A.C. Rester

Compton continuum suppression by digital pulse shape analysis part II

Abstract We present results about Compton continuum suppression via pulse shape analysis using rise-time-fall-time functions or direct pulse comparison to an “optimal pulse” template which improved the local peak-to-Compton ratio by a factor of more than 5.

Performance of bismuth germanate active shielding on a balloon flight over Antarctica

The GRAD (Gamma-Ray Advanced Detector) gamma-ray spectrometer was flown on a high-altitude balloon at an altitude of 36.6 km over Antarctica on January 8-10, 1988 where it was used to make observations of Supernova 1987A. The performance of the bismuth germanate (BGO) active shielding in the near-space environment over Antarctica is examined. The promised effectiveness of this shielding in the suppression of unwanted background has been demonstrated. The BGO-shielded GRAS spectrometer detected gamma-ray lines with fluxes of 2*10/sup -3/ cm/sup -2/ s/sup -1/ from SN 1987A in a radiation background approximately a factor of 4 more intense that over Alice Springs, Australia. This level of sensitivity indicates that BGO is at least as effective as CsI when used as active shielding. Isomerism is common, both in the bismuth and germanium regions of the nuclear chart, but is found to be less of a problem for background suppression in the latter region than in the former. >

The GRAD Gamma Ray Spectrometer

A gamma-ray spectrometer for an upcoming space shuttle mission is described. Consisting of a 150 cm3 n-type germanium detector set inside active shielding of bismuth germanate and plastic scintillator, the instrument will be used in studies of the Orbiter background and the galactic center.

Neutron, proton and gamma-ray event identification with a HPGe detector through pulse shape analysis

The authors report on a series of preliminary experiments performed to investigate the current pulse shapes produced by gamma-ray, neutron, and proton interactions in a high-purity germanium (HPGe) detector. The pulse shapes are characterized on the basis of their time-to-peak (leading) and time-from-peak (trailing) edges. Each particle type generates a distinct range of current pulse shapes; this information can be used on a pulse-by-pulse basis to indicate which particle interacted in the detector. There is also an indication that current pulse shape information can be used to reduce the Compton background, which generally contributes to the background of any gamma-ray spectrum, by placing timing cuts on the leading and trailing edges of the current pulses. >

Compton continuum suppression by analog pulse shape analysis

Abstract We present experimental results on Compton continuum suppression and Compton edge flattening by analog pulse shape analysis. The local peak-to-Compton ratio was increased by a factor of 1.7.

Activation of BGO crystals with 1.5 GeV protons

A cyclindrical bismuth germanate (BGO) detector (7.5 cm diameter × 7.5 cm long) and a cylindrical bare crystal of BGO (2.5 cm diameter × 2.5 cm long) were exposed to a fluence of 1.1 × 108 protons cm−2 at 1.5 GeV energy, roughly equivalent to that expected on an interplanetary journey to Mars. No degradation in the energy resolution or counting efficiency of the BGO detector was observed, although the background continuum increased significantly. Events emanating from the bare crystal were counted externally with a high-resolution germanium detector. The activation lines identified were compared to a spectrum from an externally counted BGO detector taken on a high-altitude balloon flight over Antarctica.

Compton continuum suppression by digital pulse shape analysis

Abstract We present experimental results on a technique for flattening the Compton edges and suppressing the Compton continuum in gamma ray spectra with digital pulse shape analysis. The peak-to-Compton ratio can be improved by more than a factor 2.

The Grad Data Acquisition and Control System

A reliable, low-cost microprocessor based electronics package has been designed and built to support the Gamma Ray Advanced Detector which is scheduled to fly on the Space Shuttle in 1986. The electronics package provides for both control and data acquisition through a telemetry interface to the Air Force AFP-675 experiment support structure. By changing out two interface modules the electronics package can be reconfigured to support a variety of instruments and S/V interfaces.

Compton continuum suppression by pulse shape analysis

The authors present experimental results on suppressing and flattening the Compton continuum by digital and analog pulse shape analysis. A doubling of the Cs-peak-to-Co-Compton ratio and a nice flattening of the Compton edges were achieved by pulse shape analysis in rejecting pulses from the peripheral regions of the Ge-detector, where the Compton scattering followed by the gamma escaping from the detector is most common. The pulse shape analysis technique may also offer a way to construct a position-sensitive Ge-detector.<<ETX>>

JIGSAW: a gamma ray data acquisition, display and analysis program

The authors report on work performed to date on JIGSAW, a self-contained data acquisition, display and analysis system designed to collect data from multiple gamma-ray detectors. The data acquisition system utilizes commercially available VMEbus and NIM hardware modules and the VME exec real-time operating system. A Unix-based software package, written in ANSI standard C and with X11 graphics routines, allows the user to view the acquired spectra. Analysis of the histograms can be performed in background during the run with the ROBFIT suite of curve-fitting routines.<<ETX>>