A Nearly-Four-Pi Liquid Scintillation Counter for Bursts of Fast Neutrons

This liquid scintillation counter detects 14 mev neutrons by both proton-recoil and neutron-proton capture processes. It is designed to measure fast neutrons which occur in a single burst of a few microseconds duration, a burst which may contain anywhere from 100 to 100,000 neutrons. The counter is 36 inches in diameter, 36 inches long, and has an axial access cylinder 12 inches in diameter. It contains 475 liters of triethylbenzene, 2.5 grams per liter of p-terphenyl and 0.02 grams per liter of POPOP. Scintillations are detected by 20 Dumont Type 6364 multiplier phototubes. Four tubes are used as proton-recoil detectors and 16 are used as neutron-proton capture detectors. The counter was completed in January 1959, and has shown high reliability and only a relatively small change in sensitivity since it was first calibrated.