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The development of the high intensity compact neutron source is mainly conducted by using accelerators for medical purposes. Recently, a lot of compact neutron sources have been developed, and most of them are for boron neutron capture therapy (BNCT). Compared with the common accelerators used for industries, accelerators for BNCT have to accelerate a 100 times larger current of charged particles because of the low conversion efficiency of neutron moderators. To attain a reliable target for the BNCT neutron source, two obstacles have to be overcome; radiation damage (blistering) and heat issue. We introduce diffusion bonding method aiming to make defect free Be neutron target and 1 MPa latent heat water-cooling system. We also install beam expansion optics using quadrupole and octupole magnets to reduce the charge density. Our facility has been operating for more than three years from the commissioning period and we report the recent situation as following. 1) Diffusion bonding method was applied to the solid neutron target of Be with latent heat cooling system. 2) Amount of integrated coulomb value of protons implanted to the Be target is nearly 3000 C now 3) Amount of neutron dose rate was measured. 4) A laser reflection microscope (LRM) method has been developed to observe the neutron target condition (especially radiation damage) through viewport with a few meters working distance. 5) Direct observation of the surface of the Be target was done during the period of improving nearly target vacuum and residual radiation conditions. From these evidences, we conclude our neutron target already produces neutrons capable to treat nearly 500 patients of malignant melanoma.

Diffusion bonded Be neutron target using 8MeV proton beam