Analysis of residual gas from ECR ion source

A technical realization for a positron emitter 11C-beam (R.I.) as an accelerating-beam has been studied at NIRS-HIMAC in order to apply for a heavy-ion therapy. In this study, the calculation result shows the order of 109 ppp of 11C2+ ions will be extracted from the ion source during 18 minutes at 3.3-second intervals with 1-msec beam pulse under one-Ci of 11C-production, where the ionization efficiency of the 11C2+ ion is assumed to be 1%. So that the first object in this study is to measure an ionization efficiency of 11C-gas in an ECR ion source. In order to investigate the efficiency CH4-gas of 0.07 atm·cc/min was used, and equipped a suitable Q-mass gas analyzing system to measure residual gas components evacuated from the ECR. Result show that almost 1% of the ionization efficiency was observed for 2+ and 4+ of 12C-ions, in the measurement of the charge spectrum. On the other hand, unexpected phenomenon was also observed on the ionization process in the ECR. In this paper details of the phenomenon are analyzed. (author)