The ANTECH Model 2108 Plutonium Scrap Multiplicity Counter (PSMC) is a high

efficiency passive neutron counter designed for measuring the multiplicity of neutron

emissions from the spontaneous fission and induced fission of plutonium bearing samples of

scrap and residues. The PSMC was developed by the Los Alamos National Laboratory for

safeguards and inventory control purposes. Conventional passive neutron coincidence

counting of scrap & residues give rise to significant biases since the Pu present is often in

lumped form and mixed with significant quantities of low-z number impurities. The high α-

ratio causes a general increase in the apparent correlated response through induced fission

reactions which can lead to significant biases. In multiplicity counting, the number of signal

multiplets (the signal frequency

distribution) is measured in the neutron

pulse train. From the moments of the

neutron probability distribution it is

possible to determine the number of

neutron totals, the number of correlated

neutron pairs and the number of

correlated neutron triples. When one of

the variables is known (or can be

inferred), the data analysis employs a

point source model to perform a four

parameter analysis based on the

frequency distribution to solve for the

spontaneous fission rate, Fs (and hence

the 240Pueffective mass), the detection probability  The PSMC can be operated using either the

(ε), the (α,n) source term (S α) or the neutron   Time Correlation Analyzer or the Advanced

Multiplicity Shift Register.

multiplication, M as appropriate.

80 × 3He tubes (25.4mm outer diameter × 711 mm active tube length, 4 atmos-

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pheres fill pressure) arranged in four concentric rings

Cylindrical HDPE moderator

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Fast Amptek A-111 based amplifier/discriminator based junction box

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Integrated ANTECH De-randomizing Buffer Mixer Counter

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HV Bias setting ~1650 V

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Gate Width setting typically 64 µ s

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Pre-delay 4 µ s

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Expected sensitivity ~150 reals/s/g 240Pu(effective)

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Weight ~400kg

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Dimensions 950 mm (37.4 in.) × 650 mm (25.6 in.) × 650 mm (25.6 in.)

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