Active Well Coincidence Counter

Active Mode

For uranium measurements the N2442 is used in Active Mode. Two americium-lithium sources are inserted (one in the base and one in the plug unit) and the system is operated in random driver mode. Uncorrelated neutrons produced by the Am-Li sources induce fission in ²³⁵U samples in the measurement chamber. The coincidence counter electronics of the ANTECH N2000 Universal Neutron Counter (UNC) can be used to determine the coincidence count
rate, which is attributable to the induced fission in the ²³⁵U. Using this method the mass of uranium is readily determined.

Two action modes are available depending on the size of the ²³⁵U sample:

1. 1. 1. 1. 1. Thermal Active Mode is employed to measure low-enriched uranium materials. In this mode the sleeve and end plug cadmium coverings are removed. The detection level of this mode is approximately 1 gm of ²³⁵U.
            2. Fast Active Mode is employed to measure 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 23 gm of ²³⁵U.

Passive Mode

In Passive Mode the americium-lithium sources are removed and the N2442 can function either as a neutron coincidence counter or a neutron multiplicity counter, using the appropriate features of most commercially available neutron coincidence and multiplicity counters.

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 measurements.