Detector system for monitoring fissile mass flow in liquids and gases

A computer controlled detector/electronics module has been designed and constructed for the Oak Ridge National Laboratory fissile mass flow (FMF) monitor. The FMF monitor employs a host computer, a modulated neutron source (Cf-252) and four of the gamma-ray detector/electronics modules described here to non-intrusively measure liquid or gas fissile-mass-flow rates in a pipe. The gamma-ray detector/electronics modules each consist of a bismuth germanate/photomultiplier-tube scintillation detector, an integrating preamplifier, a bipolar spectroscopy amplifier, two single channel analyzers, a temperature sensor and an on-board network communications node. The host computer automatically calibrates amplifier gain and single-channel analyzer thresholds via the network using a characteristic emission peak of the material flowing in the pipe and corrects for detector gain variations due to the temperature coefficients of the bismuth germanate. The single channel analyzer output pulses are counted by a microprocessor on board the network node and reported to the host computer. The key components of the detector/electronics module are described and initial data obtained with the FMF monitor are presented.