The Active Well Coincidence Counter (AWCC) is a transportable high-efficiency counter

for the measurement of both uranium and plutonium. Originally developed by the Los

Alamos National Laboratory (LANL), the ANTECH variant contains the basic LANL

ideas with added performance-enhancing features. These include:

·  De-randomising buffer mixer circuit to reduce count losses

·  Built in totals counter associated with each amplifier channel

·  Robust mechanical design including lifting fixtures

For uranium measurement the AWCC is used in Active Mode. Two americium-lithium

neutron sources are inserted ­ one in the base and one in the plug unit ­ and the AWCC is

operated in random driver mode. Uncorrelated neutrons produced by the Am-Li sources

induce fission in U-235 samples in the measurement chamber. The coincidence counter

electronics of the ANTECH Advanced Multiplicity Shift Register can be used to deter-

mine to coincidence count rate, which is attributable to the induced fission in U-235. Us-

ing this method the mass of uranium is readily determined.

Two Action Modes are available depending on the size of the U-235 sample.

The AWCC in Thermal Active Mode is most appropriate for measuring low-enriched

uranium materials. In this mode the sleeve and end plug cadmium coverings are re-

moved. The detection level in this mode is approximately 1gm of U-235.

Fast Active Mode is employed for the measurement of highly enriched material such as

uranium metal, uranium thorium fuel and LWR fuel pellets. In this mode the cadmium

plates and sleeve are inserted and the detection limit is approximately 23gm of U-235.

In Passive Mode the Am-Li neutron sources are removed and the AWCC can function

either as a neutron coincidence counter or a neutron multiplicity counter, again using the

appropriate features of the ANTECH AMSR. The detector measurement chamber can be

enlarged by removing the two internal polyethylene disks and the nickel reflector. It can

also be operated in the horizontal position with the end plugs removed and with a material

test reactor (MTR) holder in position for the measurement of uranium in MTR measure-

Am-Li sources: 4.8 x 10,000 n/sec (2

Electrical connections:

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High voltage - SHV

Detection efficiency: 26% to 31%

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5V supply for head amlifiers - BNC

High Voltage: 1,680 volts

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Signal output - BNC

Mixer RS-232 output - 9w male 'D'

Weight: 130kg approx

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Overall envelope including handle and

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frame: 71.1cm long x 63.5cm wide x

104cm high

Adjustable measurement chamber:

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20.6cm high x 22.9cm diam. (8.1" x 9")