Evaluation of neutron spectra in the SK cyclotron room under different operation parameters

This work evaluated the neutron spectra induced by a medical used cyclotron. The neutrons were induced during the 18F-radioisotope productions due to the 9.6 MeV proton beam hit 18O-water target and induced (p, n) reactions in this SK Cyclotron. To evaluate the induced neutron doses in the cyclotron room, dual-TLD chips and gold foils with bare and 113Cd covered were used separately to measure thermal neutron doses and fluence rates at positions outside the self-shielding of cyclotron, in the cases of using different targets. Besides, a 6LiI (Eu) detector with Bonner spheres were used and were placed at the specific locations in the cyclotron room to estimate the neutron spectra of using different operation parameters. In the results, the thermal neutron doses at the locations outside the self-shielding of cyclotron in the case of using target 1 were less than that using target 2. However, thermal neutron doses inside the self-shielding in the case of using target 1 were higher than that using target 2. The evaluated neutron spectra inside and outside the self-shielding confirmed the dose results. The impact of the volume of 18O-water target was discussed in this study. In conclusion, the large target volume (target 1) caused the higher production yield of 18F-radioisotope and induced lower dose and softer spectra of neutrons than the small target, under the same operation parameters which were adopted for validation in this study.