Based on previous study, the calculation of electron capture decays has been improved by considering a more accurate atomic model with precise atomic energies, and different radiative corrections ...have been tested. The computer code has been revised in order to greatly speed-up the calculation and has then been coupled with the BetaShape code. The influence of the nuclear component has also been explored using a simple nuclear model. All the calculations are compared with precise measurements available in the literature.
•An improved theoretical model for electron captures is presented.•Influence of precise atomic energies is explored.•Influence of radiative correction is explored.•Influence of the nuclear component is explored.•Calculations are compared with available precise measurements.
Electron capture properties are crucial to establish the decay schemes of numerous radionuclides. The present modelling aims at improving the theoretical estimates of these decays, which are needed ...when no measurement is available. Allowed and forbidden unique transitions are calculated on the basis of precise relativistic wave functions of the atomic electrons, determined in previous work. In this context, correcting for atomic effects is of high importance. The two common approaches from Bahcall and Vatai to correct for the overlap and exchange effects have been extended to every subshell in a unified formulation, with the electron occupation precisely taken into account. The shake-up and shake-off effects, which create secondary vacancies, and the influence of the hole due to the capture process, have been considered. Uncertainties are also estimated. Relative capture probabilities and their ratios, including capture-to-positron ratios, have been found to be in good agreement with a selection of precise measurements. This modelling was then applied to the third forbidden unique transition of 40K decay, with an update of the recommended values for the branching ratios and the total decay half-life.
•An improved modelling for the calculation of electron capture is detailed.•Overlap and exchange effects are corrected using Bahcall's and Vatai's approaches.•Shake-up, shake-off and inner hole effects are approximately corrected.•This modelling was compared with measurements and two other codes.•The decay scheme of 40K was updated using this modelling.
From a review of the available literature, a database of experimental shape factors from measured beta spectra was created in previous work. Classical assumptions applied in beta spectra calculations ...which avoid the determination of the electron and nuclear wave functions were tested by comparison with each measured spectrum present in the database. From this systematic comparison, it was demonstrated that the typical assumption λk=1 is inappropriate for all forbidden unique transitions. Moreover, the equally common ξ-approximation was also proved to be incorrect for about half of the listed first forbidden non-unique transitions and for all second non-unique ones. In present work, this study has been performed once again using an improved analytical screening correction. General results from previous study still remain the same. Except for allowed transitions, the mean energies in current nuclear databases are expected to be erroneous. Some selected beta spectra are also given to illustrate these results.
•Analyzed database of experimental shape factors from measured beta spectra.•Classical and improved beta spectra calculations have been implemented.•Theoretical and measured beta spectra were systematically compared.•The assumption λk=1 is inappropriate for all forbidden unique decays.•The ξ-approximation is incorrect for half of first forbidden non-unique decays.
We investigate the possible origins of the reactor antineutrino anomalies in norm and shape within the framework of a summation model where β^{-} transitions are simulated by a phenomenological model ...of Gamow-Teller decay strength. The general trends of divergence from the Huber-Mueller model on the antineutrino side can be reproduced in both norm and shape. From the exact electron-antineutrino correspondence of the summation model, we predict similar distortions in the electron spectra, suggesting that biases on the reference spectra of fission electrons could be the cause of the anomalies.
Atomic and nuclear data represent an important input for the accuracy of primary activity measurements based on liquid scintillation. In particular, the reliability of β-spectrum computation has been ...investigated for several years through experimental and theoretical studies providing solid evidence for the need to consider the atomic effects. In the present study, the activity standardization of two β-emitting radionuclides (60Co, 106Ru/106Rh) was carried out by means of the 4πβ−γ coincidence and Triple-to-Double Coincidence Ratio (TDCR) methods. The comparison between the activity concentrations given by both primary techniques presents new evidence that a better agreement is obtained when the exchange and screening effects are included in the β-spectra implemented in the model of light emission for TDCR measurements. A new development of a stochastic model based on Geant4 simulations for TDCR calculations is also presented.
•Primary activity measurements of 60Co and 106Ru/106Rh are presented.•Activity assessment with the TDCR method depends on β-spectra computation.•For both radionuclides, the TDCR and 4πβ−γ coincidence results are compared.•Good agreement is obtained when the atomic effects are considered in the β-spectra calculation.
The accurate measurement of beta spectra is highly important in numerous fields such as nuclear energy, nuclear medicine, ionizing radiation metrology and fundamental physics. We have developed a ...beta spectrometer close to 4π configuration based on silicon detectors. The influence of self-absorption has been studied by means of Monte Carlo simulations and the source preparation technique has been optimized consequently. The measured spectra from 133Ba and 36Cl decays have been compared with PENELOPE simulations.
•A beta spectrometer based on Si detectors.•Monte Carlo simulations with PENELOPE.•Influence of radioactive sources.•Preliminary beta spectrum of 36Cl decay.
This article describes the Nuclide++ module developed at LNE-LNHB to simulate the decay schemes related to single or multiple radionuclides, by randomly selecting decay pathways. Written in C++, with ...respect of the Geant4 coding style, this module can be used transparently in Geant4-based simulation applications as an alternative to the existing Radioactive Decay Module (RDM). Nuclide++ takes advantage of the DDEP recommended data, accurate β-emitting spectra calculation and detailed description of the atomic rearrangement. This module can be useful in many applications, especially those involving radioactive sources. The reliability of the module was verified through comparisons with a while chosen radionuclides.
•A C++ module to generate decay schemes of radionuclides with DDEP recommended data is presented.•The module permits to efficiently simulate radioactive sources with single or multiple radionuclides.•Efficiently process complete decay chains, including metastable levels and time dependence of detectors.•The reliability is demonstrated through comparisons with chosen radionuclides.•The module can be used transparently in Geant4-based simulation applications, alternatively to existing Geant4-RDM.
Metallic magnetic calorimeters are a specific type of cryogenic detectors that have been shown to enable precise measurement of the shape of low energy beta spectra. The aim of their use at LNHB is ...the determination of the shape factors of beta spectra. The beta source is enclosed in the detector absorber, allowing for very high detection efficiency. It has turned out that the type of source is of crucial importance for the correctness of the measured spectrum. Spectra of 63Ni measured with several sources prepared by drying a NiCl2 solution differ from one another and from theory, whereas spectra measured with electroplated sources are reproducible and agree with theory. With these latter measurements we could confirm the atomic exchange effect down to very low energy (200eV).
•The beta spectrum of 63Ni was measured with metallic magnetic calorimeters.•Dried sources are not adequate, electroplated sources yield accurate spectra.•The atomic exchange effect was confirmed down to very low energy (200eV).
We report a high-statistics measurement of the L / K orbital electron capture ratio in 7 Be embedded in cryogenic Ta. The thin Ta film formed part of a high-resolution superconducting tunnel junction ...radiation detector that was used to identify the signals from different decay channels. The measured L / K capture ratio of 0.070(7) is significantly larger than the only previous measurement of this quantity and the theoretical predictions that include in-medium effects. This value is a uniquely sensitive probe of the 1s and 2s orbital overlaps with the nucleus and is of relevance to nuclear and atomic physics, as well as Li production in novae and other astrophysical scenarios. This is the first experiment that uses superconducting tunnel junctions for nuclear-recoil detection, opening a new experimental avenue for low-energy precision measurements with rare isotopes.
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