The ANTECH Neutron Passive Crate Counter (nPCC) has a typical detection efficiency

of ~30% with Cd filters deployed and ~40% with the internal Cd liner removed. It is used

for the determination of the 240Pu mass in TRU Waste transport containers. The Passive

Neutron Crate Counter can be configured to the customer's requirements to measure a va-

riety of waste boxes including B25 Crate or the Standard Waste Box.

The operation of the instrument is based on passive neutron counting of the correlated

neutrons arising from spontaneous fission of the even Pu nuclides, principally 240Pu. The

neutron detection system consists of multiple polyethylene moderated detector modules

each containing eight, 6.5 atmosphere 1-inch diameter 3He tubes. The tubes are con-

nected to junction boxes, which are hermetically sealed and contain not only the high

voltage distribution and charge collection circuitry, but also the AMPTEK model A-111

charge sensitive amplifiers. The detector modules are housed inside an outer shielding of

270 mm thickness of polyethylene.

The Passive Neutron Crate Counter is coupled with an Advanced Multiplicity Shift Reg-

ister (AMSR-150) that uses an optimised version of the LANL INCC code for cosmic-ray

reduction. This involves both multiplicity distribution truncation and veto counting of ad-

jacent detectors to reduce the cosmic-ray generated coincidence background.

The Passive Neutron crate Counter is available with `Add-a-Source' Cf-252 based matrix

correction capability, as an option. This is a well established technique for matrix correc-

tion and is appropriate where low count rates and small quantities of material are present

in the measurement chamber. 'Add-a-Source' complements matrix correction by neutron

multiplicity counting. The system consists of typically an 80 µCi 252Cf source deployed

on a `Teleflex' cable with associated shielding, motor drive and control.

The Passive Neutron Crate Counter can be operated in conventional shift register coinci-

dence counting (reals) mode (with a calibration function), the absolute multiplicity count-

ing mode (histogram function) or totals counting mode. Plant measured isotopic ratios can

be used by the software to convert 240Pueffective mass to total Pu mass.

Typically 272, 3He detector tubes at 6.5 Atmospheres, deployed around the crate or

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Detection efficiency typically ~30% with Cd filters deployed and ~40% with the in-

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ternal Cd liner removed

Operating Voltage: ~1650 volts

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Detector Module Die-away time: < 40µs

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Minimum detection limit of 92mg 240Pueffective in coincidence (reals) mode equivalent

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to between ~1.54 grams total Pu (military grade)

Weight: 4000 kg approximately

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Approximate Instrument Footprint: (L x W x H) 10' x 8' x 7'

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