Double Electron Capture Research Articles

Hydrogen and helium charge exchange collisions at kiloelectronvolt energies: an electron–nuclear dynamics review

The electron transfer processes that occur during the collision of ions with atomic and molecular systems are of fundamental importance in the understanding of neutralization, fragmentation and bond rearrangement. In this work we present a review of the actual state in charge exchange processes in the few electronvolts up to several kiloelectronvolts within the electron–nuclear dynamics approach. We present the effects of single and double electron capture on stopping power, molecular fragmentation, differential and total cross sections. For the case of α particles, we present the effects of the target mass (target isotopic effect) when colliding with H, D and T atoms, together with the question of control of charge transfer by means of a short, intense laser pulse.

Quadrupolar correlations and deformation effect on two-neutrino εβ+ and εε modes of 156Dy isotope

The two-neutrino positron double-β decay modes of 156Dy isotope are studied in the projected Hartree–Fock–Bogoliubov framework for the 0+ → 0+ transition. Theoretically calculated half-lives of electron–positron conversion and double-electron capture modes are presented. The effect of the quadrupolar deformation on the nuclear transition matrix element M2ν is also investigated.

Radiative Double Electron Capture in Collisions ofO8+Ions with Carbon

Multielectron capture processes observed in low energy collisions of bare ions with target atoms open insight into electron correlations in electromagnetic fields. Radiative double electron capture (RDEC) provides the simplest tool for investigation of such processes. Here, the experimental observation of the RDEC process in collisions of O8+ ions with thin carbon films is presented and the RDEC cross section value obtained is compared with recent theoretical calculations.

Double-β-decayQvalues ofSe74andGe76

The atomic masses of $^{74}\mathrm{Ge}$, $^{74}\mathrm{Se}$, $^{76}\mathrm{Ge}$, and $^{76}\mathrm{Se}$ have been determined from cyclotron frequency ratios of pairs of ions simultaneously trapped in a cryogenic Penning trap. Allowing for cancellation of systematic errors in the mass differences between isobars, we determine the $Q$ value for double-electron capture of $^{74}\mathrm{Se}$ to be 1209.240(7) keV, and the $Q$ value for double-electron emission of $^{76}\mathrm{Ge}$ to be 2039.061(7) keV. The new ${Q}_{2\mathrm{EC}}$ value for $^{74}\mathrm{Se}$ precludes a large resonant enhancement for neutrinoless double-electron capture.

Review of theories on double electron capture in fast ion-atom collisions

This work reviews quantum-mechanical four-body distorted wave theories for double electron capture in collisions between fast heavy multiply charged ions and heliumlike atomic systems. The widely used distorted wave methods of the first- and second-order in the pertinent perturbation series expansions are compared with each other. This tests the presumed importance of double continuum intermediate states of two electrons. Further, the relative performance is evaluated of the second-order theories with and without the eikonalization of the two-electron Coulomb wave functions for double continuum intermediate states. This checks the correctness and usefulness of the eikonalized Coulomb waves when two electrons participate actively to the transition from the initial to the final state of the entire system. We also analyze the significance of the contributions from excited heliumlike states especially in comparison between theory and measurement. The overall goal of the present study is to determine how much of the unprecedented experience gained over several decades in studying high-energy theories of pure three-body charge exchange could be exported directly to four-body double-electron capture without much of additional and essential eleaborations, besides the naturally increased computational demand. In particular, we address the unexpected breakdown of the continuum distorted wave eikonal initial state approximation and the anticipated success of continuum distorted wave theory for double charge exchange in ion-atom collisions at high impact energies.

Double electron capture by protons in collisions with H2

Abstract Double electron capture of protons in collisions with molecular hydrogen in the energy range 1.5–10 keV was studied by measuring the resulting H - velocity distributions. In this paper, a technique that provides experimental evidence about double capture mechanisms is proposed. In addition, cross-sections for this process were measured in the energy range of 1–5 keV.

