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I.N. Azcarate (IAR, Argentina)
An experiment carried out with a collimated gamma-ray detector is described. The detector system was transported by an stratospheric balloon, that was launched from Parana, Provincia de Entre Rios, Argentina, on 18 November 1992 ( geomagnetic cut-off 11.1 GV). The presence of a peak was observed, as a characteristic feature of the energy-loss spectrum in the detector. That peak corresponds to the 511 keV line produced by positron annihilation in both the atmopsphere and the lead collimator. The contribution to the counting rate ``below" the peak due to the 511 keV photons produced in the lead is computed. The resulting flux for the atmospheric 511 keV line, at an atmospheric depth of 4.5 g.cm-2, is (9 ± 0.07) x 10-2 phot. cm-2.s-1, which is compatible with measurements performed at other geomagnetic latitudes. Upper limits for other atmospheric gamma-ray lines fluxes are obtained.\\
Acknowledgements : This research was partially supported by grant PIP 0430/98 from CONICET, from Argentina. I.N. Azcarate is a member of the Carrera del Investigador Cientifico y Tecnologico from CONICET, Argentina.
The author(s) of this abstract have provided an email address for comments about the abstract: iazcarate@yahoo.com
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.