Digital environmental monitor

An instrument has been designed to replace the Dynamic Condenser Electrometer to measure the background radiation levels at the boundaries of Brookhaven National Laboratory. The detector is a 2'' x 2'' tin loaded plastic scintillator, whose energy response is air equivalent, coupled to a bialkali cathode 2'' photomultiplier tube operated in the direct current mode. The output of the photomultiplier is digitized by a current to frequency converter, and the resultant pulses fed to a scaler. The system is programmed to calibrate itself once an hour to compensate for changes in photomultiplier tube gain to changes in temperature. During the calibration cycle a number, which is a function of the system's gain, is generated and held in a register, and is then used to weight the data accumulated between calibration cycles. The output data is stored on a six digit non-resetting printing register. The register, which can be programmed to print at any time interval desired, also prints the day of the year, time of day and station number. The instrument, which is calibrated to give 10 counts per μR, has a minimum sensitivity of 1 μR/hr and was designed so that it will not saturate at 10 mR/hr, making it useful in the event of an accidental high level activity release. The digital logic is accomplished by the use of integrated circuits mounted on printed circuit boards housed in NIM modules. The detector is housed in an aluminum weather tight container. Two of the units have been in operation for over a year with no significant maintenance problems. (U.S.)