P.S. Haskins

Demonstration of three-dimensional imaging with a germanium Compton camera

A proof-of-concept experiment was performed to demonstrate the three-dimensional imaging capabilities of an all-germanium Compton camera for near-field sources. Eight high purity germanium (HPGe) coaxial detectors were configured in two planes of four detectors each. The data acquisition system was assembled from available hardware and off-the-shelf electronics using standard NIM and CAMAC modules. Sixteen-parameter data were recorded event-by-event for later analysis and image reconstruction. The energy resolution of the system was 0.3% at 1333 keV. Preliminary analysis indicates the position resolution for a source at one meter and a specific detector geometry was less than a centimeter. >

Effects of increased shielding on gamma-radiation levels within spacecraft

The Shuttle Activation Monitor (SAM) experiment was flown on the Space Shuttle Columbia (STS-28) from 8-13 August, 1989 in a 57 degrees, 300 km orbit. One objective of the SAM experiment was to determine the relative effect of different amounts of shielding on the gamma-ray backgrounds measured with similarly configured sodium iodide (NaI) and bismuth germante (BGO) detectors. To achieve this objective twenty-four hours of data were taken with each detector in the middeck of the Shuttle on the ceiling of the airlock (a high-shielding location) as well as on the sleep station wall (a low-shielding location). For the cosmic-ray induced background the results indicate an increased overall count rate in the 0.2 to 10 MeV energy range at the more highly shielded location, while in regions of trapped radiation the low shielding configuration gives higher rates at the low energy end of the spectrum.

Gamma-ray measurements from the space shuttle during a solar flare

An X2/2B level solar flare occurred on 12 August, 1989, during the last day of the flight of the Space Shuttle Columbia (STS-28). Detectors on the GOES 7 satellite observed increased X-ray fluxes at approximately 1400 GMT and a solar particle event (SPE) at approximately 1600 GMT. Measurements with the bismuth germanate (BGO) detector of the Shuttle Activation Monitor (SAM) experiment on STS-28 showed factors of two to three increases in count rates at high latitudes comparable to those seen during South Atlantic Anomaly (SAA) passages beginning at about 1100 GMT. That increased activity was observed at both north and south high latitudes in the 57 degrees, 300 kilometer orbit and continued until the detector was turned off at 1800 GMT. Measurements made earlier in the flight over the same geographic coordinates did not produce the same levels of activity. This increase in activity may not be entirely accounted for by observed geomagnetic phenomena which were not related to the solar flare.

The Shuttle activation monitor: a system for direct comparison of gamma-ray detector materials in a space environment

An experimental system which was used to compare gamma-ray detector materials in a space environment is described. Two 3-in*3-in scintillator detectors, NaI and BGO, were flown on the Space Shuttle Columbia as part of the Shuttle Activation Monitor (SAM) experiment. The goals of this experiment were to compare the performance of the two detector materials in the same environment and to measure the variations in dynamic radiation background as a function of geomagnetic coordinates, amount of shielding, and type of detector material. Twenty-four hours of data in 5-min time bins were recorded with each detector in both high-shielding and low-shielding locations in the Orbiter middeck. The high-inclination orbit (57 degrees , 160 nmi) provided exposure to the trapped charged particles in the South Atlantic Anomaly as well as the electrons in the polar regions. The system used specially adapted off-the-shelf hardware for data acquisition and storage. The multichannel analyzer was a commercially available unit with added circuitry to support an active particle shield. Data during the flight were stored using a cassette tape recorder. A preliminary look at some of the data from the first flight is included. >

Contribution of secondaries to the radiation environment on space missions

Calculations to predict the radiation environment for spacecraft in low earth orbit sometimes ignore the contribution from secondary radiation products. However, the contribution of secondaries, particularly neutrons, on heavy spacecraft or in planetary bodies can be of concern for biological systems. The Shuttle Activation Monitor (SAM) and Cosmic Radiation Effects and Activation Monitor (CREAM) experiments provide valuable data on secondary (as well as primary) radiation effects. Comparisons have been made between induced activity from flight-exposed samples, induced activity in a ground-irradiated sample, and Monte Carlo-derived predictions with and without secondaries. These comparisons show that for a flight-exposed sample, predictions which omit the secondary contribution result in a spectrum that is too low by a factor of 2. The addition of the secondaries results in a predicted spectrum that closely matches the measured data.