Double beta decay: A problem of particle, nuclear and atomic physics

A brief review of recent progress in the field of double beta decay is presented. Different aspects from particle, nuclear and atomic physics of both two-neutrino ( 2 ν β β ) and neutrinoless ( 0 ν β β ) modes of the double β decay are discussed. It is argued that the R-parity violating supersymmetry ( ⁄ R p SUSY) contributes to the 0 ν β β -decay predominantly via charged pion-exchange between decaying nucleons. Further, a problem of reliable determination of the 0 ν β β -decay nuclear matrix elements (NMEs) is addressed. It is manifested that the uncertainty associated with the calculation of the 0 ν β β -decay NMEs can be diminished by suitably chosen nuclear probes. A new possibility for the study of lepton number non-conservation is proposed, namely oscillations plus deexcitations of neutral atoms. A phenomenological analysis of this process leads to a resonant enhancement of the neutrinoless double electron capture, that has a Breit–Wigner form.

Nuclear matrix elements for rare decays

Neutrinoless double electron capture ( 0 ν ECEC) is being vigorously investigated because of the possibility of it telling us something about the absolute mass scale of the neutrino. The resonant 0 ν ECEC is particularly interesting due to the potentially huge enhancement of its decay rate by a resonance condition. Recently the mass differences of two atom pairs were measured in order to study the enhancement of the 0 ν ECEC rates of 74Se and 112Sn. The associated nuclear matrix elements were also evaluated. The neutrino mass can also be detected by using beta decays with low Q values. Related to this we have investigated the second-forbidden decay branch of 115In with its ultra-low Q value. Open questions about nuclear and atomic contributions to the associated decay rate emerge.

Cross section invertion between double electron capture and transfer ionisation in low energy collision of highly charged ion(4≤q≤7) with He

Based on the potential parameter Ω, which was defined as energy deposits ratio of incidence ion with target ion after double electron capture, the selection rule between double electron capture and transfer ionization of helium target induced by Aq+ (q=4,5,6,7) ions was studied. It is found that there is a cross point for the cross-section ratio curve of double electron capture and transfer ionization at Ω=10, and for ΩΩ≥10 the transfer ionization is a key reaction channel of double electron transfer.

Search for double beta decay of zinc and tungsten with low background ZnWO4 crystal scintillators

Double beta processes in 64Zn, 70Zn, 180W, and 186W have been searched for with the help of low background ZnWO4 crystal scintillators at the Gran Sasso National Laboratories of the INFN (Italy). The total measurement time exceeds ten thousand hours. New improved half-life (T1/2) limits on double electron capture and electron capture with positron emission in 64Zn have been set. New T1/2 bounds were also set on different modes of 2β processes in 70Zn, 180W, and 186W. Future perspectives are considered.

Double electron capture cross-sections by protons in collisions with He

Double electron capture (DEC) by protons from He was studied in collisions at energies in the keV regime, theoretically and experimentally. Theoretical cross-sections were calculated using the electron nuclear dynamic approach and a binomial distribution method in the energy range 1–100 keV. Experimental cross-sections were measured by means of the grow-rate method in the energy range of 4–10 keV. The cross-sections measured are consistent with those of the previous data at the high energies of the measured interval and show a different trend for the low energy. This behavior is consistent with those of other DEC cross-sections measured by protons from He-like targets. With the two collision models, it is proven that the reference data for this system are consistent only with the assumption of uncorrelated electrons and with independent target-projectile nuclei dynamics.

Differential, partial and total electron capture cross sections in p-Ar collisions

We discuss the results, from two approaches, on electron capture processes in p+Ar collisions: one based on a single-particle approximation, and the other, on a full electron-nuclear dynamics approach. This work presents differential, total and state to state single electron capture and double electron capture in the energy range from 10 eV to 100 keV. When appropriate we compare the results coming from the two methods, which leads us to discuss the effect of the straight line trajectory approximation and the interference effects in cross sections by different projectile trajectories that have the same scattering angle.

Focusing effects by one and two Coulomb centers in the autoionization of He

In this work we consider the autoionization of He following double electron capture in He2+ + H2 collisions at an impact energy of 14 keV/amu. The post-collisional interaction with the two Coulomb centers is treated within the Barrachina-Macek model by employing the Φ2 correlated wave function introduced by Gasaneo et al to represent the continuum of the emitted electron in the field of two Coulomb centers. We compare the angular profiles in the electron spectrum with those obtained following double electron capture for the collision system He2++ He. Clear differences are observed in the spectra obtained for the atomic and molecular targets.

