The National Metrology Institute of Japan plan to use an inner-through-type ionization chamber (IC) as a working standard to calibrate radon monitors. Novel methods to calibrate the IC were described, and the calibration factor, CF [Bq m -3 A-1], of the IC with its expanded uncertainty (k = 2) was evaluated to be (2.0 ± 0.2) × 1016 Bq m-3 A-1 in the order of 10-13 A in the IC output current. In this study, the CFs, evaluated under sampling conditions between continuous gas flowing and stationary gas filled inside the IC, were in agreement within the uncertainty.
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