Performance of a BGO detector in low Earth orbit

A 7.6-cm*7.6-cm BGO (bismuth germanate) detector was flown in the middeck of the Space Shuttle Columbia August 8-13, 1989, as part of the Shuttle Activation Monitor (SAM) experiment. One of the goals of this experiment was to compare the performance of the BGO to that of NaI in the same environment. Twenty-four hours of data in 5-min time bins were recorded with each detector in each of two locations in a high-inclination orbit (57 degrees , 300 km). Pre- aid post-flight low-background counting was preformed for identification of activities induced by the space radiation environment. A number of isotopes attributed to induced activity from exposure to the space radiation environment have been tentatively identified. >

Radiation survey of the LDEF spacecraft

The authors report the first complete gamma-ray survey of a large spacecraft, the Long Duration Exposure Facility (LDEF). The survey was conducted using an array of germanium detectors from the US Naval Research Laboratory and individual detectors from the Institute for Space Science and Technology to study the accumulation and distribution of radioisotopes induced in the wide variety of materials present on the LDEF. /sup 22/Na, /sup 7/Be, /sup 54/Mn/el, and the positron annihilation line were all strongly observed. Traces of /sup 56/Co, /sup 57/Co, and /sup 60/Co were also observed The most striking feature of the data was the unexpected distribution of /sup 7/Be, which was predominately present on the leading surfaces of the spacecraft. The evidence clearly indicates an accretion of the /sup 7/Be onto the surface of the LDEF. This is the first known observation of the deposition of a radioisotope onto the surface of a spacecraft. /sup 7/Be is a spallation product of cosmic rays on nitrogen and oxygen in the upper atmosphere. To explain the surface density of 5.4*10/sup 5/ atoms/cm/sup 2/, it must be assumed that the light /sup 7/Be atom is transported up from lower altitudes. >

Activation of space-borne bismuth germanate γ-ray detectors

Results are presented from the Shuttle Activation Monitor flown in the Space Shuttle middeck area on two missions during August 1989 and September 1991. This experiment has been valuable in the study of induced radioactivity in BGO scintillators resulting from bombardment by cosmic-rays, trapped protons, and their secondaries created by interactions in a heavy spacecraft. Data from mono-energetic proton irradiation experiments have allowed investigation of activation effects in BGO for less complicated irradiation conditions, and the results from these experiments are also presented. Detailed simulations of spacecraft shielding and BGO detector activation have also been performed. The output from these compare very well to the experimental data, allowing features in the measured spectra to be identified, and the contributions from the major sources of radiation to be quantified.<<ETX>>

Induced activity in scintillation detectors in space

Abstract An experimental system was flown on the Space Shuttle Columbia from August 8 to 13, 1989 as part of the Shuttle Activation Monitor (SAM) program [P.S. Haskins et al., IEEE Trans. Nucl. Sci. NS-37 (6) (1990) 1256]. Gamma-ray spectra were collected both during flight and after landing from two 3 in. × 3 in. scintillation detectors, Nal and BGO. The shuttle was in a high inclination (57 °) orbit, at an altitude of 300 km which provided exposure to the trapped charged particles in the South Atlantic Anomaly (SAA) as well as the electrons in the Polar regions. The induced radiation observed by the detectors resulted from both external and internal sources activated by the interaction with the energetic charged particles. The flight data analysis indicates variation of the induced external radiation as a function of geomagnetic coordinates and amount of shielding, whereas the post-landing data exhibits induced internal radiation from the two different types of detector materials.

A CAMAC-based Data Acquisition System With A Macintosh Interface

A commercially available Macintosh-based data acquisition system and its application to a specific measurement is described. Based on Computer Aided Measurement and Control (CAMAC) and Nuclear Instrumentation Module (NIM) standard modules, the data acquisition system features a hardware and software interface to a Macintosh computer. This system has been used both for laboratory and remote site measurements, and has been found to perform well as both a highly interactive laboratory system and as a very automatable system for long term data acquisition. Ease in configuration allows for flexibility in fast response applications where a data acquisition system is needed in short time. The system software also supports much of the data analysis and presentation of results with a versatile set of histogram display and manipulation tools. In a recent application, the system controlled data acquisition for two germanium detectors used as part of the whole-spacecraft induced activation measurements of the Long Duration Exposure Facility (LDEF) satellite.