Resonance enhancement of neutrinoless double electron capture

The process of neutrinoless double electron (0νECEC$0\nu \text{ECEC}$) capture is revisited for those cases where the two participating atoms are nearly degenerate in mass. The theoretical framework is the formalism of an oscillation of two atoms with different total lepton number (and parity), one of which can be in an excited state so that mass degeneracy is realized. In such a case and assuming light Majorana neutrinos, the two atoms will be in a mixed configuration with respect to the weak interaction. A resonant enhancement of transitions between such pairs of atoms will occur, which could be detected by the subsequent electromagnetic de-excitation of the excited state of the daughter atom and nucleus. Available data of atomic masses, as well as nuclear and atomic excitations are used to select the most likely candidates for the resonant transitions. Assuming an effective mass for the Majorana neutrino of 1 eV, some half-lives are predicted to be as low as 10²² years in the unitary limit. It is argued that, in order to obtain more accurate predictions for the 0νECEC$0\nu \text{ECEC}$ half-lives, precision mass measurements of the atoms involved are necessary, which can readily be accomplished by today?s high precision Penning traps. Further advancements also require a better understanding of high-lying excited states of the final nuclei (i.e. excitation energy, angular momentum and parity) and the calculation of the nuclear matrix elements.     

Observation of radiative double electron capture for

Radiative double electron capture (RDEC), occurring when two electrons are captured to a projectile ion with the simultaneous emission of a single photon, has been investigated. RDEC can be considered as the time inverse process of double photoionization. Strong evidence for RDEC is found in F⁹⁺ + N₂ collisions and additionally for one-electron F⁸⁺ for which the probability for the process is expected to be considerably smaller. Preliminary values for the cross sections for RDEC have been determined. A significant advantage of the gas target is that multiple-collision effects seen for a solid target are avoided due to the single-collision conditions that prevail for gas targets.     

Search for double electron capture of 106Cd

A search for double electron capture of ¹⁰⁶Cd was performed at the Modane Underground Laboratory (4800 m w.e.) using a low-background and high-sensitivity multidetector spectrometer TGV-2 (Telescope Germanium Vertical). New limits on β ⁺/EC, EC/EC decays of ¹⁰⁶Cd were obtained from preliminary calculations of experimental data accumulated for 4800 h of measurement of 10 g of ¹⁰⁶Cd with enrichment of 75%. They are > 9.1 × 10¹⁸ yr, > 1.9 × 10¹⁹ yr for transitions to the first 2⁺, 511.9 keV excited state of ¹⁰⁶Pd, and > 1.3 × 10¹⁹ yr, > 6.2 × 10¹⁹ yr for transitions to the ground 0⁺ state of ¹⁰⁶Pd. All limits are given at 90% C.L. The text was submitted by the authors in English.     

Internal bremsstrahlung and double internal bremsstrahlung in initial p-state electron capture

Internal bremsstrahlung (IB) and double internal bremsstrahlung (DIB) have been studied for initial p-state electron capture. In the case of IB the relative contributions of discrete and continuum intermediate states have been calculated and, in contrast to IB in initial Is state capture, it has been found that the contributions from the discrete intermediate states are dominant. Calculations for DIB have been extended and some approximations used in earlier calculations are shown to be reasonable. Predictions are made for DIB in the EC decay of SU55 Fe and ¹³¹Cs, nuclei which may be suitable for experimental investigations.     

Neutrinoless double electron capture as a tool to measure the electron neutrino mass

A nucleus (Z, A) may capture two atomic electrons to become (Z ? 2, A). For Majorana neutrinos this may occur with no neutrino emission, the process is a virtual mixing of the parent atom and the daughter atom with two electron holes. The process becomes real as the daughter atom de-excites. In some cases where the daughter nucleus is excited, the neutrinoless decay may be enhanced by its proximity to a virtual resonance. We identify the ${}^{112}\text{Sn}\text{→}{}^{112}\text{Cd}$ transition as a good case. The no-neutrino lifetime for m_ν = 30 eV ranges from 10²² to 10²⁷ years as a function of the insufficiently well determined distance to resonance. The signatures of the two- or no-neutrino modes are very different.     

Nuclear matrix elements for the resonant neutrinoless double electron capture

The rate of the neutrinoless double electron capture ( 0n\ensuremath 0\nu ECEC) decay with a resonance condition depends sensitively on the mass difference between the initial and final nuclei of decay. This is where the JYFLTRAP Penning-trap measurements at the JYFL become invaluable in estimation of the half-lives of these decays. In this work the resonant 0n\ensuremath 0\nu ECEC decay is discussed from the point of view of its theoretical aspects, in particular regarding the resonance condition and the involved nuclear matrix elements (NME). The associated decay amplitudes are derived and the calculations of the NMEs by the microscopic many-body approach of the multiple-commutator model are outlined. The resonant 0n\ensuremath 0\nu ECEC decays of ⁷⁴Ge\ensuremath {\rm ^{74}Ge} and ¹³⁶Ce\ensuremath {\rm ^{136}Ce} are discussed as applications of the theory framework.     

Angular dependence of double electron capture in collisions of C4+ with He

In charge-transfer collisions of C⁴⁺(1s^{2 1}S) with He (1s^{2 1}S), the process of double electron capture into the ground state C²⁺ is well-known to dominate other channels by an order of magnitude for projectile energies below 10 keV. This work presents a calculation of differential cross-sections resolved in the angle and energy gain variables, based on an ab initio treatment of electronic states, and compares with the measurements published in the literature (projectile energy E=270, 400, and 470 eV). We also briefly discuss the semi-empirical two-state models developed by experimentalists for this process.     

