Investigation of Induced Radioactivity and Dose Distribution in Proton-Irradiated Nitinol SMA at 8.5, 25.5 and 42.5 MeV using FLUKA Simulation

In this study, the dose distribution and induced radioactivity of a proton-irradiated Nitinol (NiTi) shape memory alloy plate with dimensions of 2 × 1 × 0.3 cm were investigated using the FLUKA Monte Carlo code at three different proton energy values of 8.5, 25.5, and 42.5 MeV under a constant beam intensity of 2.0 × 10¹³ p/s. Simulations carried out through the FLUKA/FLAIR interface were used to evaluate the total specific activity, activation-product inventory, residual ambient dose equivalent H*(10) distributions, and neutron fluence spectra at the end of irradiation and after cooling times of 1 hour, 1 day, and 1 week. The results showed that ⁴⁷V was the dominant radionuclide in all energy scenarios. The total specific activity of the sample after irradiation increased from around 1.00 × 10⁷ Bq/g for 8.5 MeV to about 1.12 × 10⁹ Bq/g for 25.5 MeV and 2.30 × 10⁹ Bq/g for 42.5 MeV, respectively, corresponding to an approximately 230-fold increase across the considered energy range. The co-production of ⁴⁸V and ⁶⁴Cu for the 8.5 MeV case is consistent with the radionuclide inventory reported in brachytherapy-oriented activation studies of Nitinol. Maps for residual dose distribution showed that there was maximum radiation field intensity at the center of the implant, which quickly decayed in the initial phase of cooling; however, it remained at high levels after longer cooling time in the higher energy cases. The neutron fluence spectra likewise showed a systematic increase in the secondary radiation field with increasing proton energy, in agreement with the observed activation inventory. Overall, the results provide a structured picture of the energy-dependent activation and dose behavior of proton-irradiated Nitinol. These findings provide a reliable basis for radiation safety assessment, cooling-time optimization, and the planning of future implant-focused proton dosimetry studies.