Purpose of the flight and payload description
The objective of the flight was to investigate the high-energy secondary cosmic radiation produced in the atmosphere by interactions between primary cosmic rays and atmospheric nuclei. The experiment focused on measuring both the neutral and charged components of secondary cosmic radiation at a location with a high geomagnetic cutoff rigidity of approximately 11.5 GV. The experiment was conducted by researchers of the Instituto de Astronomía y Física del Espacio (IAFE), Buenos Aires, Argentina.
The payload consisted of an omnidirectional scintillation detector designed to measure neutral and charged secondary cosmic radiation. Its primary detector was a 16 × 16 × 24 cm plastic scintillator sensitive to gamma rays, neutrons, electrons, protons, and muons. The detector volume provided sufficient interaction probability for high-energy gamma rays and allowed measurement of energy deposited by traversing charged particles.
The central scintillator was surrounded by a 1 cm thick plastic scintillator shield operating as an anti-coincidence detector. Events recorded only in the central scintillator were attributed primarily to neutral radiation, mainly atmospheric gamma rays, while simultaneous signals in both scintillators identified charged-particle events. This configuration enabled separation of neutral and charged radiation components.
The instrument operated in two telecommand-selectable modes. In veto-on mode, only central-detector pulses not accompanied by signals from the external scintillator were analyzed, providing gamma-ray measurements with charged-particle rejection. In veto-off mode, all events were accepted, allowing measurement of the combined neutral and charged radiation field. Charged-particle spectra were obtained by subtracting veto-on data from veto-off data.
Signal processing used a pulse-height-to-time converter that transformed pulse amplitude, proportional to deposited energy, into pulse duration. The resulting signals were recorded and later reconstructed with a multichannel analyzer. The electronics package was redesigned from earlier versions, particularly the pulse-height-to-time conversion system.
The detector measured gamma rays above approximately 4.15 MeV. Charged-particle thresholds were about 4.15 MeV for electrons, 6 MeV for muons, and 10 MeV for protons. Analysis of energy-loss spectra showed that a peak near 32 MeV observed at float altitude was produced mainly by high-energy relativistic muons crossing the detector horizontally. The detector geometry allowed identification of these events through their characteristic energy deposition over a path length of approximately 16 cm.
Telemetry transmitted pulse-height spectra together with housekeeping data, including atmospheric pressure, instrument temperatures, and counting rates from the central and anti-coincidence scintillators. All data were recorded on magnetic tape for post-flight analysis.
Details of the balloon flight
Balloon launched on: 2/24/1978
Launch site: Third Air Brigade, Reconquista, Santa Fe, Argentine
Balloon launched by: División Globos, Comisión Nacional de Investigaciones Espaciales
Balloon manufacturer/size/composition: Zero Pressure Balloon 30.000 m3
End of flight (L for landing time, W for last contact, otherwise termination time): 2/24/1978
Balloon flight duration (F: time at float only, otherwise total flight time in d:days / h:hours or m:minutes - ): 6 h
The balloon was launched from Reconquista, Santa Fe Province, Argentina, on 24 February 1978. The launch site was located in a region with a geomagnetic cutoff rigidity of approximately 11.5 GV. During ascent, the payload operated primarily in veto-off mode, collecting combined charged and neutral radiation data while passing through different atmospheric depths. The balloon climbed through the Pfotzer maximum region, where secondary cosmic-ray intensity reached its maximum. It eventually reached a float altitude corresponding to an atmospheric depth of approximately 9.5 g/cm2.
After reaching ceiling altitude, the balloon maintained float conditions for approximately five hours. During this period the instrument alternated between veto-off and veto-on operating modes. Approximately 90 minutes of data were collected with charged-particle events included, while roughly 150 minutes were devoted to measurements with the anti-coincidence veto active for gamma-ray studies. At float altitude, an atmospheric gamma-ray spectrum was obtained and compared with an earlier measurement performed in 1973, showing excellent agreement. Measurements also revealed that the gamma-ray spectral shape remained essentially unchanged between the Pfotzer maximum and the top of the atmosphere.
Analysis of charged-particle spectra collected during ascent and float led to the identification of a dominant horizontal relativistic muon component and allowed estimation of its horizontal intensity at ceiling altitude. The flight successfully achieved all major scientific objectives and provided one of the most detailed balloon-borne measurements of high-energy atmospheric gamma radiation and secondary charged cosmic radiation performed in Argentina during that period.
External references
- A Determination of the Atmospheric Gamma-Ray Spectrum between 10 and 100 MeV made at High Geomagnetic Cut-Off Revista Mexicana de Astronomia y Astrofisica, Vol. 36, p. 81-88 (2000)
- A measurement of the high energy secondary charged cosmic radiation Astrophysics and Space Science, vol. 208, no. 1, p. 125-133
- Atmospheric Gamma-Ray Spectrum Between 10-MEV and 100-MEV Astrophysics and Space Science, Volume 190, Issue 2, pp.317-329
- Una medición de la radiación cósmica secundaria neutra y cargada de alta energía Geoacta; vol. 10, no. 1, 1979, Pag. 123
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