May 12, 1999
May Report
Resolutions of 2.38 eV FWHM measured at 1.5 keV and 4.7 eV FWHM measured at 5.9 keV with Mo/Cu TES at NIST
Two Mo/Cu TES devices made at NIST-Boulder, one optimized for soft X-rays and the other for 6 keV, have produced significant improvements in energy resolution. The soft X-ray device demonstrated a resolution of 2.38 eV FWHM at 1.5 keV (Al K-alpha fluorescence) at an incident X-ray rate of 450 counts/s. The other device demonstrated a resolution of 4.7 eV at 5.9 keV, resolving without question the Mn K-alpha lines from an Fe-55 source. Both of these results were obtained without bismuth absorbers for quick detector verification. This does not affect the soft X-ray result, because most of the X-rays are absorbed in the TES itself, but at 6 keV there are enough photons absorbed in the silicon-nitride to require subtraction of a background component. Subsequent devices with Bi absorbers are expected to provide even better spectra. These results demonstrate important strides towards the requirements of Constellation-X.
NTD Germanium Calorimeters produce a line core consistent with 4 eV FWHM resolution
We have made significant advances in understanding our NTD-based microcalorimeters. The SAO/Brown/LBL team has measured a line core consistent with a resolution of 4 eV FWHM within a broadened line at 6.4 keV with the NTD Ge and Sn calorimeter at SAO. The origin of a major source of the instrumental broadening has been discovered and its removal will enable the team to further enhance the detector performance. Results of preliminary steps to eliminate the effects of this additional noise source suggest an improvement in the energy resolution from 7 eV at 5.9 keV to 4 eV at 6.4 keV. The SAO/Brown/LBL team is part of the Microcalorimeter Integrated Product Team.
SXT development team at MSFC successfully electroforms and separates 0.5 m pathfinder shells with 1/2, 1/3 the weight of XMM Optics
MSFC has made two 0.5 meter diameter replicated shell pathfinder optics as part of their SXT process development activity. The shells do not yet have good optical performance, but they verify the replication and plating process and so this accomplishment is very significant. Both shells are made from a high-performance nickel alloy developed by MSFC that makes light weight shells possible. The first has a weight that would produce a mirror assembly with one-half the weight of the XMM mirror. The second would produce a mirror assembly with one-third that of XMM. Thinner shells require integral stiffening. MSFC is about to begin development for this.
New estimates of radiation background in the hard X-ray detectors
The team led by T. Armstrong, B. Colborn (SAIC), and B. Ramsey (NASA/MSFC) have estimated the background induced by space radiation in the HXT focal-plane detector. For a preliminary assembly design placed in an L2 orbit, the diffuse X-ray background dominates below 20 keV while counts from the activation of the BGO active shield/collimator dominate at higher energies. The background at L2 is currently estimated to be 4 to 6 times lower above 20 keV than the corresponding background if the satellite were placed in a low Earth orbit. The background simulations suggest approaches for detector modifications that may provide further background reduction at L2.
