Glenn Frye

EOSCOR: A light weight, microprocessor controlled solar neutron detector

Abstract A light weight high energy neutron detector with vertical detection efficiency of 0.005 at 40 MeV and 1.4 m2 sensitive area has been developed for long duration super-pressure balloon flight observations of solar neutrons and gamma rays. It consists of two sets of four plastic scintillator hodoscopes separated by a 1 m time-of-flight path to observe n−p, C(n, p), and C(n, d) interactions. The neutrons interactions are separated from gamma ray events through TOF measurements. For a large flare, the signal from solar neutrons is expected to be an order of magnitude greater than that of the atmospheric background. The microprocessor controls the data acquisition, accumulation of histograms, and the encoding of data for the telemetry systems. A test flight of the detector was made with a zero-pressure balloon. The expected many-week duration of a super-pressure balloon flight would significantly increase the probability of observing 20–150 MeV neutrons from a medium or large flare.

50–500 MeV observations of LMC supernova 1987A

Abstract Since the discovery of the supernova outburst in the LMC in 1987, we have made two attempts (on day 55 and day 407) to measure the high energy gamma-ray flux in the range 50–500 MeV, by using a balloon borne spark chamber telescope. On day 55, no positive signal was seen from the source. A 3σ upper limit of 2.9 × 10 −5 ph cm −2 s −1 was obtained after the analysis of the spark chamber data. Preliminary analysis of the quick look data obtained in the second flight shows that the gamma-ray flux even on day 407 was less than 9 × 10 −4 ph cm −2 s −1 (3 σ ).

A GAMMA-RAY TELESCOPE WITH ARC MINUTE RESOLUTION

A prototype imaging telescope of a kind that could be used in a future γ-ray astronomy mission has been tested using a quasi-point source of 20 MeV γ radiation. The results have demonstrated the ability to reconstruct images of the source at various positions within the field of view of the telescope. The point-spread function of the telescope was improved by nearly two orders of magnitude over that of a track chamber alone through the use of a coded aperture mask. This work has demonstrated for the first time the possibility of achieving arc minute source location with future γ-ray space telescopes. This would enable point-like γ-ray sources to be located with that precision while extended objects could be mapped with a resolution of about 10 arc min.

Spark chamber and time-of-flight detector for 15-150 MeV neutrons from an extended source

Abstract A new detection method for 15–150 MeV neutrons from an extended source utilizes a spark chamber time-of-flight technique. Both secondary particles in an n-p scatter are measured - the recoil proton in a spark chamber and the scattered neutron in a time-of-flight hodoscope, enabling the direction and energy of the incident neutron to be determined uniquely. Carbon events in the CH 2 radiator are separated from n-p scatters by the 90° kinamatical rewquirement between the secondary particles. The detection efficiency is 1x10 −4 at 70 MeV, the acceptance cone 40°, the angular resolution 3.0° and the energy resolution 10%. The detector has been used on high altitude ballon flights to measure the flux of atmospheric neutrons and to search for solar neutrons.

Hard X-ray spectrum of Supernova 1987A on day 407

Evidence for a hard X-ray continuum emission from a source in the LMC region centered on the optical position of SN 1987A is reported. The SN 1987A region was observed on day 407 with a hard X-ray and a high energy gamma-ray detector on a balloon payload. The data are compared with predictions expected from theoretical models based on the Comptonization of the Co-56 nuclear lines or the presence of an internal continuum power source. 29 refs.

Power considerations for long duration balloon flights

Abstract A solar panel, silicad battery power supply system is described which provided 100 W of power for a balloon borne solar neutron experiment. The system operated successfully on a 22 day circum-global RACOON flight launched from Australia in January 1983.

EOSCOR III, a High Energy Solar Neutron Detector

A light weight high energy neutron detector has been developed for the observation of 20-150 MeV solar flare neutrons on a long duration Sky Anchor balloon flight. It consists of two 1 m2 plastic scintillators separated by a 1 m time-of-flight path to detect the protons from n-p scattering and 12C(n, pX) interactions in the upper scintillator. Adiabatic isochronous light pipes view the scintillators. Time-of-flight and pulse height analysis are used to measure the proton velocity, to discriminate against albedo events, and to separate the slower moving protons from Compton electrons. The Monte Carlo efficiency calculations are compared with accelerator calibration results using mono-energetic neutrons. Some results from short duration high altitude balloon observations are presented.

An imaging telescope for high energy gamma-ray astronomy

Abstract Recent tests of a γ-ray imaging telescope, which incorporated a coded aperture mask and multi-wire proportional counter system produced good images of a tritium target source which was used to generate the 20 MeV protons at a proton Van de Graaff accelerator. This paper indicates what performance one might expect if a large area drift chamber were used in conjunction with a coded aperture mask. The prospects for achieving significant scientific results if such a system were flown on a variety of space vehicles are discussed.

50–500 MeV γ‐ray emission in the early phase of SN1987A

SN1987A was observed on 19th April 1987 with a combined high energy γ‐ray and hard x‐ray payload, flown on a stratospheric balloon from Alice Springs, Australia. The γ‐ray detector, sensitive in the energy range 50–500 MeV, was an optical spark chamber with 400cm2 area, a field of view of 60° FWHM and a time resolution of 10 μs. The counting rate profile at ∼2.2 mb float altitude has lead to a 3σ upper limit to the steady γ‐ray flux of 7×10−4 ph cm−2 s−1 in the 50–500 MeV range. This upper limit is compared to our predictions for the time profile of γ‐ray emission from SN1987A resulting from pulsar acceleration of particles to cosmic ray energies.

SN 1987A - The impact of greater than 50 MeV gamma-ray luminosity limits on theories of particle acceleration

Analysis of the data obtained from two flights of a balloonborne gamma-ray detector to observe SN 1987A was completed. The detector, which included a spark chamber to determine the arrival directions of the photons, was sensitive in the energy range 50-500 MeV. The 95 percent confidence upper limit to the flux on day 55 after the explosion has been established to be 1.1 x 10 exp -5 photons/sq cm/s and on day 407 to be 3.4 x 10 exp -5 photons/sq cm/s. These limits are compared with various theoretical predictions.