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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 40 K decay, with an update of the recommended values for the branching ratios and the total decay half-life. [ABSTRACT FROM AUTHOR]

To test the relevance of the most common assumptions in the calculation of beta (β) and neutrino (ν) spectra, a database of measured shape factors was created, containing 130 distinct transitions. Some analysis parameters were defined to characterize the quality of the calculated spectra. Results from this systematic comparison between theory and experiment are presented in detail. The λk=1 approximation for forbidden unique transitions is shown to be systematically worse than the correct calculation of the theoretical shape factors, where the energy dependence of the λk parameters is included. Regarding forbidden nonunique transitions, the ξ approximation is found to be valid for only about half of the first forbidden nonunique transitions and incorrect in all other cases. The criterion 2ξ/E0≫1 is proved to be insufficient in itself if 2ξ/E0<100. [ABSTRACT FROM AUTHOR]

Metallic magnetic calorimeters have been used for several years for the determination of the shapes of beta spectra. Experimental spectra of the beta decays of $$^{63}$$ Ni and $$^{241}$$ Pu exhibit, at very low energy, strong deviations from standard theoretical calculations including corrections for screening, radiative, and nuclear size effects. These discrepancies can be attributed to the atomic exchange effect. In particular the spectrum of $$^{63}$$ Ni measured with an electroplated $$^{63}$$ Ni source is in excellent agreement with theory including the exchange effect. This underlines the quality of the experimental spectrum as well as the correctness of the calculation of the exchange effect. [ABSTRACT FROM AUTHOR]

Nuclear decay data measurements were performed in the frame of a EURAMET project. Two specific goals were addressed: (1) High-precision measurements of ^238U alpha-particle emission probabilities and (2) experimental characterization of the shape of beta spectra using cryogenic detectors. In the paper, specific lessons learned from the metrological work are highlighted. This includes effects of source preparation on the quality of alpha and beta spectrometry, the influence of exchange effects on beta spectra and the use of a magnet system to eliminate coincidence effects by conversion electrons in alpha-particle spectra. [ABSTRACT FROM PUBLISHER]

Abstract: The low-lying spectroscopy of 6He was investigated via the 2-neutron transfer reaction with the 8He beam delivered by the SPIRAL facility at . The light charged particles produced by the direct reactions were measured using the MUST2 Si-strip telescope array. Above the known state, two new resonances were observed: at (width ) and at with . Through the analysis of the angular distributions, they correspond to a state and to an state, respectively. These new states, challenging the nuclear theories, could be used as benchmarks for checking the microscopic inputs of the newly improved structure models, and should trigger development of models including the treatments of both core excitation and continuum coupling effects. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The 8He(rf, p) reaction was studied in inverse kinematics at 15.4A MeV using the MUST2 Si-Csl array in order to shed light on the level structure of 9He. The well known l6O(d, p)17O reaction, performed here in reverse kinematics, was used as a test to validate the experimental methods. The 9He missing mass spectrum was deduced from the kinetic energies and emission angles of the recoiling protons. Several structures were observed above the neutron-emission threshold and the angular distributions were used to deduce the multipolarity of the transitions. This work confirms that the ground state of 9He is located very close to the neutron threshold of 8He and supports the occurrence of parity inversion in 9He. [ABSTRACT FROM AUTHOR]

Abstract: The LNE-LNHB is developing metallic magnetic calorimeters, a specific type of cryogenic detectors, for beta spectrometry. The aim is the determination of the shape factors of beta spectra. Our latest detector has been designed to measure the spectrum of 241Pu, a pure beta emitter with an endpoint energy of 20.8keV. In this paper, the detection principle of metallic magnetic calorimeters is explained and a detailed description is given of the realization of the detector enclosing a 241Pu source inside the detector absorber. A spectrum resulting from our first measurement is shown and compared with a theoretical spectrum. [Copyright &y& Elsevier]

Abstract: The spectroscopy of 27Ne has been investigated through the one-neutron transfer reaction 26Ne()27Ne in inverse kinematics at 9.7 MeV/nucleon. The results strongly support the existence of a low-lying negative parity state in 27Ne, which is a signature of a reduced sd–fp shell gap in the neutron-rich region, at variance with stable nuclei. [Copyright &y& Elsevier]

Sterile neutrinos are natural extensions to the standard model of particle physics and provide a possible portal to the dark sector. We report a new search for the existence of sub-MeV sterile neutrinos using the decay-momentum reconstruction technique in the decay of 7Be. The experiment measures the total energy of the 7Li daughter atom from the electron capture decay of 7Be implanted into sensitive superconducting tunnel junction (STJ) quantum sensors. This first experiment presents data from a single STJ operated at a low count rate for a net total of 28 days, and provides exclusion limits on sterile neutrinos in the mass range from 100 to 850 keV that improve upon previous work by up to an order of magnitude. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Background: The understanding and description of forbidden decays provides interesting challenges for nuclear theory. These calculations could help to test underlying nuclear models and interpret experimental data. Purpose: Compare a direct measurement of the 138Laβ-decay Q value with the β-decay spectrum end-point energy measured by Quarati et al. using LaBr3 detectors [Appl. Radiat. Isot. 108, 30 (2016)]. Use new precise measurements of the 138Laβ-decay and electron capture (EC) Q values to improve theoretical calculations of the β-decay spectrum and EC probabilities. Method: High-precision Penning trap mass spectrometry was used to measure cyclotron frequency ratios of 138La, 138Ce, and 138Ba ions from which β-decay and EC Q values for 138La were obtained. Results: The 138Laβ-decay and EC Q values were measured to be Qβ=1052.42(41) keV and QEC=1748.41(34) keV, improving the precision compared to the values obtained in the most recent atomic mass evaluation [Wang et al., Chin. Phys. C 41, 030003 (2017)] by an order of magnitude. These results are used for improved calculations of the 138Laβ-decay shape factor and EC probabilities. New determinations for the 138Ce 2EC Q value and the atomic masses of 138La, 138Ce, and 138Ba are also reported. Conclusion: The 138Laβ-decay Q value measured by Quarati et al. is in excellent agreement with our new result, which is an order of magnitude more precise. Uncertainties in the shape factor calculations for 138Laβ decay using our new Q value are reduced by an order of magnitude. Uncertainties in the EC probability ratios are also reduced and show improved agreement with experimental data. [ABSTRACT FROM AUTHOR]