Gamma background measurements in the Laboratoire Souterrain de Modane

In situ gamma-ray measurements were taken at six locations in the Modane Underground Laboratory. Count rates for gamma radiation within the energy range of 7–2734 keV varied from 15 to 108 cs-1. The arithmetic mean was 79 cs-1 for measurements taken without a collimator. The metamorphic rocks surrounding the Lab are characterized by low activity concentrations of uranium and thorium equal to 12 and 10 Bq kg-1, respectively