A Portable Neutron Dose Equivalent Meter

A portable, battery-operated fast neutron monitor has been developed for use at reactors and accelerators. The instrument employs a polyethylene loaded proportional counter and reads directly in biologically equivalent units for neutrons from .1 MeV to over 15 MeV on eight scales ranging from 2 mrem per hour to 6000 mrem per hour. On the lower ranges, the input pulses are integrated for electronically determined time intervals, while on the higher ranges a ratemeter mode of operation is employed. All of the electronics, including the 1400 V power supply for the protonrecoil type detector requires only 25 milliwatts of power, permitting about 500 hours of continuous operation from a small 7 V mercury battery. Electronic voltage regulation and the use of field-effect transistors in the integrating and timing circuits provide a stability of calibration far beyond that normally associated with portable survey instruments.