Development and Test of a Diamond-Based Fast Neutron Detector for 200 °C Operation

Recent improvements in the production of artificial single-crystal diamonds have made it possible to produce commercial radiation detectors. However, the availability of diamond detectors for high-temperature and high-shock applications is limited. We have developed a compact solid-state diamond detector for high-temperature applications which require compact size, stable performance, and extreme ruggedness. It is used as a fast neutron detector for monitoring the output of a pulsed neutron generator in oil well-logging tools. The sensor consists of a high-purity monocrystalline diamond wafer with metallized electrodes on both faces. One of the metallized surfaces is mounted on a metallic plate resting on a ceramic substrate. The metallized diamond assembly is mounted in a TO-257 metal housing, which has pins connected to the two electrodes on the two faces of the diamond. The detector package, consisting of the diamond sensor and the electronics assembly, has been qualified for operation in the harsh downhole environment of oil fields. This includes high temperature and repeated shocks and vibration. Units have been tested for up to 150 h at 200 °C with no degradation in signal or count rate accuracy. The count rate accuracy with a simple detection threshold regulation scheme can reach ±1% over the range from 25 °C to 200 °C. However, this detector has applications beyond well logging, wherever there is a need for a compact, reliable detector for fast neutrons in an environment where ruggedness, exposure to high temperature, compactness, and radiation hardness are essential.