Ion-production efficiency of a singly charged ion source developed toward a 11C irradiation facility for cancer therapy

The ion-production efficiency of a newly developed singly charged ion source (SCIS) has been investigated to discuss the possibility of it being used in an isotope separation on-line system that provides 11C ions for heavy-ion cancer therapy with simultaneous verification of the irradiation field using positron emission tomography. The SCIS uses a low-energy hollow electron beam to produce singly charged carbon ions efficiently. To deliver sufficient 11C ions to the treatment room from a limited amount of 11C molecules, which are produced from a boron compound target and proton-beam irradiation via the 11B(p,n)11C reaction, the SCIS must have high ion-production efficiency. To realize this high efficiency, the SCIS was designed using a three-dimensional particle-in-cell code in previous work. With the fabricated SCIS, we performed experiments to measure the efficiency of producing CO2+ ions from nonradioactive 12CO2 molecules and C+ ions from nonradioactive 12CH4 molecules. We found that the SCIS achieved efficiencies of εC+=4×10−3 (0.4%) for C+ production and εCO2+=0.107 (10.7%) for CO2+ production.