Multiconfiguration Relativistic Random-phase Approximation Research Articles

Angular and polarization correlations in double-excitation resonances of Mg

Angular distribution and spin polarization of photoelectrons from 3s valence subshell of neutral magnesium are investigated by using the multiconfiguration relativistic random-phase approximation. Photoionization parameters for all five Rydberg series of double-excitation resonances P1o, P1o, and 3D1o between the Mg+[3s] and Mg+[3p] thresholds are presented to clarify the high-energy portion of the Rydberg series, in which peaks corresponding to double excitations can be identified unambiguously.

Constraining neutrino electromagnetic properties by germanium detectors

The electromagnetic properties of neutrinos, which are either trivial or negligible in the context of the Standard Model, can probe new physics and have significant implications in astrophysics and cosmology. The current best direct limits on the neutrino millicharges and magnetic moments are both derived from data taken with germanium detectors with low thresholds at keV levels. In this paper, we discuss in detail a robust, ab initio method: the multiconfiguration relativistic random phase approximation, that enables us to reliably understand the germanium detector response at the sub-keV level, where atomic many-body physics matters. Using existing data with sub-keV thresholds, limits on reactor antineutrino's millicharge, magnetic moment, and charge radius squared are derived. The projected sensitivities for next generation experiments are also given and discussed.

Constraints on millicharged neutrinos via analysis of data from atomic ionizations with germanium detectors at sub-keV sensitivities

With the advent of detectors with sub-keV sensitivities, atomic ionization has been identified as a promising avenue to probe possible neutrino electromagnetic properties. The interaction cross sections induced by millicharged neutrinos are evaluated with the ab initio multiconfiguration relativistic random-phase approximation. There is significant enhancement at atomic binding energies compared to that when the electrons are taken as free particles. Positive signals would distinctly manifest as peaks at specific energies with known intensity ratios. Selected reactor neutrino data with germanium detectors at an analysis threshold as low as 300 eV are studied. No such signatures are observed, and a combined limit on the neutrino charge fraction of $|{\ensuremath{\delta}}_{\mathrm{Q}}|<1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ at 90% confidence level is derived.

Atomic ionization of germanium by neutrinos from an ab initio approach

An ab initio calculation of atomic ionization of germanium by neutrinos was carried out in the framework of multiconfiguration relativistic random phase approximation and benchmarked by related atomic structure and photoabsorption data. This improves over the conventional approach based on scattering off free electrons whose validity at sub-keV energy transfer is questionable. Limits on neutrino magnetic moments are derived using reactor neutrino data taken with low threshold germanium detectors. Future applications of these atomic techniques will greatly reduce the atomic uncertainties in low-energy neutrino and dark matter detections.

Photoionization Processes of the Single-Ionized Boron

The relativistic calculations of the cross-section σ, the angular-distribution parameter β, and spin-polarization parameters {ξ,η,ζ} of photoelectrons using the multiconfiguration relativistic random-phase approximation theory for the photoionization of the B+ ion are presented. Precise energies and widths of all five Rydberg series of doublyexcited states (2pns)1P1o, (2pns)3P1o, (2pnd)1P1o, (2pnd)3P1o, and (2pnd)3D1o are determined. Our predictions are in very close agreement with experiments and are consistent with other calculations.

Applications of the relativistic equation of motion to photoionization of Mg-like ions

As an approximation to the relativistic equation of motion, the multiconfiguration relativistic random-phase approximation theory is applied to the valence-shell photoionization of the Mg-like ions. Photoionization cross sections between ( 2 p 6 3 s ) 2 S 1 / 2 and ( 2 p 6 3 p ) 2 P 1 / 2 0 ionization thresholds are calculated. The main feature of our results is exhibited by five Rydberg series of doubly excited states arising from fine-structure splittings. A comparative study of Al +, Si 2+, P 3+, S 4+, Cl 5+, and Ar 6+ is presented.

Photoionization of Be, B+, C2+, N3+, O4+, and F5+ in the MCRRPA theory

The multiconfiguration relativistic random-phase approximation theory is applied to the valence-shell photoionization along the Be isoelectronic sequence. Photoionization cross sections between (1s22s)2S1/2 and (1s22p)2P°1/2 ionization thresholds are calculated. There are five Rydberg series of doubly excited states that manifest themselves as autoionization resonances in the photoionization cross section. A comparative study of Be, B+, C2+, N3+, O4+, and F5+ is presented.

