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 col- limator. 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.