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The half-lives of 44Sc and 44mSc were measured by following their decay rate using several measurement systems: two ionization chambers and three γ-spectrometry detectors with digital and/or analogue electronics. For 44Sc, the result was the combination of seven half-life values giving a result of 4.042(7) h, which agrees with the last reported value of 4.042(3) h and confirms the near to 2% deviation from the recommended half-life of 3.97(4) h. Scandium-44 is present as an impurity in the production of 44Sc by cyclotron proton irradiation. Its half-life was determined by measurements performed a few days after End of Bomardment (EoB), so that the 44Sc decayed down to a negligible level. Seven measurements were combined to obtain an average of 58.7(3) h, which is in agreement with the recommended value of 58.6(1) h.

Internal Bremsstrahlung (IB) is a continuous electromagnetic radiation accompanying beta decay; however, this process is not considered in radiation protection studies, particularly when estimating exposure from beta-decaying radionuclides. The aims of the present work are: i) to show that neglecting the IB process in Monte Carlo (MC) simulation leads to an underestimation of the energy deposited in a ionization chamber, in the case of a high-energy pure beta emitter such as Yttrium-90 (90Y), and ii) to determine the most reliable choice of source term for 90Y IB to be used in MC simulations. For this radionuclide, commonly employed in nuclear medicine and radiochemistry applications, experimental data acquired with a well ionization chamber have been compared with Monte Carlo (MC) calculations carried out in the GAMOS framework. Simulations that do not include the effect of the IB process, are found to give results underestimating the experimental values by 12–14%. Consequently, two models for the IB energy spectra, previously described by Italiano et al. [1] , have been implemented using MC simulation and a good agreement has been achieved with one of them. We therefore conclude that inclusion of IB process in Monte Carlo simulation packages is advisable for a more accurate and complete treatment of electromagnetic interactions.

The half-lives of

$^{175}$Yb is a radionuclide that can be generated by neutron capture on $^{174}$Yb and whose decay properties make it useful for developing therapeutic radiopharmaceuticals. As it happens with many of the emerging radionuclides for medical uses in recent years, its nuclear data were determined decades ago and are not thoroughly documented nor accurate enough for metrological purposes. The last documented reference for the $^{175}$Yb half-life value is 4.185(1) days and dates back to 1989, so a redetermination of the value was considered appropriate before standardization at the Institute of Radiation Physics (IRA, Lausanne, Switzerland) primary measurements laboratory. Three independent measurement methods were used to this purpose: reference ionization chamber (CIR, $chambre$ $d'ionization$ $de$ $référence$), CeBr$_{3}$ γ-ray detector with digital electronics and a second CeBr$_{3}$ detector with analog electronics and single-channel analyzer (SCA) counting. The value obtained for the $^{175}$Yb half-life is 4.1615(30) days which shows a 0.56% relative deviation to the last nuclear reference value (ENSDF 2004) and is supported with a detailed calculation of the associated uncertainty.

Internal Bremsstrahlung (IB) is a continuous electromagnetic radiation accompanying beta decay; however, this process is not considered in radiation protection studies, particularly when estimating exposure from beta-decaying radionuclides. The aims of the present work are: i) to show that neglecting the IB process in Monte Carlo (MC) simulation leads to an underestimation of the energy deposited in a ionization chamber, in the case of a high-energy pure beta emitter such as Yttrium-90 (

We report here on the primary activity standardisation of a

In this study, the gamma and X-ray emission intensities of

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).

IRA recently launched a project to digitize all the data acquisition systems it uses for primary radionuclide standardizations. It is well-known that the digital approach presents numerous advantages over the traditional analog electronics such as information losslessness, scalability, online and/or offline data processing, and it is also a solution to the growing difficulties to repair or renew ageing modules. As a first step in this wider program, our institute set-up a 4πβ-4πγ digital coincidence counting system, with FPGA (Field Programmable Gate Array)-based commercial boards from National Instruments (NI), to perform data acquisition and offline data analysis. Choosing all components and software from the same supplier provides a full compact and consistent electronic system. To demonstrate and validate the capacity of this system to standardize the activity of radioisotopes, we compare its predictions for the activity concentration of 133Ba, 166mHo and 18F solutions with the results from a coincidence counting system with analog electronics, as well as with the results from other primary methods and a secondary measurement performed with an IG11 ionization chamber (CIR, chambre d'ionization de reference) with an equivalent activity traceable to the Systeme International de Reference.

