Estimation of carbon-ion-caused radiation levels by calculating the transport of the produced neutrons through shielding layers

G. Fehrenbacher, F. Gutermuth, T. Radon GSI Darmstadt, Germany An important aspect to be considered when designing the GSI future project will be the radiation protection of both the staff and the environment. One of the prerequisites for a permission for the operation of a high-energy accelerator is a careful planning of the necessary radiation shielding equipment. In order to give recommendations for the amount of concrete needed for adequate radiation shielding one has to calculate the transport of the primary produced radiation through the shielding walls. Here we report on using the radiation transport code FLUKA [1] for the evaluation of the shielding design of a medical radiation treatment unit [2]. As an example the irradiation room of the planned heavy-ion cancer therapy facility in Heidelberg is subject to an radiation protection analysis. Neutrons of a wide energy range mainly constitute the radiation impact behind the shielding walls. The production of neutrons by a 400 MeV/u carbon beam in tissue-equivalent material has been measured at the HIMAC in Chiba [3]. Using the computer program FLUKA these primary neutrons are further transported through the shielding geometry by Monte-Carlo techniques. For comparison a conventional line-of-sight model is applied, too. The shielding equipment of the treatment rooms in Heidelberg will consist of two main components, one solid iron block placed directly behind the patient and a thick wall made of concrete surrounding the room. The geometrical arrangement of the design is illustrated in figure 1.