Photoionization processes of the beryllium atom

The cross section $\ensuremath{\sigma}$, angular-distribution parameter $\ensuremath{\beta}$, and spin-polarization parameters ${\ensuremath{\xi},\ensuremath{\eta},\ensuremath{\zeta}}$ of photoelectrons for neutral beryllium are calculated in the multiconfiguration relativistic random-phase approximation theory. Precise energies and widths of all five Rydberg series of doubly excited states $(2pns)^{1}P_{1}^{\mathrm{o}}$, $(2pns)^{3}P_{1}^{\mathrm{o}}$, $(2pnd)^{1}P_{1}^{\mathrm{o}}$, $(2pnd)^{3}P_{1}^{\mathrm{o}}$, and $(2pnd)^{3}D_{1}^{\mathrm{o}}$ are given. Experimental studies of the angular distribution and spin polarization of photoelectrons are suggested to obtain information on energies and widths of states, which cannot be obtained from total cross-section measurements.

Spin-Orbit and Core-Shielding Effects on Double-Excitation Resonances of Zn

Autoionization resonances of doubly excited states in the photoionization spectrum of the neutral Zn atom are calculated by using the multiconfiguration relativistic random-phase approximation theory. The cross section, angular distribution, and spin polarization of photoelectrons from the valence subshell 4 $s$ show strong dependence both on the spin-orbit and the core-shielding effects, and good agreements are obtained with available experimental measurements.

Core-polarization effects on near-threshold photoionization of Mg

The multiconfiguration relativistic random-phase approximation theory (MCRRPA) is applied to the photoionization processes of Mg. Double-electron excitations as well as core-electron excitations are included. The core-electron excitations account for the core-valence correlations, specifically the core-polarization effects, and the double-electron excitations account for the intravalence correlations. We obtain a prediction of the ${3s}_{1/2}$ threshold photoionization cross section that is in excellent agreement with experiment. It shows that the core-polarization effects in addition to the double-electron excitations play an important role in the near- threshold photoionization processes of Mg and the MCRRPA provides an accurate account of these effects.

Photoionization of strontium above the 5p3/2 threshold using the multiconfiguration relativistic random-phase approximation

The multiconfiguration relativistic random-phase approximation theory is applied to photoionization of the valence subshells 5s1/2, 4d3/2, 4d5/2, 5P1/2 and 5p3/2 of the Sr atom above the 5p3/2 threshold. Electron correlations associated with double-electron excitations and core polarizations have caused drastic variations in subshell cross sections, branching ratios, angular distributions and spin polarizations of the photoelectrons.

Photoionization of magnesium including double excitations.

The multiconfiguration relativistic random-phase approximation is applied to the photoionization of magnesium. Autoionization resonances between the 3${\mathit{s}}_{1/2}$ and 3${\mathit{p}}_{1/2}$ ionization thresholds are investigated. The main feature of our results is exhibited by three Rydberg series: the broad 3pns $^{1}$${\mathit{P}}_{1}$ series, the narrow 3pnd $^{1}$${\mathit{P}}_{1}$ series, and the 3pns $^{3}$${\mathit{P}}_{1}$ series caused by the fine-structure splittings. Our predictions of the resonance positions are in excellent agreement with experiment, and are consistent with other calculations. For photon energies above the 3${\mathit{p}}_{3/2}$ threshold, cross sections and spin polarizations of photoelectrons from the ionization channels Mg \ensuremath{\rightarrow}${\mathrm{Mg}}^{+}$${(}^{2}$${\mathit{S}}_{1/2}$)+${\mathit{e}}^{\mathrm{\ensuremath{-}}}$, Mg \ensuremath{\rightarrow}${\mathrm{Mg}}^{+}$${(}^{2}$${\mathit{P}}_{1/2}^{\mathit{o}}$)+${\mathit{e}}^{\mathrm{\ensuremath{-}}}$, and Mg \ensuremath{\rightarrow}${\mathrm{Mg}}^{+}$${(}^{2}$${\mathit{P}}_{3/2}^{\mathit{o}}$)+${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ are obtained and compared with other theoretical results.

Relativistic excitation energies and oscillator strengths for transitions in Zn-like ions including core-polarization effects.

Excitation energies and oscillator strengths from the $^{1}$${\mathit{S}}_{0}$ ground state to the first $^{3}$${\mathit{P}}_{1}^{\mathit{o}}$ and $^{1}$${\mathit{P}}_{1}^{\mathit{o}}$ excited states of Zn-like ions are calculated by using the multiconfiguration relativistic random-phase approximation including excitation channels from core electrons. The disagreements among theories and experiments are much reduced but in general remain.