State selective electron capture in slow 15N7++ He, Ne collisions studied using cold-target recoil-ion-momentum spectroscopy

Electron capture from He and Ne targets by 15N7+ has been studied at projectile velocities of 0.27 and 0.5 a.u. Cold-target recoil-ion momentum spectroscopy was used to simultaneously measure the Q-value and scattering angle. Projectile velocity and target dependence comparisons of single and double electron capture by the projectile were carried out. Single capture from both targets populates the same excited states with nearly similar angular distributions and relative populations. The populated channels in double capture from He and Ne, however, are quite different. One-step and two-step capture mechanisms are proposed for most of the populated channels in double capture.

Young-type interferences in double-electron capture

We have measured the dependence on the molecular orientation of the cross section for two-electron transfer from hydrogen molecules to fast (1.2 and 2.0 MeV kinetic energy) He2+ ions. A very strong angular dependence is found, where the maximum and minimum cross sections differ by more than a factor of three. Further the angular dependencies are markedly different for the two different projectile energies. The variations are explained as resulting from the interference of two waves describing projectiles neutralized in the proximity of either of the two target protons. The molecular axis orientation determines the phase difference of these two waves and thereby affects the cross section.

Double charge transfer reaction involving highly charged ions Neq+ (q=1-10) and neutral helium

Double and single electron capture processes of helium atoms by Neq+ (q=1-10) impact have been theoretically investigated using the four-body formalism of quantum mechanical approach.

Correlated radiative double electron capture (RDEC) in collisions of bare oxygen ions with carbon targets

Multielectron capture processes observed in low energy collisions of bare ions give insight into electron-electron correlations in strong fields. The main intention of this experiment is to observe radiative double electron capture (RDEC) in collisions of bare oxygen ions at energies of a few MeV/u with carbon targets. Measured results are to be compared with recent theoretical calculations.

Electron loss and multiple electron capture of Li-like ions colliding with Ne and Ar targets

Absolute cross sections for projectile single electron loss and single and double electron capture of B2+and C3+ ions colliding with Ne and Ar in the energy range from 0.1 to 4.0 MeV were measured. Calculations for the single capture channel were performed using the Bohr-Lindhard model, showing good agreement with the experiment. For the single electron loss, calculations were made using an extended version of the free-collision model for the screening mechanism, added to antiscreening cross sections calculated within the PWBA. The calculations provided very good descriptions of the measured data. Scaling laws were obtained for the single-electron loss by both targets.

Energy dependence of multi-electron transfer reactions between slow multi-charged ions and neutral atoms

Using an ion-spectroscopy method, charge transfer reactions between slow multi-charged Arq+(q=3~5) ions and neutral Ar atoms have been studied in the laboratory collision energies from 3.1 to 4.6keV. The energy gain spectra of single-electron capture processes show no strong energy dependence. On the contrary, those of double-electron capture processes depend on the collision energy.

Double-electron-capture cross sections forLi3+collisions with He at intermediate-to-high velocities

We have measured double-electron capture cross sections for ${\text{Li}}^{3+}$ projectiles and He targets in the 2.0--5.5 MeV energy range (3.4--5.6 a.u. velocity range). Double-electron-capture cross sections for this collision system were measured before, but only at relatively lower energies. There is a good agreement between the three available sets of experimental data for double capture at the lower end of the present data energy interval, i.e., where the ranges from different measurements overlap. The present measurements for other collision channels that include single and double ionization, single capture, and transfer ionization corroborate the reliability of the data normalization adopted in our work. Our experimental data for double capture are compared with the corresponding theories in order to assess the relative performance of the main two strategies, the semiclassical independent particle model, and the full quantum-mechanical four-body theories. We thoroughly discuss possible reasons for the discrepancies among various theoretical predictions from these two frameworks and point out several potential paths for their improvement.