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This work explores the primary activity standardisation of 32Si as part of the SINCHRON project that aims at filling the geochronological dating gap by making a new precise measurement of the half-life of this nuclide. The stability of some of the radioactive test solutions, providing 32Si as hexafluorosilicic acid (H 2 32SiF 6), was monitored over long periods, pointing to the adequate sample composition and vial type to ensure stability. These solutions were standardised using liquid scintillation counting with the triple to double coincidence ratio (TDCR) technique and the CIEMAT-NIST efficiency tracing (CNET) method. Complementary backup measurements, using 4πβ-γ coincidence counting with 60Co as a tracer, were performed with both liquid and plastic scintillation for beta detection. While 60Co coincidence tracing with a liquid scintillator predicted activities in agreement with the TDCR and CNET determinations, using plastic scintillation turned out to be unfeasible as the addition of lanthanum nitrate and ammonia to fix the silicon during the drying process generated large crystals that compromised the linearity of the efficiency function. • Several 32Si solutions were standardised using the TDCR and CNET methods. • Issues with a tritium impurity and long-term stability were dealt with effectively. • β(LS)-γ coincidence tracing with 60Co supports TDCR and CNET determinations. • 60Co tracing with plastic scintillation is unfeasible because of severe self-absorption. • 32Si activity can be determined with about 0.4% relative standard uncertainty. [ABSTRACT FROM AUTHOR]

177Lu decays through low-energy β-- and γ-emissions in addition to conversion and Auger electrons. To support the use of this radiopharmaceutical in Switzerland, a 177Lu solution was standardised using the β-γ coincidence technique, as well as the TDCR method. The solution had no 177mLu impurity. Primary coincidence measurements, with plastic scintillators for beta detection, were carried out using both analogue and digital electronics. TDCR measurements using only defocusing were also made. Monte Carlo calculations were used to compute the detection efficiency. The coincidence measurements with both analogue and digital electronics are compatible within one standard uncertainty, but they are lower than (and discrepant with) the TDCR measurements. An ampoule of this solution was submitted to the BIPM as a contribution to the Système International de Référence. • 177Lu was standardised with the β-γ coincidence and TDCR techniques. • Analogue and digital coincidence measurements are self-consistent and compatible within one standard uncertainty. • β-γ coincidence measurements are 1.8% lower than the TDCR determination. [ABSTRACT FROM AUTHOR]

A triple-to-double coincidence ratio (TDCR) counter was recently constructed at IRA-METAS for liquid scintillation based primary activity standardisations. A description of its optical chamber, efficiency change tools, photomultiplier tubes (PMTs) and electronics is given. This TDCR system was validated by measuring several standard solutions of beta emitters including 45 Ca, 14 C, 63 Ni and 3 H. The activity concentrations, obtained from these measurements and efficiencies computed with a FORTRAN code we developed for symmetric and asymmetric PMTs, agree with the certified values within uncertainties. [ABSTRACT FROM AUTHOR]

Abstract: The work presented here is a new and precise measurement of the half-life of 166mHo by determining the activity concentration, using an ionisation chamber calibrated for this nuclide, and measuring the number of 166mHo atoms using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). Since the isotope 166Er interferes with the mass spectrometric measurement, Er has to be eliminated from the 166mHo radioactive solution. The elimination was achieved using ion-exchange chromatography with the cation exchange resin Dowex AG 50W-X8 and 2-Hydroxybutanoic acid as the mobile phase. After a first transit through the chromatographic column, the purified 166mHo eluate was spiked with natural Er to get a resulting Er isotopic composition close to that of natural Er at better than 99.5%, and then it underwent two further separations to eliminate the Er. The activity concentration of this Er-free radioactive 166mHo solution was measured in our reference ionisation chamber calibrated for this nuclide by means of the 4πβ(PC)-γ and 4πβ(PS)-4πγ coincidence techniques and integral counting with a well-type NaI(Tl) detector and Monte Carlo efficiencies. An aliquot of this standardized solution was sent to the Paul Scherrer Institute (PSI) for mass concentration determination using an isotope dilution MC-ICP-MS approach. The mass concentration of 166mHo in this solution was determined with 0.25% relative standard uncertainty. This value was corroborated by two other independent measurements. The new half-life of 166mHo, 1132.6(39) years (k=1), is compatible with the value determined in 1965, but is 5.6% shorter and about 43 times more precise. [Copyright &y& Elsevier]

