Purpose of the flight and payload description
The objective of the flight was to study the spectrum of gamma rays of strictly atmospheric origin using a balloon-borne instrument operated at a geomagnetic cutoff rigidity of 12 GV. The experiment was developed by the Instituto de Pesquisas Espaciais (INPE), an organization of the Conselho Nacional de Pesquisas within the Brazilian Federal Public Service, headquartered in São José dos Campos, São Paulo, Brazil.
The instrument, shown schematically in the image at left, was an omnidirectional scintillation detector. Its primary sensing element was a cylindrical sodium iodide crystal activated with thallium, NaI(Tl), measuring 10.16 cm in diameter and 10.16 cm in height. The crystal was optically coupled directly to an RCA 8055 photomultiplier tube. At the time, NaI(Tl) was the most widely used scintillation material for gamma-ray measurements aboard stratospheric balloons because of its high detection efficiency, provided it was adequately protected against moisture and mechanical shock.
The NaI(Tl) crystal was surrounded by a secondary scintillator consisting of an NE-102A plastic scintillator operating as an anti-coincidence shield. This detector was coupled to an RTC XP 1030 photomultiplier tube and served to reject charged-particle events that interacted within the instrument. The plastic scintillator vetoed charged particles with energies greater than approximately 700 keV, while the NaI(Tl) detector measured gamma rays in the 0.918 MeV energy range.
Electrical pulses generated by the RCA 8055 photomultiplier were amplified and processed by a 128-channel pulse-height analyzer. Signals from the RTC XP 1030 photomultiplier were routed to an anti-coincidence circuit. Pulse-height analysis was performed only when no signal was present in the anti-coincidence channel, thereby eliminating events produced by charged particles and ensuring that the recorded spectrum corresponded exclusively to gamma-ray interactions. Because no practical Collimated detection systems existed at that time for this energy range, the detector was designed to accept radiation from all directions and was therefore classified as omnidirectional.
During flight, both scientific and housekeeping data were transmitted through an FM/FM telemetry system operating at a center frequency of 137 MHz. Housekeeping measurements were managed by a nine-channel commutator that sequentially monitored the principal supply voltages, the temperatures inside and outside the detector housing, and the ambient atmospheric pressure.
Details of the balloon flight
Balloon launched on: 10/20/1973 at 7:12 UTC
Launch site: National Institute of Space Research, Sao Jose dos Campos, Sao Paulo, Brazil
Balloon launched by: Instituto Nacional de Pesquisas Espaciais (INPE)
Balloon manufacturer/size/composition: Zero Pressure Balloon model 25SV5 53.000 m3
End of flight (L for landing time, W for last contact, otherwise termination time): 10/20/1973 at L+10
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 10 h
Landing site: In Andrelandia, Minas Gerais, Brasil
Payload weight: 65.7 kgs
The balloon was launched from INPE, in São José dos Campos, at 7:12 UTC on 20 October 1973. It reached its ceiling altitude of 3.5 mb at 9:00 UTC, and continued flying until 19:54 UTC, remaining at a float level between 3.5 and 6 mb for the duration of the flight. Gamma-ray and charged-particle count rates were recorded as functions of time and pressure, showing the Pfötzer maximum near 120 mb. This was the second flight of the instrument. During this second flight readings showed an increase in gamma-ray and charged-particle count rates relative to previous flight, attributable to a geomagnetic disturbance that affected the data collected between roughly 100 mb and the float ceiling, between about 8:00 UTC and 11:00 UTC. Spectra were obtained for several pressure intervals during ascent and at float, including the ranges 360200 mb (sampling time of 10 minutes) and 12590 mb (sampling time of 5 minutes), as well as spectra near the ceiling of 3.5 mb measured at pressures of 4.5 mb (sampling time of 32 minutes) and 4.3 mb (sampling time of 30 minutes), the latter representing a calm (undisturbed) period following the geomagnetic disturbance, while a separate spectrum at 3.5 mb during the disturbed period showed a notably softer spectral index (around 1.5) compared to the calm-period spectrum (around 1.0) in the 0.9-2 MeV energy range, clearly demonstrating the influence of the magnetic disturbance on the locally measured gamma-ray spectrum.
External references
- Determinacao do espectro de raios gama produzidos na atmosfera pelos raios cósmicos primários Sao Jose dos Campos: INPE, 1975. 96 p. Relatório preparado como parte dos requisitos necessários à obtenção do Título de Mestre em Ciência Espacial
If you consider this website interesting or useful, you can help me to keep it up and running with a small donation to cover the operational costs. Just the equivalent of the price of a cup of coffee helps a lot.
