Purpose of the flight and payload description

The objective of the flight was to study the isotopic composition of cosmic-ray nuclei. The instrument designed at the University of Chicago consisted of a set of detectors aimed at accurately measuring the charge and velocity of cosmic-ray particles.

At left we can see an scheme of the detector (click to enlarge). It included two identical plastic scintillators, labeled T1 and T3, which were responsible for charge measurement. Positioned between them was a liquid Cerenkov counter, T2, which had an effective index of refraction of 1.27. This specific index enabled precise velocity measurements, particularly for particles with energies around 1 GeV per atomic mass unit (amu). To ensure uniformity in detection response, each detector was housed within a white, high-reflectance light integration box. The light output from these detectors was captured by twelve RCA 4525 photomultiplier tubes.

A key component of the system was the multiwire proportional chamber (MWPC) hodoscope, composed of three separate chambers labeled A, B, and C. This hodoscope served to define the trajectory of particles passing through the instrument, thereby allowing for corrections to path length variations and mitigating nonuniformity effects. Additionally, it played a crucial role in distinguishing nuclear events from background noise.

The plastic scintillators, constructed from 1 g/cm² Pilot Y material, had frosted surfaces to minimize total internal reflection. The high-reflectance walls of the light integration boxes were covered with Dow beadboard, ensuring efficient light collection. The liquid Cerenkov detector consisted of a 1-inch deep container filled with Dupont Freon fluorocarbon type E-2. This liquid was confined by a 0.01-inch Mylar lid, which was held taut and supported by four symmetrically placed posts that provided mechanical stability. To accommodate thermal expansion during balloon flights, a reservoir surrounded the primary liquid volume. This reservoir was sealed with a loosely fitted 0.002-inch Mylar cover, allowing for controlled volume adjustments as the temperature fluctuated by up to 30 degrees Celsius. This mechanism maintained the counter's nominal thickness, thereby stabilizing its light output.

The MWPC hodoscope consisted of an x and a y grid, each containing 64 wires positioned between high-voltage planes made of stretched Mylar coated with conductive Aqua-Dag paint. Every wire was equipped with an individual amplifier and discriminator, which registeed a firing event whenever a particle passed through. A maximum of six wires per plane could be recorded per event, with an "excess" indicator flagging instances where more than six wires were triggered. The chambers were continuously supplied with a low-flow mixture of 80% argon and 20% carbon dioxide. The pulse heights recorded in T1, T2, and T3 were processed using 2000-channel linear pulse-height analyzers.

A guard counter, labeled G, was included to help eliminate background signals originating from secondary interactions in the atmosphere. This counter was a plastic scintillator (NE 110) shaped as an annulus, and its pulse height was recorded for every event. High-energy background events or side showers typically produced significantly larger signals in the guard counter, enabling their exclusion during data analysis.

Details of the balloon flight

Balloon launched on: 9/29/1973
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 - 591.825 m3 (17.78 microns - Stratofilm)
Flight identification number: 782P
End of flight (L for landing time, W for last contact, otherwise termination time): ??/??/1973
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): F 40 h 10 m
Payload weight: 1459 kgs

External references

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