Operational radiation protection challenges for the LHC experiments.

This article focuses on the challenges faced by radiation protection physicists at CERN in assessing residual activation and residual dose rates for the Large Hadron Collider (LHC) experiments during shutdown periods. It presents a novel method based on fluence conversion coefficients, which efficiently converts particle fluences into radiological hazard factors and is implemented with Monte Carlo transport codes such as FLUKA and PHITS. The method's application is demonstrated through the assessment of activation in 600 tons of austenitic stainless steel used in the Compact Muon Solenoid (CMS) High Granularity Calorimeter (HGCal), showing consistency with traditional event-based approaches and advantages in convergence speed and visualization. Additionally, the article discusses the use of FLUKA simulations to estimate residual dose rates around the CMS detector during maintenance configurations, highlighting the flexibility of these tools in optimizing radiation protection measures.