The international reference system (SIR) is characterized by its high stability and its simplicity. Since it came into existence, about 900 measurements have been made with over 60 radionuclides giving a total of about 650 independent results and interest in the method remains high. The results of the measurements are published in the KCDB and are used to construct the efficiency curve of the ionization chamber (IC) as a function of -ray energy.
To date, the following radionuclides have been measured in the SIR:
Use of a liquid scintillation techniques has allowed the SIR to be extended to include beta-ray emitters.
For the measurement of short-lived radionuclides the BIPM has developed a transportable transfer instrument (TI) that has already been taken to the NIST (USA) for the comparison of Tc-99m activity measurements. Some photographs of the TI are presented
here. The protocol for the BIPM.RI(II)-K4.Tc-99m comparison using the TI is available in the KCDB.
Information for NMIs wishing to participate in the SIR is provided here.
The electronics of the SIR have been updated and verification measurements are in progress.
The high stability of the SIR over more than 30 years