The curved slab neutron coincidence slab counter measures the plutonium content of the sample by detecting coincidence neutrons from the spontaneous fission of the even numbered isotopes of plutonium. The counter is designed to make either quantitative or go/no-go measurements. A JSR-12 or JSR-14 Neutron Coincidence Analyzer is required for coincidence counting (ordered separately).
The counter is comprised of four separate slab counters. These counters are curved through 90° and may be fitted together to form a passive well counter. Each section of the counter contains eight 91 cm (35.8 in.) 3He proportional tubes forming a single detector bank. The output from each of these detector banks is daisy chained, providing a single TTL signal out to the shift register. When configured in its smallest sample geometry (i.e. the four slabs are in contact) the WM3500 counter provides an overall efficiency of 19.4%. As the sections are positioned further apart, the efficiency decreases. The full counter has a height of 114 cm (44.9 in.) and forms a circle with inner diameter of 54 cm (21.3 in.) and has an outer diameter of approximately 86 cm (33.9 in.). For the most accurate results the sample should be placed on a pedestal to center it vertically within the counter. Since this counter does not have end plugs, the axial response will fall quickly as the source is moved near the ends of the counter.