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

Abstract

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 ^{22}Na 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 ^{22}Na activity observed was A=21 kBq/cm^{3} corresponding to a density, ρ=2.5×10^{12}/cm^{3}, of ^{22}Na nuclei. fluka Monte Carlo simulations have been performed by the CERN fluka team to estimate ^{22}Na activities for the irradiated BRAN rod samples. The simulations reproduce the ^{22}Na activity profile measured along the rods, with a 35% underestimation of the experimental measurement results.