Lead shielding efficiency from the gamma background measurements in the salt cavern of the Polkowice–Sieroszowice copper mine

The studies of lead shielding efficiency from the gamma background measurements were performed in the salt cavern of the copper mine - a site considered for an underground laboratory. Within the energy range of 50–2700 keV, the measured gamma-ray count rates normalized to the mass of the high-purity detectors germanium crystal are 5.93 and 6.32 s(−1)kg(−1) for the used low-background and portable spectrometers, respectively. The gamma-ray flux of 0.124 (2) cm(−2)s(−1) connected with the natural radioisotopes was observed by the portable HPGe, including 0.026 (1) cm(−2)s(−1) contribution of radon decay products, whereas the photon flux at the spectrum continuum was 0.18 (5) cm(−2)s(−1).