ASSESSMENT OF COSMIC-RAY IONIZING COMPONENT AT GROUND-LEVEL BY MEANS OF HPGE SPECTROMETRY

Experimental assessment of the cosmic ray ionising component at ground level has been carried out using a high purity germanium(HPGe) spectr ometry system together with a NaI(TI) scintillation detector. A 14 lit re spherical ionisation chamber was used simultaneously in order to di stinguish between the dose rate from gamma rays below 3 MeV and that f rom the cosmic ray ionising component detected in the higher energy re gion. Various cosmic ray dose rates and corresponding count rates were made available by utilising the shielding effect of a multi-storied b uilding, including measurements at an outdoor flat and a mountain top. As a result Y = 30.25 X(G) + 1.42 and Y = 19.83 X(N) + 1.32 were deri ved, where Y is dose rate due to cosmic ray ionisation in nGy h(-1), a nd X(G) and X(N) are the corresponding count rates in cps measured by the HPGe and NaI(TI) spectrometers, respectively, in the region of 3 t o 100 MeV.