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MEASUREMENTS WITH A Ge DETECTOR AND MONTE CARLO COMPUTATIONS OF DOSE RATE YIELDS DUE TO COSMIC MUONS

Clouvas, A.; Xanthos, S.; Antonopoulos-Domis, M.; Silva, J.

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Abstract— The present work shows how portable Ge detectors can be useful for measurements of the dose rate due to ionizing cosmic radiation. The methodology proposed converts the cosmic radiation induced background in a Ge crystal (energy range above 3 MeV) to the absorbed dose rate due to muons, which are responsible for 75% of the cosmic radiation dose rate at sea level. The key point is to observe in the high energy range (above 20 MeV) the broad muon peak resulting from the most probable energy loss of muons in the Ge detector. An energy shift of the muon peak was observed, as expected, for increasing dimensions of three Ge crystals (10%, 20%, and 70% efficiency). Taking into account the dimensions of the three detectors the location of the three muon peaks was reproduced by Monte Carlo computations using the GEANT code. The absorbed dose rate due to muons has been measured in 50 indoor and outdoor locations at Thessaloniki, the second largest town of Greece, with a portable Ge detector and converted to the absorbed dose rate due to muons in an ICRU sphere representing the human body by using a factor derived from Monte Carlo computations. The outdoor and indoor mean muon dose rate was 25 nGy h−1 and 17.8 nGy h−1, respectively. The shielding factor for the 40 indoor measurements ranges from 0.5 to 0.9 with a most probable value between 0.7–0.8.

* Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, GR-54006 Thessaloniki; Universite Pierre et Marie Curie (Paris VI), France, U.F.R. Physique BC 210, 4, Place Jussieu, 75252 Paris cedex 05.

Manuscript received 26 October 2001;

revised manuscript received 7 June 2002, accepted 26 August 2002

For correspondence or reprints contact: A. Clouvas, Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, GR-54006 Thessaloniki, Greece, or email at clouvas@eng.autho.gr.

© 2003 by the Health Physics Society