Modern Electronics for Safeguards Applications

Commercially available analog electronics often have shortcomings as far as safeguards applications are concerned. One particular case involves preamplifiers for detectors such as fission chambers and helium proportional counters. Current commercial units are often too sensitive to cable length, both on the input (detector side) and on the output (data acquisition side) to be useable in many safeguards applications that demand long cables. In addition, the devices have wide parameter tolerances and a lack of readout information about threshold/gain settings, which means that replacing a failed module requires extensive measurements with nuclear material or sources. Such measurements are always time-consuming and often impractical. These devices are not designed to work in a harsh outdoor environment or to tolerate a wide range of humidity and temperature. Some safeguards applications require a threshold setting just above the knee of the plateau of the high voltage (HV) characteristic in order to increase the tolerable gamma field. In this case the sensor does not benefit from the inherent gain/threshold insensitivity of the detector and will suffer significant efficiency changes with temperature and high voltage. We present the design for a universal preamplifier that can serve both fission chambers and 3He tubes and will overcome the shortcomings presented above. In addition to being less sensitive to cable length (it can tolerate meters of cable), the gain/threshold of the preamplifier can be calibrated against a desired threshold of input charge. This means that the operating point of the unit can be easily and reproducibly set to a known value and that replacement units can be set to the same value without the need for nuclear material and sources. The initial tests show significantly lower power consumption and temperature drift than commercially available instruments. We will discuss the charge calibration device and procedure for in-field replacement. Also, we will address such environmental factors as temperature and humidity and technical measures to mitigate these factors.