Dose gradient assessment at the new CERN CHARM irradiation facility

CERN CHARM facility provides a unique complex radiation environment characterized by particle energy spectra representative of high-energy accelerators, ground and atmospheric conditions and space applications. CHARM is conceived to be an irradiation facility for the qualification of large electronic systems and components in a mixed field radiation environment generated from the interaction of a 24 GeV/c proton beam with a copper or aluminium target. A movable shielding made of layers of concrete and iron allows changing the hardness and the particle population (neutron, proton, kaon, pion, muon, electron, positron, and photon) in predefined test locations. To ensure a full representativeness and reproducibility of the tests, an accurate dosimetry of the complex mixed irradiation field is mandatory. The significant size of the available test area, the multiple facility configurations as well as the strong radiation gradient present in some of the test locations make the radiation monitoring a challenge. This work provides a first characterization of the absorbed dose gradient in two specific test locations: T0, a high dose rate test location close the target revolver; R11, a standard test location for irradiation tests on electronics equipment and devices. Experimental measurements conducted with RPL dosimeters and pMOS RadFET sensors were coupled with FLUKA Monte Carlo simulation. The concluding comparison shows an overall good agreement, considering the strong dose gradient and the limitation of the dosimeters in the mixed field environment.