Design of beam instrumentation for in-vacuum materials irradiation and testing in a 30 MeV medical cyclotron

摘要

We summarize the studies carried out in Turkish Atomic Energy Authority Proton Accelerator Facility (TAEA PAF) R&D irradiation vault in order to design an in-vacuum fully automated irradiation system capable of adjusting proton beam energy between 2-30 MeV with beam currents down to picoamperes. The low current beam may be used for a wide range of research covering radiation damage testing and non-destructive material analysis such as PIXE, PIGE and RBS. The energy and current of the beam extracted TAEA-PAF cyclotron are not suitable to perform aforementioned applications since the accelerator was primarily designed for radioisotope production. Additional systems such as an energy degrader system, a collimator, an irradiation chamber and a Faraday Cup was designed in order to adjust beam parameters. The effects of different degrader foil materials, thicknesses, configurations and different collimator apertures on the beam energy and current at the target plane were investigated in the design of the energy degrader system. The temperature increase and activation of degrader foils were calculated depending on beam current and irradiation time. The design includes an energy measurement system with a Si(Li) detector. The design of the irradiation chamber includes equipment for beam characterization and sample manipulation and connection ports for detectors, pneumatic cylinders, motors and vacuum components. A Faraday Cup and related low noise electronics were designed, manufactured and tested. Picoampere range beam current was measured successfully with the Faraday Cup and related electronics for design validation.