Purpose of the flight and payload description
The Multistage Ionization and Cerenkov System was a prototype of a balloon-borne cosmic ray detector developed by researchers at the University of Tokyo's Institute for Cosmic Ray Research, the National Laboratory for High Energy Physics, Yamagata University, and Kobe University. It was designed to observe the chemical composition and energy spectra of cosmic ray particles with atomic charges between Z=6 and Z=30 in the energy range of 4 to 200 GeV per nucleon, as well as to measure the mean isotopic composition near the geomagnetic cutoff of 10 GV.
In the image at left we can see an schematic drawing of MICS (click to enlarge). The instrument was built around three main detector subsystems stacked in a layered configuration. The first consisted of two diffusion-type Cherenkov detectors with different refractive indices, referred to collectively as CRD. The lower Cherenkov radiator (CRDB) was a solid acrylic plate of 50 cm diameter and 2 cm thickness. The upper Cherenkov radiator (CRDA) used a liquid medium contained in an aluminum vessel of 50 cm diameter and 1.5 cm depth with a 190 micrometers thick teflon window. Each radiator was enclosed in a white light integration box, and the Cherenkov light emitted from each was detected by four 5-inch phototubes. These two Cherenkov detectors with their different refractive indices allowed charge identification across the wide Z range targeted by the experiment.
The second major subsystem consisted of five parallel plate pulse ionization chambers, designated PIC. Each chamber was composed of eleven parallel plates of 120 micrometers aluminized mylar, 50 cm in diameter, with 3.5 cm gaps between plates. The output from the five collecting electrodes of each chamber was taken separately and the pulse heights analyzed individually. The average pulse height across the five PICs (PICAV) and the standard deviation of those pulse heights were computed event by event.
The third subsystem consisted of four layers of multiwire proportional counters, designated PRC. Each layer comprised 25 multi-anode proportional counters of 50 cm diameter and 1.5 cm thickness, providing a position resolution of ±1 cm in both the X and Y coordinates for tracking the particle trajectory. The PIC and PRC subsystems were enclosed together in a pressurized container filled with a gas mixture of 95% argon and 5% methane at one atmosphere.
The prototype had a geometric factor of 1300 cm² str and a total mass of approximately 200 kg. From the results obtained during the flight test, two more instruments were developed and flown in subsequent years by the same scientific group: HEIC that scaled up the prototype to 6300 cm² str and 250 kg, keeping similar Cherenkov detectors but larger, adding a plastic scintillator, and targeting isotopic composition of heavy nuclei above 10 GV and HECRO that replaced the liquid Cherenkov with a CO2 gas detector at 0.25 atm to reach a 70 GeV/n threshold, expanded to 7300 cm² str and 300 kg, and aimed at measuring the heavy nuclei energy spectrum above that threshold.
Details of the balloon flight
Balloon launched on: 5/19/1980 at 18:28 JST
Launch site: Sanriku Balloon Center, Iwate, Japan
Balloon launched by: Institute of Space and Astronautical Science (ISAS)
Balloon manufacturer/size/composition: Zero Pressure Balloon model B50 50.000 m3
Flight identification number: B50-16
End of flight (L for landing time, W for last contact, otherwise termination time): 5/20/1980
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 32 h
External references
- Multistage Ionization and Cerenkov System Proceedings of the 17th International Cosmic Ray Conference, France. Vol 9., p.311
- Observation of Cosmic Ray Heavy Nuclei above 5 Gev/n Proceedings from the 18th International Cosmic Ray Conference, held in Bangalore, India, 22 August - 3 September, 1983. Volume 9, p.103
- Observation of Cosmic-Ray Nuclei above 5 Gev/n Proceedings of the 17th International Cosmic Ray Conference, held in Paris, France. Volume 2., p.58 A
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