Evaluation of a fast current-preamplifier for use in thermal neutron detection

This paper explores the possibility of using a low-noise, fast, current-sensitive preamplifier as front-end electronics for fission chambers. Over the years, these detectors have been widely used for neutron measurements in Safeguards applications, including in Unattended Monitoring Systems (UMS), which are permanently installed in nuclear facilities to continuously measure a variety of processes throughout the nuclear fuel cycle. The charge-sensitive electronics coupled to these detectors needs to be located close to the detector itself, in order to minimize the susceptibility to the noise that would arise from the capacitance of long cables. However, these devices are liable to increased failure rates when applied to harsh environments such as high neutron and gamma fields and operation at extreme temperatures. Furthermore, performing maintenance and replacing preamplifiers under these harsh conditions, or in contamination areas, can be challenging and time consuming. The usage of fast current-sensitive preamplifiers has the potential to alleviate these issues. Thanks to their high tolerance to input capacitance, they can be operated with long cables and placed in less challenging environments that are more easily accessible. In addition, being by concept much faster than charge-sensitive preamplifier, current-sensitive electronics can help when high count rates need to be measured, such as in spent fuel applications. The paper will focus on the counting performance for different cable lengths of a current-sensitive preamplifier coupled to a fission chamber, investigating possible improvements for new UMS installations.