Microcalorimeter Nuclear Spectrometers

We present results from the initial testing of arrays of cryogenic microcalorimeter gamma-ray detectors. The successful fabrication and multiplexed operation of these arrays allow us to make pixel-to-pixel performance comparisons. The relationship between operating conditions and array performance is investigated. Advanced refrigerators for these detectors work without liquid cryogens, achieve temperatures below 100 mK, and operate continuously for many days.