The ANTECH Model 2072 Decommissioning Piece Monitor is a high efficiency passive

neutron counter designed for the measurement of plutonium contaminated size reduced

pieces arising from the decommissioning of nuclear plant and equipment. The system can

also be used to measure plutonium bearing material in storage containers.

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 Pu-240.

The measurement chamber can be installed outside of any Modular Containment System

or similar exclusion zone. This can be adjacent to a convenient bagging port through

which size reduced pieces are introduced for measurement. A closure plug is provided

for the top of the measurement chamber.

Plant measured isotopic ratios can be used by the software in order to convert 240Pueffective

mass to total Pu mass. Alternatively a suitable germanium gamma-ray detector can be

conveniently installed through the base polyethylene shield plug to interrogate the sample

and determine the Pu isotopic ratios independently using PC-FRAM or other isotopic

The neutron detection system consists of 72, He-3 tubes arranged in two concentric rings

of 36 tubes embedded in a polyethylene moderator; 18 sets of 4 tubes are connected to a

high voltage junction box containing an Amptek charge sensitive amplifier/discriminator

circuit and connections for high voltage, low voltage and signal cables. The detectors are

embedded in a polyethylene moderator, which includes a thickness of 230mm back

shielding for operation in relatively high neutron background environments. The outer

surface is covered in stainless steel cladding. The internal and external moderator sur-

faces are covered in cadmium to prevent thermalised neutrons from re-entering the sam-

ple measurement cavity.

The Decommissioning Piece Monitor can be used

with either the Advanced Multiplicity Shift Regis-

ter (AMSR) with INCC-32 software or the Time

Correlation Analyser (TCA). In either case the sys-

tem can be operated in conventional shift register

coincidence counting (reals) mode (with a calibra-

tion function), the absolute multiplicity counting

mode (histogram function) or totals counting mode.

ANTECH Model 2072H for horizontal operation

72 He-3 detector tubes, 25.4mm x 1.0m

Weight: 400kg approx

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Footprint, including handle and frame:

at 4 Atm

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Detection efficiency: ~28%

110cm long x 90cm wide x 140cm high

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Operating Voltage: ~1650 volts

Electrical connections:

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High voltage - SHV

Die-away time: ~40µs

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5Vsupply for head amps - BNC

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Minimum detection limit of between

Signal output - BNC

10 ­ 50mg 240Pueffective in coincidence

Mixer RS-232 output - 9 way male `D'

(reals) mode equivalent to between ~0.2

and 1.0g total Pu (military grade)