Effect of magnetron sputtering power on structure and properties of Ta films on Cu substrate of neutron production target for accelerator-based boron neutron capture therapy (AB-BNCT)

Tantalum, with a high hydrogen diffusion coefficient, can be used as an interlayer for neutron production target in Accelerator-based Boron Neutron Capture Therapy (AB-BNCT) to prevent hydrogen embrittlement of Cu substrate. Magnetron sputtering technique was employed to deposit Ta films on the Cu Substrate, with sputtering power being a key parameter. This study investigated the effect of sputtering power on the properties of Ta films deposited on Cu substrate through several methods and Monte Carlo simulations (PHITS and SRIM). A turning point was observed at 250 W, beyond and below which increasing sputtering power led to the increase of Ta film thickness, potentially due to changes in the crystalline structure during deposition. The Ta film exhibited superior surface performance at sputtering powers of 300 W and 350 W. The chemical state of Ta was not affected by sputtering power. Thermal conductivity was observed to decrease after Ta deposition. The thickness of Ta film in this study had a negligible effect on neutron energy spectra and angular distribution. Moreover, a Ta film thickness of 20 μm prevented proton deposition and hydrogen embrittlement in the Cu substrate. These findings have important implications for designing and fabricating neutron production target in AB-BNCT.