Relativistic excitation energies and oscillator strengths including core-polarization effects for the intercombination and resonance transitions in Mg-like ions

Excitation energies and oscillator strengths from the 1S0 ground state to the first 3P10 and 1P10 excited states of Mg-like ions are calculated using the multiconfiguration relativistic random-phase approximation including excitation channels from core electrons. The discrepancies between the relativistic random-phase approximation calculation and experimental results for the intercombination excitation energies and oscillator strengths are much reduced. The excitation energies and oscillator strengths for the resonance transition from the multiconfiguration relativistic random-phase approximation are in excellent agreement with experiment. A substantial part of the discrepancy in the 3P10-1P10 separations is resolved when core excitation channels are taken into account.

Core-polarization effects in the 3P 1o 1P 1o separations of Cd- and Hg-like ions

The 3P 1 o 1P 1 o separations of Cd- and Hg-like ions from the multiconfiguration relativistic random-phase approximation including core-excitation channels are compared with those from other theories and with experiment. The present ab initio results are generally in better agreement with experiment than those from semiempirical theories.

Core-polarization effects for the intercombination and resonance transitions in Cd-like ions.

Excitation energies and oscillator strengths from the [sup 1][ital S][sub 0] ground state to the first [sup 3][ital P][sub 1][sup [ital o]] and [sup 1][ital P][sub 1][sup [ital o]] excited states of Cd-like ions are calculated by using the multiconfiguration relativistic random-phase approximation including excitation channels from core electrons. The discrepancies among theories and experiments are much reduced but, in general, remain.

Core-polarization effects for the (6s2) 1S0 to (6s6p) 3P10, 1P10 transitions in Hg-like ions

Excitation energies and oscillator strengths from the 1S0 ground state to the first 3P10 and 1P10 excited states of Hg-like ions are calculated by using the multiconfiguration relativistic random-phase approximation including excitation channels from core electrons. The discrepancies between the theoretical and experimental results are much reduced for the oscillator strengths but more enhanced for the excitation energies when these core-polarization effects are taken into account.

Comment on "Relativistic excitation energies and oscillator strengths for the 6s2 1S0-->6s6p 1P1,3P1 transitions in Hg-like ions"

In a recent paper, Chou and Huang [Phys. Rev. A 45, 1403 (1992)] employ the multiconfiguration relativistic random-phase approximation (MCRRPA) in an attempt to remove discrepancies between experimental and theoretical oscillator strengths for the 6${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}6s6p $^{1}$${\mathit{P}}_{1}$, $^{3}$${\mathit{P}}_{1}$ transitions in mercurylike ions. Their MCRRPA results are found to be still in poor agreement with beam-foil measurements, and the authors suggest that a significant part of this disagreement may arise from ``an improper account of the cascade effects in beam-foil lifetime measurements.'' However, Chou and Huang have overlooked several, more recent beam-foil measurements in which ``proper'' account has been taken of cascading by the application of an arbitrarily-normalized-decay-curve technique with which their MCRRPA results are still in poor agreement. We conclude that this disagreement is mainly due to the omission by Chou and Huang from their calculation of core-polarization effects. In fact, calculations in which such effects are included show quite satisfactory agreement with the beam-foil measurements in which an account of cascade effects has been taken.

Relativistic excitation energies and oscillator strengths for the (5s2)1S0-->(5s5p)1P1,3P1 transitions in Cd-like ions.

Excitation energies and oscillator strengths from the $^{1}$${\mathit{S}}_{0}$ ground state to the first $^{3}$${\mathit{P}}_{1}$ and $^{1}$${\mathit{P}}_{1}$ excited states of Cd-like ions are calculated by using the multiconfiguration relativistic random-phase approximation. Results are compared with other theories and with experiment. The discrepancy between the theoretical and experimental results is discussed.

Double-excitation effects on the angular distribution of photoelectrons from strontium.

The interplay between relativistic and electron correlation effects on the angular distribution of photoelectrons from strontium is studied by using the multiconfiguration relativistic random-phase approximation theory. Our results show a much shallower dip in the angular asymmetry parameter for photoelectrons from subshell 5${\mathit{s}}_{1/2}$ when double-electron excitations are included in the calculation. Measurements are called for to verify the effects.