The gamma and X-ray emission intensities of 169Er were determined using radionuclidically pure 169Er. The activity of the 169Er source was standardized by the triple-to-double-coincidence ratio technique. Three independent measurements were performed to measure the emission intensities using calibrated high-purity germanium spectrometers. The efficiencies were computed with the Monte Carlo method and validated using several experimental measurements. Final results present a large uncertainty reduction compared to previous evaluations. The emission intensities per decay of 169Er are reported as 1.401(40).10−5 for the 109.8 keV line and 1.513(19).10−6 for the 118.2 keV line. The values obtained for the X-ray lines show large discrepancies with the reference values.

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.

This work looks into the tracks of electrons in nanoemulsive scintillating media using the Monte Carlo Geant4-DNA code which simulates event-by-event interactions of electrons in liquid water down to the eV, without resorting to the condensed history method. It demonstrates that the average number of micelles in which electrons deposit energy is quite large, increasing with their emission energy, decreasing with micelle size, and rising with micelle concentration. The probability of an electron ending its track in a micelle is found to be rather large and micelle size-dependent below 1 keV, and approximating the aqueous fraction at higher energies. Analyses of the Monte Carlo estimated energy depositions in the aqueous phase and in the scintillant tell of a micelle quenching effect, with the micelle size shaping the quenching at low energy and the micelle concentration governing it at higher energies. The micelle effect on the 3 H and 63 Ni beta spectra is discussed for a range of micelle sizes and concentrations. This paper also computes the ionisation quenching function using Birk's law whilst considering the full energy losses in the micelles bisecting the electron pathway, and not just that incurred in the primary micelle enclosing the decaying nuclide. The ionisation quenching function is then used to calculate the detection efficiencies for 3 H, 63 Ni, 54 Mn and 55 Fe. The effect of the micelle size is found to be small for beta emitters but significant for the electron capture nuclides. TDCR measurements of 63 Ni samples covering 8 aqueous fractions are analysed with and without explicit treatment of the micelle effect. Activities in the two representations agree within 0.02%. The ratios of the corresponding figures of merit are found to coincide with the scintillant fractions.

The half-life of 137Cs was measured with an ionization chamber by following the decay of 5 sources over a 30 years period between 1983 and 2013. The ratio between the ionization chamber current for the cesium sources and 226Ra source was used for the half-life calculation. The value found for the 137Cs half-life is 10,955.2±10.7 days, where the uncertainty evaluation combines type A and B for one standard deviation.

The stability of 3H and 63Ni samples, made with Ultima Gold and Ultima Gold AB using eight aqueous fractions ranging between 0.1% and 10%, was monitored over a period of 32 weeks. Counting rate losses were measured in all cases, but were found to be particularly severe for samples with low aqueous fractions. Hydrodynamic diameter measurements of the reverse micelles of 3H and 63Ni in Ultima Gold and Ultima Gold AB samples were performed with dynamic light scattering. For Ultima Gold, the micelle diameters were measured to be about 2nm and slightly dependent of the aqueous fraction, while for Ultima Gold AB they were found to vary strongly with the aqueous fraction and range between 1 and 4nm. The hypothesis that the counting rate instabilities derive from changes in the sizes of micelles was tested by measuring them four times over the monitoring period. The measurement results do not support this claim.

