Ion production efficiency of singly charged ion source for heavy-ion cancer therapy with radioactive ions

Ion production efficiency of an electron impact singly charged ion source (SCIS) has been investigated. The SCIS has been developed to be employed for an ISOL (Isotope Separation On-Line) system, which provides ¹¹C ions to treatment rooms for heavy-ion cancer therapy simultaneously with real-time verification of an irradiation field using PET (Positron Emission Tomography). To provide sufficient ¹¹C ions to the treatment rooms, the SCIS has to realize ionization efficiency of 1% for production of singly charged ¹¹C ions. In previous work, the SCIS was designed based on particle in cell simulation. With the fabricated SCIS, we measured the ion production efficiency for CO₂⁺ ion production from CO₂ molecules and that for C⁺ ion production from CH₄ ions. We found that the SCIS achieved the efficiency of ε_C⁺=5x10^-3 (0.5%) for the C⁺ production, and ε_CO2⁺=5.5x10^-2 (5.5%) for CO₂⁺ production. (author)