Analysis of Radioisotopic Metal Impurities Generated in (O-18) H₂O during F-18 Production with Cyclotron

D. Alloni, M. Prata, B. Smilgys

In this work we present a characterization of the radionuclidic impurities originated by proton irradiation of enriched water [¹⁸O]H₂O in a medical cyclotron through Monte Carlo simulations and experimental measurements. A set of standard samples of enriched water loaded in the cyclotron target cell have been irradiated at 30 µA proton current for one hour each and, after an appropriate cooling time, measured by HPGe gamma spectrometry. In this way it was possible to study the direct release of radionuclidic impurities from target components as well as the release as a function of target ageing. Previously to experimental measurements, Monte Carlo calculations with the Phits Code have been carried out to estimate the radionuclides generated within the target components (in particular Havar^® foil) with the aim to identify the nuclides expected to be found in the irradiated water due to cell-to-water transmission mechanisms. Comparison between simulations data and experimental measurements by gamma spectrometry revealed that only a very small amount of the radionuclides produced in the target window are released in the enriched water through corrosion/erosion effects, while the release decreases with increasing aging of the target.