THERMAL NEUTRON MULTIPLICITY COUNTING OF SAMPLES WITH VERY LOW FISSION RATES*

When samples with very low fission rates are assayed using thermal neutron multiplicity counting, shift register electronics, and the moments formalism for the singles, doubles, and triples count rates, large counting statistics errors can occur in the triples rates because of cosmic ray events. These counting statistics errors can be greatly reduced using gate multiplicity analysis when cosmic ray events produce high multiplicity neutron bursts. The gate multiplicity analysis method, measurement data, and results are presented.