International audience; The hypothesis that seasonal changes in proximity to the Sun cause variation of decay constants at permille level has been tested for radionuclides disintegrating through electron capture and beta plus decay. Activity measurements of Na-22, Mn-54, Fe-55, Co-57, Zn-65, Sr82+85, Sr-90, Cd-109, Sb-124, Ba-133, Eu-152, and Bi-207 sources were repeated over periods from 200 d up to more than four decades at 14 laboratories across the globe. Residuals from the exponential nuclear decay curves were inspected for annual oscillations. Systematic deviations from a purely exponential decay curve differ from one data set to another and appear attributable to instabilities in the instrumentation and measurement conditions. Oscillations in phase with Earth's orbital distance to the sun could not be observed within 10(-4)-10(-5) range precision. The most stable activity measurements of beta(+) and EC decaying sources set an upper limit of 0.006% or less to the amplitude of annual oscillations in the decay rate. There are no apparent indications for systematic oscillations at a level of weeks or months.

The radiolanthanide

Signal processing is a core part of any electronic chain for radioactivity measurement systems and can influence measurement results drastically. A thorough study of the different alternatives for this treatment is especially worthwhile when developing a new digital system. This article describes an evaluation performed to optimize the digital pulse processing stage of the β-γ coincidence counting system at the Institute of Radiation Physics (IRA) designated laboratory for the activity unit. This study is a part of IRA's digitalization project to modernize the aging analog electronic hardware of its primary measurement systems. The β-γ coincidence counting system consists of a plastic scintillation detector in the beta channel and a well-type NaI detector in the gamma channel. Six pulse shaping digital filters along with amplitude calculation algorithms were implemented to obtain beta and gamma pulse amplitude values. In addition, four timing digital filters and time pick-off methods were set up to calculate arrival times (timestamps) for the pulses generated by both detectors. Filter parameters and algorithm settings were adjusted to obtain the best performance. Combination of filters into traditional two channel (fast for timing and slow for shaping) or one channel configuration using dCFD (digital constant fraction discrimination) and LE (leading edge) time pick-off methods were also tested and compared to study the whole digital pulse processing system, using both real measurement signals (241Am, 137Cs, 60Co and 166mHo) and simulated reference pulses. The results of these tests were quantified by evaluating the following metrics: processing speed, signal-to-noise ratio (SNR) at different energies, gamma energy resolution, time measurement accuracy, time resolution and detection efficiency. The results of this evaluation provide a rational ground to assess the system and help decide which digital pulse processing (DPP) method should be the most appropriate.

A comparison of calculations of the activity of a 3H2O 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. 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 of the dispersion of TDCR measurement results when measurement conditions are well defined. KEY WORDS FOR SEARCH Radionuclide metrology, supplementary comparison, tritium, liquid scintillation 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).

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.

The radiolanthanide 161Tb is being studied as an alternative to 177Lu for targeted radionuclide tumor therapy. Both β--particle emitters show similar chemical behavior and decay characteristics, but 161Tb delivers additional conversion and Auger electron emissions that may enhance the therapeutic efficacy. In this study, the half-life of 161Tb was determined by a combination of three independent measurement systems: reference ionization chamber (CIR, chambre d'ionization de reference), portable ionization chamber (TCIR) and a CeBr3 γ-emission detector with digital electronics. The half-life determined for 161Tb is 6.953(2) days, showing a significant improvement in the uncertainty, which is one order of magnitude lower, with a deviation of 0.91% from the last nuclear data reference value. The previous large uncertainty of the half-life had a direct impact on activity measurements. Now it is no more an obstacle to a primary standardization.

This report summarises the results for the new BIPM.RI(II)-K1.Ge-68 comparison. Six metrology institutes have participated, enabling the first value of the key comparison reference value(KCRV) to be determined. The KCRV was calculated using the power-moderated weighted mean and the results. A link has been made to the CCRI(II)-K2.Ge-68 comparison held in 2015 through the NIST, NIM,IRA-METAS and the LNE-LNHB who participated in both comparisons. One NMI 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 five NMIs in the BIPM.RI(II)-K1.Ge-68 comparison and the 12 other participants in the CCRI(II)-K2.Ge-68 comparison. A graphical presentation is also given. 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).

