Radiation studies with FLUKA for the ATLAS detector

Abstract

This work presents a comprehensive investigation of radiation shielding and radiation damage in the ATLAS detector at the Large Hadron Collider (LHC). The research covers several aspects, including the implementation of a spatial binning technique in FLUKA for effective studies of radiation background, the exploration of different configurations of neutron moderators alongside other shielding concepts, and the reevaluation of weighting factors for negative pions based on a new approach.The implemented spatial binning technique in FLUKA enables the integration of simulation results into interactive web pages, allowing for effective representation of material composition, relevant fluences, and time-dependent spectra of absorbed energy dose within the detector.To optimise the shielding of sensitive detector components, a simple model for effective moderator studies complements detailed investigations of radiation transport within the complex ATLAS geometry. The neutron production in the electromagnetic calorimeteris studied to establish a benchmark for the moderator’s efficiency. Simulations with varying boron content are conducted to evaluate the impact on thermal neutron fluence. Potential interactions between different regions of the detector are examined through an analysis of neutron transport. The effects of reducing hydrogen density of moderators in the Inner Detector on neutron fluence and the impact of hydrogen loss due to boron doping are analysed.A significant part of the research focuses on re-evaluating the weighting factors of radiation damage from negative pions. The study utilises a formalism found in the literature to reassess these factors, leading to a better understanding of the damage mechanisms. The new weighting factors take into account the contribution of particles that are completely stopped within the material, an aspect previously neglected. Based on this, a long-standing mystery regarding the discrepancy between data from radiation sensors and simulation results in the ATLAS detector is now better understood.