An electron paramagnetic resonance study of conformational substate distribution in high spin heme-proteins

The electron paramagnetic resonance spectra of high spin ferric horse myoglobin and human hemoglobin have been analyzed by computer simulation in terms of a distribution of the metal ion crystal field energies Δ₁ and Δ₂. The widths of these distributions have been put into relation 0 to the distribution of the conformational substates which may be sampled by the biomolecules during their physiological activity and become eventually arrested at low temperature. These distributions are found to be dependent upon both the solvent used and the cooling history to which the samples were submitted. The results are discussed in connection with the physical analogies displayed by these biomolecules and the glassy systems in general.     

Image recovery from double amplitudes in fractional Fourier domain

The classical Gerchberg--Saxton algorithm is introduced into the image recovery in fractional Fourier domain after adaptation. When this algorithm is applied directly, its performance is good for smoothed image, but bad for unsmoothed image. Based on the diversity of fractional Fourier transform on its orders, this paper suggests a novel iterative algorithm, which extracts the information of the original image from amplitudes of its fractional Fourier transform at two orders. This new algorithm consists of two independent Gerchberg--Saxton procedures and an averaging operation in each circle. Numerical simulations are carried out to show its validity for both smoothed and unsmoothed images with most pairs of orders in the interval [0, 1].     

Conformational substate distribution in low spin ferric myoglobin as studied by electron paramagnetic resonance

Electron paramagnetic resonance of low spin ferric myoglobin frozen solutions have been analyzed in terms of Gaussian distributions of the tetragonal and rhombic splitting parameters Δ andV. These distributions have been interpreted as arising from the frozen disorder resulting from the presence of a conformational substate distribution of the protein molecules. The parameters characterizing the Δ andV distributions, extracted by computer simulation, are shown to be affected by the solvent composition and by the cooling rate at which the samples are submitted. The results are discussed in relation to the behaviour of the high spin ferric myoglobin samples in the same conditions.     

Double internal bremsstrahlung in electron capture

Double internal bremsstrahlung has been observed in the electron capture decay of ³⁷Ar. The energy distribution of the two photons has been investigated, using a dual parameter pulse-height analysis system, at an angle of θ = 90° between two photon propagation vectors. For sum photon energies in the interval of 210–810 keV and at θ = 90° the ratio of the transition probabilities of double to single bremsstrahlung emissions was found to be (4.8±0.4)×10^?5.     

On neutrinoless double e capture problem

Resonance effects in neutrinoless double e capture are considered. It is shown that observation of these effects in future experiments is a fundamental test of QED. However, preparation of the experiment requires new technologies to be applied in nuclear physics.     

Invariant amplitudes and double dispersion relations for electron-muon scattering

For electron-muon scattering, a set of six invariant amplitudes free from kinematical singularities is determined. A simple proof of this freedom is given. Projection operators for this set are constructed. Double dispersion relations using natural subtraction points are derived for the box diagram.     

Fluorescence induced by double K capture

Features of double fluorescence spectra generated by double K capture in the ⁷⁸Kr atom are considered. The energies and bandwidths of fluorescence are calculated. The latter are approximately four times wider for the first and second quanta, respectively, relative to the vacancy hole in the K shell. The fluorescence yields are calculated as well. They are 0.77 and 0.61 for the first and second quanta, respectively, and 0.47 for both quanta simultaneously.     

Radiative electron capture to the continuum

We have analyzed the process of electron capture to the continuum with photon emission, which is referred to as radiative electron capture (RECC). We have considered different projectiles on He targets, observing the behavior of the differential cross section in the first Born approximation, for asymptotic high velocities. These results have been compared with Dettmann's mechanic electron capture to the continuum (MECC) theory. For He targets we find that the RECC process prevails over MECC when the projectile velocity is greater than 20 au. Furthermore we observed that RECC requires larger velocities to prevail when the target is heavy.     

Thermal electron capture by some chlorobromopropanes

Thermal electron attachment rate constants for CH₂ClCHBrCH₃ and CH₂ClCH₂CH₂Br have been measured using electron swarm method. Corresponding rate constants are equal to 3.5×10^-10 and 2.5×10^-10 cm³ molec^-1 s^-1, respectively. Parallely, negative ion mass spectra of these compounds as well as CH₂FCH₂Br, CH₂ClCH₂Br, CH₂BrCH₂Br and CF₃CHClBr has been measured with negative ion mass spectrometry method. The rate constants have been compared with the negative ion mass spectra.     

Electron capture and loss in electron swarm experiments

The effect of capture and subsequent loss of electrons upon their time distribution in time-of-flight electron swarm experiments has been investigated. It is found that if the mean release time of captured electrons is much smaller than both the drift time and the time width of the electron swarm distribution, the effective diffusion coefficientD′ is given approximately by whereD is the electron diffusion coefficient in the absence of capture,w is the drift velocity, γ is the inverse release time, β is the inverse capture time and ζ=ψ/β+γ It is shown that measurements ofw andD by the steady state Townsend method should be unaffected by temporary capture processes.     

Cascade theory of electron capture in quantum wells

A cascade theory of electron capture in shallow quantum wells, when the capture process is determined by the interaction with acoustic phonons, is constructed. In these conditions, the ejection of electrons falling into a well back to the conduction band is significant. The possibility of electron ejection is taken into account by introducing an sticking probability for electrons located in the well. Such an approach is analogous to the Lax cascade theory of electron capture at small impurity centers. Calculations have been performed for wells 3 and 4 nm in width in the Al_0.05Ga_0.95As/GaAs/Al_0.05Ga_0.95As heterostructure. The developed theory has also made it possible to describe thermal ejection of electrons from shallow quantum wells.