C.P. Cork

Amorphous Ge bipolar blocking contacts on Ge detectors

The authors report on the performance of high-purity Ge radiation detectors with amorphous Ge (a-Ge) contacts fabricated using RF sputtering techniques. Electrical contacts formed using sputtered a-Ge films on high-purity Ge crystals were found to exhibit good blocking behavior in both polarities with low leakage currents. The a-Ge contacts have thin dead layers associated with them and can be used in place of lithium-diffused, ion-implanted or Schottky barrier contacts on Ge radiation detectors. Multielectrode detectors can be fabricated with very simple processing steps using these contacts.<<ETX>>

Long-term radiation damage to a spaceborne germanium spectrometer

Abstract The Transient Gamma-Ray Spectrometer aboard the Wind spacecraft in deep space has observed gamma-ray bursts and solar events for four years. The germanium detector in the instrument has gradually deteriorated from exposure to the ≈10 8 p / cm 2 / yr (>100 MeV ) cosmic-ray flux. Low-energy tailing and loss of efficiency, attributed to hole trapping and conversion of the germanium from n- to p-type as a result of crystal damage, were observed. Raising the detector bias voltage ameliorated both difficulties and restored the spectrometer to working operation. Together, these observations extend our understanding of the effects of radiation damage to include the previously unsuccessfully studied regime of long-term operation in space.

Temperature sensitivity of surface channel effects on high-purity germanium detectors

The temperature sensitivity of surface channel effects on planar high-purity germanium detectors was measured using 60-keV gamma-ray scanning techniques, as part of a radiation damage study. When measured in this manner, the surface effects on most detectors showed extreme temperature sensitivity in the 72–95 K region. The effect of the surface channel increased with increasing temperature to such an extent that the efficiency, as measured by the count rate in the 1332-keV peak from a 60Co source, decreased by a factor of over two in some cases. Since the peak efficiency for the 1332-keV gamma ray decreased as the temperature increased throughout the operating range (72–120 K) the effect of the surface channel must continue to increase beyond the temperature (95 K) at which the 60-keV scan loses its sensitivity because of the strong attenuation of these much lower energy gamma rays. Radiation damage had no measurable effect on the surface characteristics. No correlation between the surface effects and the resolution changes of the 1332-keV peak was observed.

The Transient Gamma-Ray Spectrometer

The authors describe the Transient Gamma-Ray Spectrometer (TGRS) to be flown onboard the WIND spacecraft. This instrument is designed to detect cosmic gamma -ray bursts over the energy range of 20 keV to 10 MeV with an expected spectroscopic resolution of 2 keV at 1 MeV (E/ Delta E=500). The active detection element is a 215-cm/sup 3 /high-purity n-type Ge crystal cooled to cryogenic temperatures by a passive radiative cooler. The geometric field of view (FOV) defined by the cooler is 170 degrees FWFM. Burst data are stored directly in an onboard 2.75-Mb burst memory with an absolute timing accuracy of +or-1.5 ms. This capacity is sufficient to store the entire spectral data set of all but the largest burst. In addition to burst measurements, the instrument will also study solar flares, search for possible diffuse background lines, and monitor the 511-keV positron annihilation radiation from the galactic center. The experiment is scheduled to be launched on a Delta II launch vehicle from Cape Canaveral on December 31, 1992. >

First-generation hybrid compact Compton imager

At Lawrence Livermore National Laboratory, we are pursuing the development of a gamma-ray imaging system using the Compton effect. We have built our first generation hybrid Compton imaging system, and we have conducted initial calibration and image measurements using this system. In this paper, we present the details of the hybrid Compton imaging system and initial calibration and image measurements

A Germanium Orthogonal Strip Detector System for Gamma‐Ray Imaging

A coded aperture, germanium‐detector based gamma‐ray imaging system has been designed, fabricated, and tested. The detector, cryostat, and signal processing electronics are discussed in this paper. The latest version orthogonal strip planar detector is 11‐millimeters thick, having 38×38 strips of 2‐millimeter pitch. The planar detector was fabricated using amorphous germanium contacts. The strips on each face of the detector lie in a chorded‐circular pattern to more efficiently utilize the area of the 10‐cm diameter germanium crystal. The detector is held in a mount that allows convenient installation and removal of the detector, lending itself to eventual tiling of such detectors into large arrays. The cryostat includes provisions to install a large volume coaxial germanium detector immediately behind the planar detector in the same cryostat. Many gamma rays Compton scatter from the planar detector into the coaxial detector. The energies of these coincident interactions are summed to increase the gamma‐r...

A 16 × 16 pixel array detector for protein crystallography

Abstract A 2D pixel array detector prototype is being designed for static and time resolved protein crystallography. This pixel detector will significantly enhance time resolved laue protein crystallography by two or three orders of magnitude compared to existing sensors such as films or phosphor screens coupled to CCDs. The resolution in time and dynamic range of this type of detector will allow to study structural changes that occur within the protein as a function of time (concurrent readout and acquisition). The prototype consists of an array of 16 × 16 pixels of 150 × 150 μ m 2 size. The individual pixel processor consists of a low-noise amplifier shaper followed by a differential threshold comparator which provides the counting of individual photons with energies above a programmable threshold. To accommodate the very high rates, above 5 × 10 8 /cm 2 /s, each pixel processor has a 3 bit pre-scaler which divides the event rate by 8. Overflow from the divider which defines a pseudo fourth bit will generate a readout sequence providing the pixel address. Addresses, generated locally as quantified analog signals, will be used to increment a location in an histogramming memory from which the computerized image of the Laue diagram will be generated.

A High Resolution Gamma-ray and Hard X-ray Spectrometer (HIREGS) for Long Duration Balloon Flights

Abstract The HIREGS gamma-ray spectrometer made a 23-day Long Duration Balloon Flight (LDBF) from Antarctica in January 1995 to observe Galactic sources of gamma-ray and hard X-ray line and continuum emission. The scientific instrument itself is discussed, followed by a more extensive discussion of the characteristics of the instrument unique to LDBFs. The flight performance and preliminary results are briefly summarized.

A prototype 8 × 8 pixel array X-ray detector for protein crystallography

Abstract An 8 × 8 pixel array X-ray detector prototype ( 1 100 maximum is less than 1 pixel width (150 μm), which is less than ( 1 2 ) that of a CCD and ( 1 7 ) that of an imaging plate detector [1].

High-resolution gamma-ray and hard x-ray spectrometer for long- duration balloon flights

The elements of a high resolution gamma-ray spectrometer, developed for observations of solar flares, are described. Emphasis is given to those aspects of the system that relate to its operation on a long duration balloon platform. The performance of the system observed in its first flight, launched from McMurdo Station, Antarctica on 10 January, 1992, is discussed. Background characteristics of the antarctic balloon environment are compared with those observed in conventional mid-latitude balloon flights and the general advantages of long duration ballooning are discussed.