Portability of the calibration of SIR of BIPM to other ionization chambers for radioactivity measurements

Portability of the calibration of the ionisation chambers of the International Reference System, SIR, of the BIPM to other ionisation chambers used for activity measurements and without having direct access to SIR is described. A linear relationship between calibration figures of different ionisation chambers at IRMM, NPL and NAC and 1/Ae of SIR was established. In favourable cases uncertainties of the slope of less than 1% were obtained.