Liquid scintillation counting (LSC) is one of the most widely used methods for determining the activity of 241Pu. One of the main challenges of this counting method is the efficiency calibration of the system for the low beta energies of 241Pu (E max = 20.8 keV). In this paper we compare the two most frequently used methods, the CIEMAT/NIST efficiency tracing (CNET) method and the experimental quench correction curve method. Both methods proved to be reliable, and agree within their uncertainties, for the expected quenching conditions of the sources.

International audience; A comparison of calculations of the activity of a $^3$H$_2$O 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 of the dispersion of TDCR measurement results when measurement conditions are well defined.

A portable instrument was developed at the Institute of Radiation Physics (IRA) for on-site radionuclides measurements. It will enable the measurement of short-lived radionuclides in nuclear medicine departments or isotope production centres. The system involves an ionization chamber read directly by an electrometer and it was optimized to ensure a good reproducibility through the selection of an appropriate vial, filling volume and source position in the well chamber, as well as monitoring the external background and performing a detailed uncertainty estimation. The calibration factors were determined using solutions whose activity concentration is traceable to the international reference system using the IRA reference chamber. Currently the transfer ionization chamber is calibrated for F-18, C-11, O-15, N-13, I-131 and Tc-99m. The final instrument is able to measure isotope activities with a relative standard uncertainty not larger than 1%.

International audience; Claims that proximity to the Sun causes variation of decay constants at permille level have been investigated for alpha decaying nuclides. Repeated decay rate measurements of Po-209, Ra-226, Th-228, U-230, and Am-241 sources were performed over periods of 200 d up to two decades at various nuclear metrology institutes around the globe. Residuals from the exponential decay curves were inspected for annual oscillations. Systematic deviations from a purely exponential decay curve differ in amplitude and phase from one data set to another and appear attributable to instabilities in the instrumentation and measurement conditions. The most stable activity measurements of alpha decaying sources set an upper limit between 0.0006% and 0.006% to the amplitude of annual oscillations in the decay rate. There are no apparent indications for systematic oscillations at a level of weeks or months. Oscillations in phase with Earth's orbital distance to the sun could not be observed within 10(-5)-10(-6) range precision.

International audience; Claims that proximity to the Sun causes variations of decay constants at the permille level have been investigated for beta-minus decaying nuclides. Repeated activity measurements of H-3, C-14, Co-60, Kr-85, Sr-90, Sb-124, Cs-134, Cs-137, and Eu-154 sources were performed over periods of 259 d up to 5 decades at various nuclear metrology institutes. Residuals from the exponential decay curves were inspected for annual oscillations. Systematic deviations from a purely exponential decay curve differ in amplitude and phase from one data set to another and appear attributable to instabilities in the instrumentation and measurement conditions. Oscillations in phase with Earth's orbital distance to the Sun could not be observed within 10(-4)-10(-5) range precision. The most stable activity measurements of beta-decaying sources set an upper limit of 0.003%-0.007% to the amplitude of annual oscillations in the decay rate. There are no apparent indications for systematic oscillations at a level of weeks or months.

The stability of

The half-life of

International audience; The hypothesis that proximity to the Sun causes variation of decay constants at permille level has been tested and disproved. Repeated activity measurements of mono-radionuclide sources were performed over periods from 200 days up to four decades at 14 laboratories across the globe. Residuals from the exponential nuclear decay curves were inspected for annual oscillations. Systematic deviations from a purely exponential decay curve differ from one data set to another and are attributable to instabilities in the instrumentation and measurement conditions. The most stable activity measurements of alpha, beta-minus, electron capture, and beta-plus decaying sources set an upper limit of 0.0006% to 0.008% to the amplitude of annual oscillations in the decay rate. Oscillations in phase with Earth's orbital distance to the Sun could not be observed within a 10−6 to 10−5 range of precision. There are also no apparent modulations over periods of weeks or months. Consequently, there is no indication of a natural impediment against sub-permille accuracy in half-life determinations, renormalisation of activity to a distant reference date, application of nuclear dating for archaeology, geo- and cosmochronology, nor in establishing the SI unit becquerel and seeking international equivalence of activity standards.

International audience; 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 Ca-45, C-14, Ni-63 and H-3. 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.