Nuclear diagnostics with cryogenic spectrometers

Cryogenic spectrometers offer an energy resolution an order of magnitude higher than conventional high-purity Germanium detectors, since low-temperature operation reduces thermal fluctuations and the associated noise. They have been developed over the last several decades, initially driven by particle and astrophysics applications, more recently also for material science, biophysics and nuclear science applications. The Advanced Detector Group at LLNL is developing cryogenic Gamma-ray and fast-neutron spectrometers for nuclear diagnostics in fundamental science and national security. They are based on measuring the increase in temperature upon photon or particle absorption with a sensor operated at the transition between its superconducting and its normal state. The approach can be adapted for different types of radiation with the appropriate choice of absorber material. We describe our Gamma-ray spectrometers consisting of a bulk Sn absorber attached to a superconducting Mo/Cu multilayer sensor. The detectors are operated at a temperature of ∼0.1 K the end of a cold finger in a two-stage adiabatic demagnetization refrigerator, and have, depending on design, achieved an energy resolution between 50 and 150 eV FWHM for energies below 100 keV. Here we give an overview about cryogenic detectors for nuclear diagnostics, and discuss the application of this detector technology to the measurement of uranium enrichment.