Year
2008
Abstract
Superconducting ultra-high energy resolution Gamma-ray spectrometers can improve the accuracy of non-destructive analysis in nuclear safeguards in cases where conventional high-purity germanium detectors are affected by line overlap. The spectrometers are based on measuring the temperature increase upon Gamma absorption with a sensor operated at the transition between its superconducting and its normal state. Our Gamma-ray spectrometers employ bulk tin absorbers and superconducting Mo/Cu multilayer sensors. They can be designed for an energy resolution between 50 and 90 eV FWHM for energies below 100 keV, and high linearity to above 200 keV. For userfriendly operation by non-experts in nuclear safeguards applications, we have built a refrigerator based on a low-vibration pulse tube cryocooler and a two-stage adiabatic demagnetization stage that can cool the detectors to their operating temperature of 0.1 K at the push of a button. We are addressing the intrinsically small pixel size and slow response by building detector arrays and the associated readout electronics. We discuss the performance of the instruments in the context of nuclear safeguards. Specifically, we discuss their applicability for monitoring uranium mining activities by measuring the ratio between the uranium daughters Th-230 and Th-234 at ~60 keV, and between U-235 and the U-238 decay product Ra-226 at ~186 keV.