radionuclide metrology-SIR

SIR - International Reference System

The International Reference System (SIR ) for gamma-ray emitting radionuclides offers a simple approach for NMIs and DIs to demonstrate equivalence of primary standards. A sample of the primary standard in solution poured in BIPM glass ampoules is sent to the BIPM, where the standard is compared to primary standards from other NMIs/DIs using a high-stability ionization chamber. The results are reported on the Key Comparison Database and can be part of the evidence needed by the independent assessors approving claims for Calibration and Measurement Capabilities.

There are a large number of gamma-ray emitting radionuclides, so it has been agreed by the CCRI that successful participation in the service for one radionuclide can be accepted as demonstrating the capability to standardize other radionuclides using the same technique. The details of this agreement are set out in the Measurement Methods Matrix.

Gamma-ray emitters with short half lives cannot always be measured in the SIR as samples decay in transit. For these radionuclides, an on-site comparison service is available (SIRTI). Some radionuclides do not emit gamma rays or not enough to be measured by the SIR. ESIR based on liquid scintillation counting can measure these specific radionuclides (ESIR).


Radionuclides covered More than 60 radionuclides from 18F to 243Am
BIPM comparator High precision ionization chamber
Quantity compared Activity / Bq
Level Radionuclide dependent (see procedure SIR-T-20 below)
Uncertainty of comparator Depends on the radionuclide and its activity: 0.05 % – 0.5 % (k = 2)
Comparison service identifier BIPM.RI(II)-K1
Underpins equivalence for... Radionuclides set out in the MMM
Validity Results remain valid for 15 years
Key comparison reference value Power-moderated weighted mean of results

Documents SIR

Reference documents

The international reference system for activity measurements of γ-ray emitting nuclides

Rytz A., 1983. The international reference system for activity measurements of γ-ray emitting nuclides. Appl. Rad. Isot., 34, pp 1047-1056

Guidance document

How to participate - SIR

How to participate


SIR/SIRTI reporting form - radioactive solution


Administration procedure/Shipping instructions for comparisons


Procedure to submit a sample for measurement on the SIR

Ionizing Radiation - contact Radionuclides



BIPM Ionizing Radiation Department - Radionuclide Metrology

radionuclide metrology - KCDB