Pyrochemical Multiplicity Counter Development
Author | : |
Publisher | : |
Total Pages | : 6 |
Release | : 1991 |
Genre | : |
ISBN | : |
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Impure plutonium-bearing materials from pyrochemical processes often display both significant self-multiplication and variable ([alpha], n) reaction rates. Standard neutron coincidence counting techniques usually fail to accurately measure these materials. Neutron multiplicity counters measure the third moment of the neutron multiplicity distribution and thus make it possible to deduce the fertile plutonium mass of a sample even when both the self-multiplication and the ([alpha], n) reaction rate are unknown. A multiplicity counter suitable for measuring pyrochemical materials has been designed and built. This paper describes the results of characterization studies for the new counter. The counter consists of 126 helium-3 tubes arranged in 4 concentric rings in a polyethylene moderator; the average spacing between the tubes is 1.59 cm. The end plugs for the counter are made of graphite, and the 24.1- by 37.5-cm sample cavity is cadmium lined. The counter consists of two distinct halves from which the neutron counts are summed. The counter is capable of operation in either a freestanding mode with the two halves coupled together by an external cabinet or in a glove-box mode with the two halves placed around a glovebox well and then mated. For a 252Cf source centered in the sample cavity, the measured efficiency of the new multiplicity counter is 57.7% and its die-away time is 47.2[mu]s. 8 refs., 9 figs.