Vacuum Properties of Ti-Mo Getter Material

Accelerator-based boron neutron capture therapy (AB-BNCT) is an emerging modality for cancer treatment. Vacuum deterioration caused by gas injection into the ion source may induce electrical breakdown in the accelerator. Maintaining a high vacuum in the beam transport line is therefore essential for stable accelerator operation. Non-evaporable getter (NEG) pumps feature a compact size, a high pumping speed for hydrogen, and good compatibility with high electric potentials, making them suitable for establishing high- and ultrahigh-vacuum conditions in the beam transport lines of direct-current high-voltage accelerators. The pumping performance of NEG pumps is affected by activation cycles, operating temperature, hydrogen partial pressure, impurity gases, particle irradiation, and high voltage. In this study, the constant-pressure method was employed to investigate the effects of activation cycles, steady-state operating temperature, and hydrogen partial pressure on the specific pumping speed and sorption capacity of a Ti–Mo getter. The adsorption–desorption equilibrium and performance degradation were further analyzed based on Sieverts’ law and microstructural characterization. The results show that the Ti–Mo getter exhibited its highest pumping performance after the second activation cycle. Within the investigated ranges, increasing the operating temperature or hydrogen partial pressure enhanced both the initial specific pumping speed and sorption capacity to varying degrees. Under the hydrogen-loading and pressure conditions employed in this study, the Ti–Mo getter approached a dynamic adsorption–desorption equilibrium at approximately 350℃, whereas hydrogen desorption became dominant at 450℃.