Characterisation of the natural gamma-ray background in the underground Callio Lab facility.

Herein, we measured the natural gamma-ray background in a new underground laboratory facility within Pyhäsalmi Mine in Finland at a depth of 1430 m (~4100 m.w.e). The radionuclide compositions of the rocks in the walls along with the shotcrete on the walls were investigated. The specific activities of the natural radionuclides in these materials were calculated. The measured spectra of the natural gamma-ray background and calculated minimal detected activities of several natural and artificial radionuclides are presented.