Showing papers by "Gordon P. Garmire published in 1995"

Soft X-ray spectroscopy with sub-electron readnoise charge-coupled devices

Abstract: We demonstrate use of a charge-coupled device (CCD) with sub-electron readnoise performance as a non-dispersive X-ray spectrometer. The exceptionally low readnoise (0.9 electrons rms) was achieved by applying a floating gate output amplifier with 16 readouts per pixel. The soft X-ray quantum efficiency was enhanced over other front-side illuminated devices by using a novel thin-poly gate structure. The combination of sub-electron noise and good soft X-ray quantum efficiency have enabled us to detect photons in the EUV energy range (E

Measuring the soft X-ray quantum efficiency of charge-coupled devices using continuum synchrotron radiation

Abstract: We have measured the soft X-ray (250–4500 eV) quantum efficiency of a charge-coupled device using continuum synchrotron radiation. The spectrum of the synchrotron radiation can be calculated accurately, so the observed pulse height spectrum is a direct measure of the detector efficiency over the synchrotron bandpass. A key function in modeling the efficiency is the energy dependence of the fraction of detected single pixel events. We find that a model including the effects of charge drift and diffusion plus two different depletion depths (corresponding to the collection and barrier phases under the gates) is required. With this model the absolute QE can be determined to within ∼5% everywhere over the 500 to 4500 eV bandpass.

CUBIC: x-ray CCD spectroscopy of the diffuse x-ray background

Abstract: The cosmic unresolved background instrument using CCDs (CUBIC) is currently scheduled for launch on the Argentine/US SAC-B satellite late this year. This instrument is designed to perform moderate resolution nondispersive x-ray spectroscopy of the diffuse x-ray background over the band 0.2 - 10.0 keV using state-of-the-art photon-counting CCDs. The instrument is optimized for spectroscopy of diffuse emission with a field of view of 5 degrees by 5 degrees below 1 keV and 10 degrees by 10 degrees above 3 keV. Observations will typically last 1 - 3 days, and will obtain high quality CCD spectra of the diffuse background, nearby superbubbles and supernova remnants, and the brightest x-ray point sources. This paper gives an overview of the instrument design and CCD detectors.

CUBIC: preflight calibration status

Abstract: CUBIC, the cosmic unresolved x ray background instrument using CCDs, is instrumented to make moderate resolution x-ray spectral measurements of diffuse targets at spatial scales of a few degrees. While the energy range is nominally 200 eV - 10 keV, the CCDs have been designed to maximize the soft x ray performance by using novel structures. A two part aperture increases the area-solid angle product above 1 keV to maximize sensitivity to the cosmic component of the diffuse x ray background. Here we report preliminary results of our preflight laboratory calibrations performed at Penn State of the dark current, readnoise, nonlinearity, charge transfer efficiency, energy resolution, and quantum efficiency of the two flight CCDs. We also discuss calibration of the detector field of view and the preliminary area-solid angle product of the instrument.

CCD x-ray detectors: on-board data processing

Abstract: We present the results of a comparison of data processing algorithms to be used with space- borne x-ray CCD cameras such as those aboard ASCA, CUBIC and AXAF The goal is to optimize efficiency and accuracy based upon the capabilities and limitations of the on-board processors We examine the two main components of processing: determination of the bias (or zero) -level, and event recognition An algorithm to generate a pixel-by-pixel bias by on-board processing is developed and tested The on-board bias frame is compared to a bias created from a standard laboratory pixel-by-pixel averaging of dark frames We show that an accurate pixel-by-pixel bias frame can be created with an on-board algorithm in as few as 15 frames We show that a bias frame created from that algorithm performs as well as meanframes created in the laboratory On-board algorithms that handle bias determination and event selection simultaneously are also developed We show that several types of these algorithms successfully process the CCD data, although the algorithm should be chosen according to the specific capabilities of the processors The procedures were evaluated by examining event quality and single/split event ratios, and more importantly by the determination of spectral energy resolution (eg, the FWHM of 55Fe) The algorithms were compared and evaluated for laboratory data from several different cameras and types of CCD devices© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only