High sensitive standard measurement to determine strength of an I-125 brachytherapy source

We are encouraged to contribute to strengthen quality assurance which keeps brachytherapy safe and available. For the purpose, we aspire to determine the source strength and establish national metrological standard in Japan. It is necessary to assemble a high sensitive free air chamber for measurement of ionization current derived from the source which is very weak especially in Japan. Total uncertainty for the source strength is promising to meet required value from users of measurement instruments.