C Michotte

On decay constants and orbital distance to the Sun—part III: beta plus and electron capture decay

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 22Na, 54Mn, 55Fe, 57Co, 65Zn, 82+85Sr, 90Sr, 109Cd, 124Sb, 133Ba, 152Eu, and 207Bi 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 Earths orbital distance to the sun could not be observed within 10−4–10−5 range precision. The most stable activity measurements of β + 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.

On decay constants and orbital distance to the Sun—part II: beta minus decay

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 Earths 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.

On decay constants and orbital distance to the Sun - Part I: Alpha decay

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 Earths orbital distance to the sun could not be observed within 10(-5)-10(-6) range precision.

Update of the BIPM comparison BIPM.RI(II)-K1.F-18 of activity measurements of the radionuclide 18F to include the PTB

Since 2001, six national metrology institutes (NMIs) have submitted six samples of known activity of 18F to the International Reference System (SIR) for activity comparison at the Bureau International des Poids et Mesures (BIPM), the most recent being that of the PTB (Germany). The activities ranged from about 1 MBq to 18 MBq. The key comparison reference value (KCRV) has been recalculated to include the latest value, with the agreement of the CCRI(II). The degrees of equivalence between each equivalent activity measured in the SIR have been recalculated and the results are given in the form of a matrix. A graphical presentation is also given for this key comparison with identifier BIPM.RI(II)-K1.F-18. 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 Section II of the Consultative Committee for Ionizing Radiation (CCRI(II)), according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Evidence against solar influence on nuclear decay constants

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 comparison CCRI(II)-S7 on the analysis of uncertainty budgets for 4πβγ coincidence counting

Detailed uncertainty reporting is imperative for proficiency tests and comparison exercises because uncertainties need to be comparable and trusted by all the participants. Even though participants do their best to follow the Guide to the Expression of Uncertainty in Measurement, ambiguities and divergences about uncertainty evaluation remain. Consequently, to analyze the situation, the CCRI (II) Uncertainties Working Group proposed a comparison exercise (CCRI(II)-S7) about the uncertainty evaluation of a relatively simple primary activity measurement: the standardization of a 60Co source by coincidence counting. To be able to understand how various NMIs calculate coincidence counting uncertainties, our study focused on two of the dominant uncertainty components commonly quoted for 4πβ-γ coincidence counting in the International Reference System (SIR) submissions and Key Comparison exercises: efficiency-extrapolation and weighing. Participants from twelve different laboratories were sent the same set of measurement data from the analysis of a 60Co solution standardized at the National Physical Laboratory (NPL). Our study demonstrated the extent of the different interpretations of the uncertainty components. Some factors causing large discrepancies were isolated and are discussed. Further studies of other techniques using a similar approach would be beneficial for the metrology community. 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).

Towards a new GUM—an update

The contents of the current edition, JCGM 100:2008, of the Guide to the Expression of Uncertainty in Measurement (GUM) and its Supplements are reviewed and remarks made concerning a proposed revision of the GUM. A committee draft of the revision was circulated to member organizations of the Joint Committee for Guides in Metrology (JCGM) and all national metrology institutes in December 2014. The motivation for the proposed changes is given and reactions to the committee draft are summarized. Some of the contents of this paper are solely an expression by the authors and do not constitute an official statement by the JCGM.

Uncertainty evaluation in activity measurements using ionization chambers

Pressurized re-entrant (or 4π) ionization chambers (ICs) connected to current-measuring electronics are used for activity measurements of photon emitting radionuclides and some beta emitters in the fields of metrology and nuclear medicine. As a secondary method, these instruments need to be calibrated with appropriate activity standards from primary or direct standardization. The use of these instruments over 50 years has been well described in numerous publications, such as the Monographie BIPM-4 and the special issue of Metrologia on radionuclide metrology (Ratel 2007 Metrologia 44 S7–16, Schrader1997 Activity Measurements With Ionization Chambers (Monographie BIPM-4) Schrader 2007 Metrologia 44 S53–66, Cox et al 2007 Measurement Modelling of the International Reference System (SIR) for Gamma-Emitting Radionuclides (Monographie BIPM-7)). The present work describes the principles of activity measurements, calibrations, and impurity corrections using pressurized ionization chambers in the first part and the uncertainty analysis illustrated with example uncertainty budgets from routine source-calibration as well as from an international reference system (SIR) measurement in the second part.

Comparisons CCRI(II)-K3.F-18 and APMP.RI(II)-K3.F-18 of activity measurements of the radionuclide 18F and links to the key comparison reference value of the BIPM.RI(II)-K1.F-18 comparison

In 2003, the CCRI(II) decided that an indirect comparison of 18 F measurements piloted by the National Physical Laboratory (NPL), UK in 2001 was sufficiently well constructed that it could be converted into a CCRI(II) comparison, with comparison identifier CCRI(II)-K3.F-18. At the same time, the pilot laboratory made a bilateral comparison with the institute in Chinese Taipei, comparison identifier APMP.RI(II)-K3.F-18. The results of the comparisons have been reported and the key comparison working group (KCWG) of the CCRI(II) has approved the mechanism to link all the results to the key comparison reference value (KCRV) of 18 F. The KCRV has been determined through the International Reference System (SIR) for activity comparison at the Bureau International des Poids et Mesures (BIPM), with comparison identifier BIPM.RI(II)-K1.F-18. These comparisons have enabled a further four results to be added to the matrix of degrees of equivalence for 18 F activity measurements.

CCRI(II) activity comparison of 241Pu: CCRI(II)-K2.Pu-241

In 2010, seven laboratories took part in the CCRI(II) key comparison of activity concentration measurements of 241Pu, CCRI(II)-K2.Pu-241, using seven different methods. The spread of all results except one is 4 × 10−2 in relative terms. The results based on the CIEMAT/NIST efficiency tracing method are shown to be dependent on the beta spectrum shape selected and further work is proposed. The key comparison reference value has been determined as the arithmetic mean of six independent results based on four different methods. The results of the comparison have been analyzed with respect to the key comparison reference value. The degrees of equivalence relative to the key comparison reference value have been approved by the CCRI(II) and are published in the BIPM key comparison database. 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).