Extended utilization of a 68Ge/68Ga reference source as a mock 18F source in the ionization chamber calibration

Possible extended utilization of a 68Ge/68Ga source as a surrogate 18F reference source was studied. Some effects and uncertainties might arise from the difference of constructions between chambers that were used in the source calibration and those practically in use. To extend utilization of the surrogate source, response ratio of real 18F to 68Ge/68Ga sources were determined for three models of chambers. Monte-Carlo simulation using EGS5 code was also carried out to evaluate uncertainties expected. The present result shows that such a surrogate source would adapt to calibration even for chambers have with different construction from the reference chamber used as the determination of 18F equivalent activity of the 68Ge/68Ga surrogate source.