The ANTECH Model 4200-600 is an enhanced efficiency active/passive neutron counter

designed for the measurement of plutonium and uranium in nuclear waste and housed in

an ISO shipping container.

In active totals mode, pulses of neutrons are used to interrogate a waste drum placed in

the measurement chamber. A neutron generator is pulsed at 100 Hz producing 14-MeV

neutrons. The neutrons are slowed down in graphite providing a source of thermal neu-

trons that cause induced fission in the 235U and 239Pu in the waste. Each pulse generates

approximately 1 x 106 neutrons. Cadmium shielded detector packages are used to meas-

ure the prompt fission neutrons (from induced fission) in a time period (~500 µs) when

neutrons from the initial generator burst have been cleared from the fast detector pack-

ages. Additional 3He flux monitors are placed in the measurement chamber and provide a

measure of the interrogating neutron intensity and its die away characteristics. A later

time period is used to determine the background due to de-

layed neutron production from fission products and from

any spontaneous fission nuclides present. The fissile mass

is proportional to the net fissile signal normalized to the in-

terrogating flux.

Passive mode operation uses conventional neutron counting

of the correlated neutrons arising from spontaneous fission

of the even Pu nuclides, principally Pu-240. Plant measured

isotopic ratios (from high resolution gamma spectrometry)

can be used by the software in order to convert 240Pueffective

mass to total Pu mass.

The neutron detection system consists of 88, 3He tubes em-

bedded in a cadmium clad polyethylene moderator arranged

in 18 fast detector packages (three per side). Each package

is 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. Polyethylene back shielding is provided to reduce the ef-

fects of ambient background. The outer surface is covered in stainless steel cladding.

The graphite liner is clad in aluminium.

The Model 4200-600 can be operated in conventional totals active mode or the more ad-

vanced Fission Fission neutron Correlation coincidence counting (reals) mode. This lat-

ter mode reduces the amount of effort required to calibrate the measurement system.

88 3He detector tubes, 25.4mm diameter at 4 Atmosphere pressure

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Die-away time fast detector packages: ~40µS

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Die-away time (chamber): ~ 1.0mS

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Passive mode detection efficiency approx. 12% (empty chamber)

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Weight: 9500 kg approximately

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Footprint: 1710mm x 2417mm x 1702mm excluding conveyor/loading platform

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Measurement Chamber size: 1250mm x 850mm x 850mm

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Services: Electrical 240v or 110v AC

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