Growth Behavior of Tantalum as Hydrogen Diffusion Layer on Copper Substrate Modified by Electrolytic Oxidation for AB-BNCT Target

Tantalum (Ta), with a high hydrogen diffusion coefficient, acts as a hydrogen diffusion layer (H-D layer) in accelerator-based boron neutron capture therapy (AB-BNCT) neutron production targets to prevent hydrogen embrittlement of copper (Cu) substrates. However, when Ta layers reach micron-level thicknesses, stress accumulation during magnetron sputtering may cause cracks or peeling. To solve this issue, this study used electrolytic oxidation (EO) to modify surface microstructure of Cu substrates. A three-factor, three-level orthogonal experiment investigated how EO parameters (current density, treatment time, solution temperature) affect surface morphology and crystal structure of Cu substrates, as well as performance of subsequent Ta deposition. Under optimal conditions (10 min reaction time, 20 mA·cm −2 current density, 50℃ solution temperature), surface microstructure of modified substrates provided more attachment points for sputtered Ta atoms and restricted atomic migration. Compared with unmodified substrates (0-Cu), the 1 μm Ta layer on modified substrates (7-Cu) had significantly reduced stress (from 28.27 GPa to 2.11 GPa), enhanced bonding (no detachment or cracking), and a higher β-Ta proportion. Monte-Carlo simulations (PHITS) confirmed that EO-introduced phosphorus (from phosphoric acid electrolyte) did not reduce neutron yield of targets, which remained stable at 2.4×10 13 n·s −1 with 0-20% P content. SRIM simulations further showed excellent proton stopping power of Ta layers, which effectively prevented proton penetration into Cu. This study provides reliable theoretical support and methods for design and manufacture of neutron production target materials.