Radiation background simulation and verification at the LHC: examples from the ATLAS experiment and its upgrades.

The high collision rates at the new energy regime of the LHC gives rise to unprecedented radiation environments, especially in the inner regions of the experiments. High fidelity codes such as FLUKA and GEANT4 are necessary for simulating the complex radiation environments in detail. The results are used for predicting detector system behaviour and performance over the lifetime of the project. In this paper the Monte Carlo tools used to simulate the radiation backgrounds are discussed and examples of the predictions in the ATLAS inner detector regions are shown. Also presented are the results of verification studies in which the fluence and dose predictions are compared with measurements using recent LHC data. It is shown that the level of agreement has exceeded expectations, with differences typically less than 30%, and always smaller than a factor of two. Finally, the radiation background situation for vertex detectors at the HL-LHC is discussed, as well as a parameterisation of the fluences as a function of centre of mass energy.