GISBE - IONIZATION SPECTROMETER

The objective of the flight was to determine the chemical composition of very high energy cosmic rays up to and beyond 100 GeV/nucleon. The instrument built around a ionization spectrometer was developed by the Max-Planck-Institut fur Physik und Astrophysik from Germany.

A schematic cross section drawing of the apparatus is shown at left (click to enlarge). It was composed basically of three parts: (a) the ionization spectrometer, for determination of the energy of incident particles; (b) a five-gap spark chamber for trajectory determination; and (c) a Cherenkov counter and a scintillation counter for charge determination of incident particles. In the image at right can be seen the apparatus without the vessel. The sensitive area of the apparatus was 1 m x 1 m. The total geometric depth was 0.60 m, providing a total geometric factor of 1.01 m2 steradian (sr).

An incident particle traversed first the Cherenkov counter and then the top scintillation counter. Both yielded signals were roughly proportional to the square of the charge Z of the incident relativistic particle, and a correlation between both signals helped to remove background events. Then the trajectory of the incident particle was observed in five planes of digitized spark chamber. Finally many of the incident particles suffered nuclear interactions in the ionization spectrometer thereby initiating particle cascades. The ionization loss of these cascades was sampled at various depths in the absorber thereby yielding an indication of the incident particle's original energy.

The ionization spectrometer consisted of 10 radiation lengths of lead interleaved with 1 cm thick plexiglass scintillators at intervals of 2 radiation lenghts (rl). On top of this there was some absorber material or "target" consisting alternatively of lead and carbon with lead on top. Each scintillator was viewed by four phototubes with a 2" photocathode. The outputs of the respective 4 phototubes of each scintillator were summed electronically and fed through linear gates to a 1024-channel pulse height analyzer each. In order to ensure proper operation and pulse height determination up to the highest possible energy of incident particles, there were mechanical shutters in front of each phototube of the lower five scintillators since there the cascades were expected to build up sizably.

Five gaps of the wire spark chamber were used for trajectory determination. The sensitive area was 1 m x 1 m and gap width 3/8". Four gaps had two wire planes with the wires at 90° with respect to each other. One gap had wire planes at 75° in order to resolve ambiguities of multi-track events. Aluminum-laminated mylar foils covered both wire planes on the outside in order to help propagating the high voltage pulse across the chamber without distortion. Readout was facilitated via a magnetostrictive wire with fiducial wires and pickup coils at both ends. The chambers were flushed continuously with 99.5% neon plus 0.5% ethane (C2H4).

On top of the spark chamber there were a plastic scintillator and a plastic Cherenkov counter. The scintillator response was maintained as uniform as possible by having the phototubes look into a white diffusion box located so that scintillation light from the edge of the scintillator was guided into this box. A baffle inside the box kept the light of the scintillator from directly propagating to the photocathodes. A box like this was placed on each of two opposite edges of the scintillator, with two phototubes looking from the top into each box. The Cherenkov counter consisted of a 3/4" x 1 m x 1 m piece of polished Pilot plastic 425 lying on the bottom of an almost dome shaped light diffusion box (the so-called "diffusor tent"). This, as well as the diffusion boxes of the charge scintillator were coated on the inside with a paint based on barium sulfate with some binder. Incident particles from above produced Cherenkov light that was reflected off the bottom of the radiator or the diffusor tent and then again reflected off the dome.

The whole apparatus was placed inside a pressure vessel, the egglike shape of which is indicated in the scheme. The vessel was wrapped with a layer of Ethafoam 4" thick for insulation and mounted in an aluminum frame for protection at impact after the flight. The total weight including batteries during the flight was about 2100 kg.

Balloon launched on: 10/12/1972
Launch site: Columbia Scientific Balloon Facility, Palestine, Texas, US  
Balloon launched by: National Scientific Balloon Facility (NSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon Winzen - 559.544 m3 (25.40 microns 2 Caps. 38.10 microns - Stratofilm)
Balloon serial number: 1.0 NS - Two 1.5 Caps Serial Number: 1
Flight identification number: 714P
End of flight (L for landing time, W for last contact, otherwise termination time): 10/13/1972
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): F 14 h
Landing site: Parachute failure. Payload destroyed
Payload weight: 2792 kgs

The balloon was launched from the National Scientific Balloon Facility base in Palestine, Texas on October 12, 1972. After a nominal ascent the balloon reached an altitude of 112.000 feet and remained in flight for 14 hours. The next day, the mission was terminated but the payload was destroyed when the parachute failed to function properly after separation from the balloon. Careful post flight analysis revealed that in the process of deployment, the parachute's canopy passed through its shroud lines causing the parachute to fail. The analysis further confirmed that the parachute was within design limits for the payload weight carried.

• A balloon-borne ionization spectrometer with very large aperture for the detection of high energy cosmic rays Nuclear Instruments and Methods, vol. 124, 1975, p. 461-476
• Cosmic Ray Composition Measurements at High Energies 13th International Conference on Cosmic Rays, Denver, Colorado, Volume 1., p.208
• Ladungszusammensetzung der kosmischen Strahlung zwischen 5 und 100 GeV/Nukleon Mitteilungen der Astronomischen Gesellschaft, Vol. 35, p.204
• National Scientific Balloon Facility Annual Report FY 1973 National Center for Atmospheric Research, September 1973
• Results on the cosmic ray chemical composition at energies up to 100 GeV/nucl Astronomy and Astrophysics, vol. 46, no. 1, Jan. 1976, p. 49-59