[Accurate measurement of doses in the sample chamber of a 137Cs gamma-ray irradiation apparatus].

Dose rates in the sample chamber of a 137Cs gamma-ray irradiation apparatus (Nordion International Inc., Gammacell 40 Exactor) were accurately measured using an ionization chamber dosimeter. The dose rates obtained were 5.2-7.2% higher at the upper and lower planes than at the middle plane in the sample chamber. In the process of starting and stopping the irradiation, the additional dose during the movement of the source (end effects) was evaluated to be 0.85-1.21% (average 1.05 +/- 0.05%) of that estimated from the steady dose rate for 1 min. When the irradiation period was less than 1 min, it was necessary to make a correction for the end effects in order to keep the error in irradiation dose below 1%.