Gamma-ray measurements of the activated target components in a cyclotron used for positron emission tomography

摘要

The proton irradiation in a PET cyclotron produces radioactive by-products with high levels of activity in the target components, which are strongly dependent on the specific parameters used in the cyclotron facility. Because the target assembly parts must be replaced periodically, external exposure to operators must be assessed. In this work, high-resolution gamma-ray spectrometry was used to determine the activity levels for the specific radionuclides induced in the target components of a medical 9.6 MeV MINItrace cyclotron. The focus was on three target components, which are periodically replaced: Havar foil, Titanium foil and the Helicoflex seal located on the path of the proton beam just in front of the silver vessel containing the enriched water. Eight radionuclides were identified in the Havar foil: Mn-54, Co-56, Co-57, Co-58, Co-60, Tc-95, Cd-109 and Re-183. In the titanium foil, the nuclides Sc-46, V-48, Cr-51, Co-56, Co-57, and Se-75 were identified, while only Cr-51, Co-58, and Co-60 were detected in the Helicoflex seal. The total effective dose rates to which staff are exposed at the moment of replacing the target were calculated. The waste management for these target components was also considered, using the half-lives of the detected radionuclides in order to determine the time necessary for the activity levels in the target components to be below the exemption levels recommended by the IAEA.