Calibration and background measurements with a tissue equivalent proportional counter.

A tissue-equivalent-proportional counter (TEPC) instrument has been used as the reference instrument for cosmic radiation measurement at flight altitudes by several institutes. For purposes of characterisation the response of the instrument has been investigated under different standard radiation conditions, in terms of radiation particle, energy and angle of incidence. Photon sources and photon beams of energies up to 6.6 MeV and neutron beams up to 200 MeV were used. To have a better understanding of the shielding influence of the instrument assembly, the angle dependence of response was analysed for several radiation conditions. Specific measurement conditions were simulated with the Monte Carlo transport code, FLUKA. The measured instrument response was compared with simulation results. It was demonstrated, that simulations were very helpful to understand the instrument's response. The TEPC instrument used by the Austrian Research Centre Seibersdorf (ARCS) research simulates the energy deposition in a unit density tissue volume of 2 microm diameter, of similar size to a cell nucleus. Pure propane at low pressure is used as measurement gas. To characterise the instrument at low dose rates background measurements were done 800 m below ground and at the ultra low level laboratory in Gran Sasso, 1380 m below ground. These results were compared with measurements on the Earth's surface at different altitudes on mountains up to 3480 m above sea level. The significant increase of the expected dose rate is well reproduced by the experiments at mountain altitudes. As a result of this study a full characterisation and a thorough understanding of the performance and reliability of the detector was achieved.