has led to the design and fabrication of neutron multiplicity counters, one of which is
pictured in Figure 6.1.
The development of new neutron counters has been accompanied by
advances in data-processing electronics, analysis algorithms, and data-analysis software.
Development activities have been funded primarily by the Department of Energy (DOE) Office
of Security Policy, Technology Development Branch.
The new technology has led to
significantly better measurement accuracy for plutonium metal, oxide, scrap, and residues.
Photo of the Plutonium Scrap Multiplicity Counter, used for
accurate assays of plutonium metal, oxide, mixed oxide, or scrap .
This chapter describes the principles of multiplicity counter design, electronics, and
Existing counters are surveyed, and their operating requirements and procedures
Current applications to different plutonium material types are described and
estimates of the expected assay precision and bias are given.
Definition of Neutron Multiplicity Counting
Multiplicity is a word with a multiplicity of meanings!
Our use of the word begins with the
fact that an important NDA signature for plutonium is spontaneous fission, leading to the nearly
simultaneous emission of multiple, indistinguishable neutrons. The number of neutrons emitted
in spontaneous fission can vary from zero to eight. The distribution of the number of neutrons is