An improved array of microcalorimeters has been devised for use as photon detectors in an x-ray spectrometer for astrophysical research. The spectrometer will be used to measure the spectra of celestial objects in the "soft" x-ray range (photon energies from 200 eV to 10 keV), to a resolution much higher than has been possible until now.

Microcalorimetry is an established technique for measuring x-ray energies. Each microcalorimeter includes a small mass that absorbs incident photons. The temperature of the mass rises in proportion to the energy of each absorbed photon. The temperature rise is measured to determine the energy flux of incident photons.

The Improved Array Intercepts More Photons (even when the circular image is slightly off center) than does the bilinear array.

Previous photon-detector designs for this instrument specified, variously, a linear or bilinear array of microcalorimeters. A linear or bilinear array is a long, narrow array that is not well matched to the circular image produced by an x-ray telescope: When the circular image is wider than the array and/or when the image is displaced widthwise, a significant number of incoming photons fail to strike the array. Inasmuch as astronomical photon fluxes are very low at the outset, any such loss of photons significantly degrades the performance of the instrument.

The improved array is a six-by-six square array in which the corner elements are not connected. In comparison with a bilinear array (see figure), it is better matched to the circular image produced by the telescope: The array is designed so that a greater fraction of incident photons is intercepted, even when the image is slightly off center in any direction.

This work was done by Peter Shu, Sanghamitra B. Dutta, D. Brent Mott, and Harold D. Isenberg of Goddard Space Flight Center. GSC-13808