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I.N. Azcarate (Instituto Argentino de Radioastronomia)
The results of two experiments carried out with a large volume balloon-borne omnidirectional plastic scintillator sensitive to high-energy gamma-radiation are reported here. The flights were carried out on 18 November 1990 and 24 February 1992, at places of 11.1 and 11.5 GV geomagnetic cut-off rigidities, respectively. For an omnidirectional detector and for energies greater than several MeV, most of the detected photons are secondary gamma-rays produced through interactions of the charged cosmic rays with the atmosphere. To unfold the observed pulse-height spectrum and obtain the incident gamma-ray spectrum, the detector response is calculated numerically with some simplifying assumptions. By using this response function a differential flux dJ/dE=E-1.2\pm 0.2photons.cm-2.s-1MeV-1, averaged over all zenith angles, is estimated for the atmospheric gamma-ray radiation, at an atmospheric depth of 5 g.cm-2, in the 10-100 MeV energy range. That flux results to be compatible with other observations made with different types of detectors and at different geomagnetic cut-offs.
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