Radiation Shielding Considerations for Cyclotron Operation (Part 1 of 2)

The cyclotron is a type of charged particle accelerator which produces a continuous stream of high energy protons. Targets comprised of stable elemental isotopes are bombarded by these protons to generate medical radioisotopes used for molecular imaging. When the proton beam interacts with the target material, a nuclear reaction occurs, and there is an emission of secondary particles and gamma rays which must have adequate radiation shielding for personnel protection. Neutrons are an emission product that are particularly hazardous as they are highly mutagenic. Considerations in cyclotron vault design and the necessary thickness and composition of shielding material and strategies to reduce the neutron flux during irradiation will be presented. Self shielded cyclotrons which do not require vault are also possible with the advantage of a much smaller space requirement for the cyclotron. Some of the draw-backs and issues with the self-shielded option will also be presented.