Towards the first collection of 44Sc at CERN MEDICIS

CERN MEDICIS (Medical Isotopes Collected form ISOLDE) is a new facility at CERN, with the aim to extract and collect a large range of radioactive isotopes for research and development in medical applications. The ISOLDE (Isotope Separation On-Line Device) facility receives 1.4 GeV protons from the Proton Synchrotron Booster (PSB) where they impinge a target. However, about 85% of them transverse the target without interacting. By placing the MEDICIS target behind the ISOLDE target, a second life is given to these protons. The nuclear interactions inside the target result in a large variety of isotopes. After the irradiation stage, the target is transported to the MEDICIS facility where the off-line extraction is carried out and the radioactive isotope of interest is collected. The facility includes an experimental hall where employees will be working, even during a batch collection. Since we will be dealing with high activities in the target and the collection point it is of vital importance to evaluate the facility in terms of radiation protection. Exposure to high amounts of radiation can be detrimental for the human body. Therefore, dose limits are set by Swiss legislation and by CERN itself. The facility will need to comply to this limit. The aim of this thesis is to create realistic simulations of the dose distribution in the experimental hall during the collection of Sc-44. FLUKA, a multi-particle Monte Carlo transport code, is used for this purpose. Sc-44 will namely be one of the first isotopes to be collected and was previously determined to be the limiting factor in terms of radiation protection. Doing so, it is possible to determine weak spots in the facility and if any precautions need to be taken. Starting from an initial model of the MEDICIS facility, the model was refined and errors in the geometry were taken out. First, the activated target was included in the geometry. This proved the need of additional shielding in front of a weak spot in the wall separating the target area from the experimental hall. Simulating the expected 1 GBq Sc-44 collection showed that the dose rate in the proximity of the collection point exceeds the specified limit. Additional shielding is in this case not a possibility due to limitations in the budget. The proposed solutions are, therefore, demarcation of the area or imposing a limit on the collected 44Sc activity. This limit was determined to be a 0.1 GBq Sc-44 collection. Finally it was shown that the accumulation of isotopes on parts of the separator assembly is of no concern, as the resulting contribution to the dose is very low.