An NTD germanium-based microcalorimeter with 3.1Â eV energy resolution at 6Â keV

This paper reports recent advances in our microcalorimeter spectrometer that result in an energy resolution of 3.1 eV FWHM for 6 keV X-rays. We have developed a detailed model that indicates that further minor improvements will realize 2 eV FWHM at 6 keV and well under 2 eV at 1 keV. The results demonstrate the value of the microcalorimeter for many applications where a premium exists for very fine resolution in the 0.2-10 keV energy band.