231Pa is the longest-lived decay product in the 235U decay chain and precise standards of this radionuclide are required to enable accurate, traceable measurements in nuclear dating applications such as geochronometry and nuclear forensics. Three independent techniques were used at NPL to determine the activity per unit mass of a freshly separated 231Pa solution as part of an international CCRI(II) comparison: CCRI(II)-K2.Pa-231.The first method was defined solid angle α counting and is the first result reported in a BIPM comparison with this instrument. The second method was 4πα liquid scintillation (LS) counting combined with the CIEMAT/NIST method using commercially available LS counters. The third technique used was 4π(LS)α-γ coincidence counting on an NPL-built system comprising an LS counter with dual photomultiplier tubes (PMTs) coupled to a 70% relative efficiency HPGe γ-spectrometer. Excellent agreement between the three methods was obtained.

A comparison of the activity concentration measurement of a 3H2O solution was organized by the LNE-LNHB under the auspices of the CCRI(II). The solution was sent to thirteen laboratories and eleven measurement reports were received. The results, as well as relevant information on the measurement techniques, are presented and analysed in this paper. All results are consistent within uncertainties. As the solution was traceable to the solution used in the CCRI(II)-K2.H-3 comparison in 2009, the results of both comparisons are also presented. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

At the time of publication, radiopharmaceuticals labelled with thorium-227 are in clinical trials in Europe for the treatment of various types of cancer. In part I of this two-part series the primary standardisation of an aqueous solution of 227Th was reported. In part II, the activity derived from the recommended absolute γ-ray emission intensities have been compared to that from the primary standardisation techniques. This comparison showed a negative bias of 4% in the determined activity per unit mass with an 11% spread in the activities determined for the eight most intense γ-ray emissions (Iγ > 1%) from the 227Th α decay. Using the standardised 227Th, measurements of the characteristic γ-ray emissions from the 223Ra excited states were made using a calibrated HPGe γ-ray spectrometer. This has enabled the absolute intensities of 70 γ ray emissions from the 227Th α-decay to be experimentally determined. A significant improvement over the precision of the recommended normalisation scaling factor has been made, with a value of 12.470 (35) % determined. Typically, the precision of the intensities has been improved by an order of magnitude or greater than current recommended values. The correlation matrices for pairs of the most intense γ-ray emission intensities are presented.

Thorium-227 is a potential therapeutic radionuclide for applications in targeted alpha-radioimmunotherapy for the treatment of various types of cancer. To provide nuclear medicine departments involved in Phase I clinical trials traceability to the SI unit of radioactivity (Bq), a standardisation of a radiochemically pure Th-227 aqueous solution has been performed at the National Physical Laboratory. This was achieved via two primary liquid scintillation (LS) techniques -4 pi(LS)-gamma digital coincidence counting (DCC) and 4 pi LS counting. These absolute techniques were supported by the indirect determination of the Th-227 activity via the measurement of the ingrowth and decay rate of the decay progeny by both ionisations chambers and high purity germanium (HPGe) gamma-ray spectrometry. The results of the primary techniques were found to be consistent, both with each other (zeta score = 1.1) and to the decay progeny ingrowth measurements. An activity per unit mass of 20.726 (51) kBq g(-1) was determined for the solution. A procedure has been developed that provided an effective separation of the Th-227 from its decay progeny, which was shown by the effective time zero of the Th-227-Ra-223 nuclear chronometer measured by HPGe gamma-ray spectrometry.

A comparison of calculations of the activity of a 3 H2O liquid scintillation source using the same experimental data set collected at the LNE-LNHB with a triple-to-double coincidence ratio (TDCR) counter was completed. A total of 17 laboratories calculated the activity and standard uncertainty of the LS source using the files with experimental data provided by the LNE-LNHB. The results as well as relevant information on the computation techniques are presented and analysed in this paper. All results are compatible, even if there is a significant dispersion between the reported uncertainties. An output of this comparison is the estimation

Two new participations in the BIPM.RI(II)-K1.Lu-177 comparison have been added to the previous results and this has produced a revised value for the key comparison reference value (KCRV), calculated using the power-moderated weighted mean. A link has been made to the CCRI(II)-K2.Lu-177 comparison held in 2009 through the NPL and IRMM who participated in both comparisons. Two NMIs used the K2 comparison to update their degree of equivalence. The degrees of equivalence between each equivalent activity measured in the International Reference System (SIR) and the KCRV have been calculated and the results are given in the form of a table for the remaining two NMIs in the BIPM.RI(II)-K1.Lu-177 comparison and the nine other participants in the CCRI(II)-K2.Lu-177 comparison. A graphical presentation is also given.

Two new participations in the BIPM.RI(II)-K1.Lu-177 comparison have been added to the previous results and this has produced a revised value for the key comparison reference value (KCRV), calculated using the power-moderated weighted mean. A link has been made to the CCRI(II)-K2.Lu-177 comparison held in 2009 through the NPL and IRMM who participated in both comparisons. Two NMIs used the K2 comparison to update their degree of equivalence. The degrees of equivalence between each equivalent activity measured in the International Reference System (SIR) and the KCRV have been calculated and the results are given in the form of a table for the remaining two NMIs in the BIPM.RI(II)K1.Lu-177 comparison and the nine other participants in the CCRI(II)-K2.Lu-177 comparison. A graphical presentation is also given.

An international Key Comparison of (177)Lu has recently been carried out. Twelve laboratories performed assays for radioactivity content on aliquots of a common master solution of (177)Lu, leading to eleven results submitted for entry into the Key Comparison Database of the Mutual Recognition Arrangement. A proposed Comparison Reference Value (CRV) was calculated to be 3.288(4)MBq/g using all eleven results. Degrees of equivalence and their uncertainties were calculated for each laboratory based on the CRV. Most of the values reported by the participating laboratories were within 0.6% of the CRV.

The National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) for seaweed was developed through an interlaboratory comparison with 24 participants from 16 countries. After evaluating different techniques to calculate certified values for the radionuclides, the median method was found to be the most representative technique. The certified values were provided for 13radionuclides and information values were given for 15 more radionuclides. Results for the natural decay series showed disequilibrium in both the uranium and thorium series.

The results of the eleventh NPL Environmental Radioactivity Comparison Exercise are reported. In general the level of performance for the nuclides in the a/s mixture has improved but there has been a slight reduction in the level of performance for the nuclides in the s/ mixture. The reported data does suggest that some analysts are still not making cascade summing corrections. The lack of data returned for some s- emitting nuclides has made it difficult to assess performance levels.