Na 22 activation level measurements of fused silica rods in the LHC target absorber for neutrals compared to simulations

The Target Absorbers for Neutrals (TANs) are located in a high intensity radiation environment inside the tunnel of the Large Hadron Collider (LHC). TANs are positioned about 140 m downstream from the beam interaction points. Seven 40-cm long fused silica rods with different dopant specifications were irradiated in the TAN by the Beam RAte of Neutrals (BRAN) detector group during p+p data taking from 2016 to 2018 at the LHC. The peak dose delivered to the fused silica rods was 18 MGy. We report measurements of the Na22 activation of the fused silica rods carried out at the University of Illinois at Urbana-Champaign and Argonne National Laboratory. At the end of the irradiation campaign, the maximum Na22 activity observed was A=21 kBq/cm3 corresponding to a density, ρ=2.5×1012/cm3, of Na22 nuclei. fluka Monte Carlo simulations have been performed by the CERN fluka team to estimate Na22 activities for the irradiated BRAN rod samples. The simulations reproduce the Na22 activity profile measured along the rods, with a 35% underestimation of the experimental measurement results.