Other

University of California

Merlyn S Krick

Steven C Bourret

James Edward Stewart

Howard O Menlove

Martin R Sweet

This invention relates to both the apparatus and method for increasing the sensitivity of measuring the amount of radioactive material in waste by reducing the interference caused by cosmic ray generated neutrons. The apparatus includes: (a) a plurality of neutron detectors, each of the detectors including means for generating a pulse in response to the detection of a neutron; and (b) means, coupled to each of the neutrons detectors, for counting only some of the pulses from each of the detectors, whether cosmic ray or fission generated. The means for counting includes a means that, after counting one of the pulses, vetos the counting of additional pulses for a prescribed period of time. The prescribed period of time is between 50 and 200 &mgr;s. In the preferred embodiment the prescribed period of time is 128 &mgr;s. The veto means can be an electronic circuit which includes a leading edge pulse generator which passes a pulse but blocks any subsequent pulse for a period of between 50 and 200 &mgr;s. Alternately, the veto means is a software program which includes means for tagging each of the pulses from each of the detectors for both time and position, means for counting one of the pulses from a particular position, and means for rejecting those of the pulses which originate from the particular position and in a time interval on the order of the neutron die-away time in polyethylene or other shield material. The neutron detectors are grouped in pods, preferably at least 10. The apparatus also includes means for vetoing the counting of coincidence pulses from all of the detectors included in each of the pods which are adjacent to the pod which includes the detector which produced the pulse which was counted.

Cosmic ray neutron background reduction using localized coincidence veto neutron counting

This invention relates to a method and apparatus for improving the precision of at least one of neutron coincidence counting and neutron multiplicity counting. The method includes the steps of: (1) sampling the real and accidental coincident pulses at the incoming pulse rate; and (b) sampling the accidental coincidences at a clock rate, wherein the clock rate is much faster than the pulse rate. The clock rate is faster than the pulse rate by a factor of 5 to 10 (in the preferred embodiment, approximately 4 MHz). The apparatus for improving the precision of neutron coincidence counting includes: (a) a shift register; (b) an up-down counter coupled to the shift register; (c) an R&plus;A accumulator coupled to the up-down counter; (d) an A accumulator coupled to the up-down counter; (e) a strobe, the strobe coupled to the R&plus;A accumulator but not to the A accumulator; (f) a clock, the clock coupled to the A accumulator but not to the R&plus;A accumulator, the clock having a rate which is much faster than the pulse rate; and (g) apparatus for reconciling the independent counting of the A accumulator with that of the R&plus;A accumulator. For improving the precision of multiplicity counting the apparatus includes an R&plus;A multiplicity accumulator and an A multiplicity accumulator, The R&plus;A multiplicity accumulator is connected to the up-down counter and the strobe, but not to the clock. The A multiplicity accumulator is coupled to the up-down counter and the clock, but not to the strobe. The clock rate is faster than the pulse rate by a factor of 5-10 (in the preferred embodiment, approximately, 4 MHz). The apparatus also includes apparatus for accumulating the total number of pulses, which is coupled to the strobe and the reconciling apparatus.

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Los Alamos, NM, United States of America

Merlyn S Krick