Eight-Channel TES Microcalorimeter System for Detector and Source Development

Nuclear forensics and environmental monitoring require rapid isotopic analysis of trace samples that contain multiple radioisotopes with closely spaced alpha particle energies. Conventional measurement of such a sample typically requires expensive and time-consuming radiochemical separations, measurement of multiple subsamples by silicon alpha spectrometry, and destructive analysis by mass spectrometry. The superior energy resolution of microcalorimeter detectors allows isotopic analysis with a single nonconsumptive alpha spectrometry measurement. In order to bring microcalorimeter alpha detector technology towards the goal of a practical analytical instrument, we have developed an eight-channel transition-edge sensor microcalorimeter system to enable rapid detector and source development. This system is now fully functional, and has enabled the identification of instabilities in our alpha detector response that resulted in degraded performance. A redesigned set of detectors has been fabricated and tested, and has shown significantly improved response. With the improved detectors, we have been able to consistently achieve energy resolution of less than 1 keV full width at half maximum at 5.3 MeV. We have prepared electroplated sources that contain 239-Pu and 240-Pu, demonstrated the ability to resolve their ~ 5.1 MeV alpha energy peaks with 0.74 keV FWHM resolution, and shown that the 240/239-Pu isotopic ratios obtained from our microcalorimeter spectra are in statistical agreement with mass spectrometry results.