Abstract: Primary activity standardisations were performed on solutions of 18F using 4πβ–γ coincidence counting and liquid scintillation counting (LSC) according to the CIEMAT/NIST method. A β +-emission probability of 96.86% was used for both methods. The various standardised 18F solutions were measured in ionisation chambers of the Physikalisch-Technische Bundesanstalt (PTB) and compared by determining radionuclide calibration factors. Already in 2001 an 18F solution had been standardised at the PTB and compared with the results of nine national metrology institutes (NMIs), using the ISOCAL IV secondary radionuclide calibrators of the National Physical Laboratory (NPL) as transfer instruments and a 68Ge check source solution. These results were linked to the International Reference System (SIR) at the Bureau International des Poids et Mesures (BIPM) by aliquots of solutions sent by the Laboratoire National Henri Becquerel (BNM-LNHB) and the NPL. Further on, in 2005, PTB sent an aliquot of an 18F solution to the SIR for ionisation chamber measurements. A value of the equivalent activity was determined and included in the key comparison database (KCDB). The recent PTB value of the equivalent activity of the SIR is in good agreement with the key comparison reference value determined from five NMIs. These results confirm that the standardisation of 18F solutions can be achieved with the accuracy required for use in nuclear medicine and, in particular, for applications in positron emission tomography (PET). [Copyright &y& Elsevier]

Abstract: Theory and experiment of photon–photon coincidence counting with distance variation for activity standardisation of radionuclide solutions are described. The activity of an I-125 solution from an international comparison organised by the BIPM in 2004 was determined. The value obtained agrees with other methods within a limit of 0.2%. The extension of this activity standardisation method to other radionuclides such as Cd-109 with I-125 as a tracer nuclide, In-111, Am-241 and I-124 with a radionuclidic impurity of I-125 is studied. Achieved uncertainties of the activities of Cd-109 and In-111 are of the order of 1.5%. The activity values of sources of Am-241 are determined relative to each other. Am-241 is used for checking the measuring system and as a long-lived reference source. After decay of the order of several I-124 half-lives, sources of I-124 with I-125 are measured to determine the I-125 activity portion. [Copyright &y& Elsevier]

We report here on the primary activity standardisation of a223Ra dichloride solution in equilibrium with its decay daughters. Both the triple-to-double-coincidence-ratio (TDCR) method with an in-house TDCR detector and the CIEMAT-NIST efficiency tracing (CNET) technique with a commercial counter were used. The liquid scintillation efficiencies for both methods are about 6 while the activities they predict with about 0.4% relative standard uncertainty agree within 0.15%. For backup, the solution was also standardised with 4πγ NaI(Tl) integral counting with a well-type NaI(Tl) detector, and efficiencies computed by Monte Carlo simulations using the GEANT code. This simple technique, unused previously for this nuclide, yielded an activity concentration compatible with, but 1% lower than, the one determined by liquid scintillation counting. • 223Ra was standardised with the TDCR and CNET methods. • Activities predicted by these techniques are compatible within 0.15%. • 223Ra was also standardised with gamma integral counting and MC efficiencies. • This technique unused before for 223Ra yields activities compatible with LSC results. [ABSTRACT FROM AUTHOR]

161Tb, which emits low-energy β−- and γ-particles in addition to conversion and Auger electrons, has aroused increased interest for medical imaging and therapy. To support the use of this radionuclide, a161Tb solution was standardised using the β-γ coincidence technique, as well as the TDCR method. The solution had 4.5·10−3% of 160Tb impurities. Primary coincidence measurements, with plastic or liquid scintillators for beta detection, were carried out using both analogue and digital electronics. TDCR measurements using defocusing, grey filtering and quenching for varying the efficiency were also made. Monte Carlo calculations were used to compute the detection efficiency. The coincidence measurements with analogue electronics and the TDCR show a good consistency, and are compatible with the digital coincidence results within uncertainties. An ampoule of this solution was submitted to the BIPM as a contribution to the international reference system. • 161Tb has aroused increased interest recently for medical imaging and therapy. • 161Tb was standardised using the β(PS,LS)-γ(CeBr 3) coincidence techniques. • 161Tb was also standardised with the TDCR method using MC electron spectra. • Coincidence results are consistent with TDCR measurements. • An ampoule of the solution was submitted to the International Reference System. [ABSTRACT FROM AUTHOR]

The activity of a 85Sr solution was determined by means of fully digital 4πβ(LS)-γ anticoincidence counting. The measurements were carried out in a custom-built, combined TDCR / 4πβ(LS)-γ coincidence system, utilising a commercially available CAEN N6751C digitizer. The analysis of the experimental data, collected in list-mode format, was performed off-line by using the SoftKAM computer code developed at PTB. The data were also used to determine the half-life of the 514 keV level of 85Rb which was found to be (1020.2 ± 6.0) ns. • The activity of 85Sr was measured using 4πβ(LS)-γ anticoincidence counting. • The half-life of the 514 keV level of 85Rb was determined. • Measurements were carried out with a digitizer-based DAQ. [ABSTRACT FROM AUTHOR]