An improved low-background cooled FET assembly for germanium spectroscopy

An improved low-background cooled FET assembly for germanium spectroscopy has been designed and tested at PNNL. This assembly was designed to improve signal fidelity, improve physical reliability under thermal cycling, and optimize the temperature of the FET. While meeting these goals, the assembly must also contribute negligibly to the radioactive background of the detector system. Component and material screening for this system were accomplished with two different PNNL ultra-low level spectrometers. Thermal design was validated using a cold stage at a variety of temperatures. Its temperature dependence allowed us, in one case, to calibrate the resistive feedback element as a temperature sensor. Electronic response was measured and compared to existing low-background and commercial systems. The result is an electrical and physical package that is robust and useful for special applications such as pulse shape analysis and ultra-low background radiation detection.