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).