Thermosyphon Targets Designed for the Production of 18F for use in Positron Emission Tomography

Abstract

¹⁸F is a radioisotope commonly used in Positron Emission Tomography. One way to produce ¹⁸F is to bombard ¹⁸O enriched water with protons, generated by a cyclotron. The production reaction is ¹⁸>O(p,n) ¹⁸F. The purpose of this research was to model and build a more efficient target that can withstand higher proton beam currents and energies and produce greater yields of ¹⁸F. A thermosyphon was chosen as the basis for the target design. Thermosyphons transfer heat through evaporation and condensation. The concept is simple; the target water is allowed to boil and the water vapor rises out of the target chamber into a condenser region that is cooled along the outer surface. Condensation occurs along the condenser walls, and the condensate then runs down the length of the cylinder and back into the target chamber.

The thermosyphon target model showed that this form of target design was feasible, withstanding greater proton beam currents and energies and producing more ¹⁸F than conventional targetry. Three separate thermosyphon targets, each increasing in condenser heat transfer surface area and volume, were built and their performance was experimentally validated. The results of both the model and the experimental targets are discussed in detail.