Cryogenic Decay Energy Spectrometry

Cryogenic detectors provide some of the highest energy resolution spectra available, due to their intrinsic low thermal noise. The NIST cryogenic decay energy spectrometry facility consists of a dilution refrigerator which cools Transition Edge Sensors (TES) to below 0.05 K. Superconducting Quantum Interference Device (SQUID) amplifiers are used to enable room-temperature electronics to read miniscule changes in TES temperature. Each radioactive decay in an absorber placed in thermal contact with the TES generates pulses of heat, whose amplitude is proportional to the absorbed energy (a typical value is 1 pJ per decay). A decay energy spectrum built up from these pulses provides a unique “fingerprint” for each radionuclide in the absorber. Along with carefully designed gravimetric deposition procedures to fabricate the absorber, this technique is used in the True Becquerel project.