Penetration of ionizing radiation from ATLAS cavern into USA15 measured by MPX detectors

The attenuation of the ionizing radiation through a concrete wall between the ATLAS Cavern UX15 and Service Cavern USA15 was measured during LHC collisions in 2012 with two ATLAS-MPX detectors. The detectors were mounted on either side of the wall separating UX15 and USA15. The average cluster counts of photons and charged particles, and thermal neutron fluence per unit integrated luminosity were determined with both detectors. It was found that the cluster counts and thermal neutron fluence were attenuated by two orders of magnitude by the concrete wall. The cluster count on the USA15 side caused by LHC collisions reaches roughly 30% of the level of the natural radiation background at the same position, for a luminosity of 6 x 10(33) cm(-2) s(-1).