Atomic Bound State Research Articles

Multiphoton radiative recombination of electron assisted by a laser field

In the presence of an intensive laser field the radiative recombination of the continuum electron into an atomic bound state generally is accompanied by absorption or emission of several laser quanta. The spectrum of emitted photons represents an equidistant pattern with the spacing equal to the laser frequency. The distribution of intensities in this spectrum is studied employing the Keldysh-type approximation, i.e. neglecting interaction of the impact electron with the atomic core in the initial continuum state. Within the adiabatic approximation the scale of emitted photon frequencies is subdivided into classically allowed and classically forbidden domains. The highest intensities correspond to emission frequencies close to the edges of classically allowed domain. The total cross section of electron recombination summed over all emitted photon channels exhibits negligible dependence on the laser field intensity.

Production of anti-hydrogen at CERN

Antihydrogen atoms H0 ≢ pe+, the simplest atomic bound state of antimatter, have been observed using a method which assumes that the production of H0 is predominantly mediated by the e+e−-pair creation via the two—photon mechanism in the antiproton—nucleus interaction. Neutral H0 atoms are identified by a unique sequence of characteristics. In the present investigation we concentrate on the production of this antimatter object only, since so far it had not been observed. The observed yield of the signature for eleven produced antihydrogen atoms, including two possible background events, agrees with theoretical predictions.

Observation of antihydrogen production in flight at CERN

The observation of the production of antihydrogen atoms H0 = pe+, the simplest atomic bound state of antimatter, is presented. A method has been used by the PS210 collaboration at LEAR which assumes that the production of H0 is predominantly mediated by the e+e--pair creation via the two-photon mechanism in the antiproton-nucleus interaction. Neutral H0 atoms are indentified by a unique sequence of characteristics. In principle H0 is well suited for investigations of fundamental CPT violation studies under different forces, however, in our investigations we concentrate on the production of this antimatter object, since so far it had not been observed. The production of eleven antihydrogen atoms is reported including possibly 2 ± 1 background signals, the observed yield agrees with theoretical predictions.

Modified atomic transition rates by plasma ion fields

Atomic transition rates used in plasma modeling are themselves affected by the plasma environment. The effect of plasma ions is conveniently represented by a time-dependent electric field and the resulting changes in the various rates by this field are presented as plasma enhancement factors, in compact and user friendly forms. They apply to radiative deexcitation, collisional excitation and deexcitation, radiative recombination, collisional ionization, three-body recombination and Auger ionization. The enhancement factors are scaled in terms of three parameters; principal quantum number(s) n of atomic bound state(s), plasma density N ̃ = N Z 3 and (ionic) temperature T ̃ p = T p (μ pZ 2) , where Z is the charge of the ionic core. Although the enhancement factors that involve high Rydberg states are as large as 10 3 in the range of interest of N ̃ and T ̃ p , their effects on the plasma kinetics may be small since the atomic rates strongly decrease with n and the role of high Rydberg states is suppressed by plasma field ionization and by Debye shielding.

Production of antihydrogen

Results are presented for a measurement for the production of the antihydrogen atom H 0 ≡ p e + , the simplest atomic bound state of antimatter. A method has been used by the PS210 collaboration at LEAR which assumes that the production of H 0 is predominantly mediated by the e +e −-pair creation via the two-photon mechanism in the antiproton-nucleus interaction. Neutral H 0 atoms are identified by a unique sequence of characteristics. In principle H 0 is well suited for investigations of fundamental CPT violation studies under different forces, however, in our investigations we concentrate on the production of this antimatter object, since so far it has never been observed before. The production of 11 antihydrogen atoms is reported including possibly 2±1 background signals, the observed yield agrees with theoretical predictions.

Elastic scattering of low and intermediate-energy electrons by Kr and Xe atoms

The many-body correlation forces, which act between the impinging electron and the bound electrons of the two heaviest rare gas atoms, are treated here using a newly developed correlation-polarisation potential that originates from the calculation of correlation energies in electronic bound-states of atoms and molecules. The new formulation of such forces, already tested by us for the lighter atomic targets, is particularly effective for the present systems and can be implemented very easily even for heavy atomic targets. The calculations reported in this paper show clearly that very good accord is obtained with more sophisticated theoretical treatments and with several experimental data on integral cross sections, momentum transfer cross sections and angular distributions.

Two-particle states in dense hydrogen plasmas with external electric fields

Atomic bound state energies are drastically changed by many-particle effects such as dynamical self-energy, dynamical screening and Pauli blocking (phase space occupation). The continuum edge is changed, too, so that the effective ionization energy may tend to zero with increasing density and bound states do not exist (Mott effect). Another possibility to influence the energy spectrum is the application of external electrical fields (Strak effect). Both the many-particle effects and the external field lead to a level broadening, i.e., to finite lifetimes of the two-particle states. In this paper, an effective Schrödinger equation is solved which takes into account both influences on the two-particle spectrum and wave functions. Real and imaginary parts of the spectrum are determined using the complex scaling method. The interrelation between external fields and many-particle effects in investigated. The work is of interest for kinetic properties of plasmas with ionization and recombination processes, where there is a competition of the influences mentioned.

The Effect of Continuum-continuum Transitions on Laser-induced Continuum Structures

Abstract Laser induced continuum structures (LICS) can be produced by a strong laser embedding an excited atomic bound state into a flat atomic continuum, leading to a tunable resonance of adjustable width that can be probed by a second laser. If this second laser is of similar intensity to the embedding laser then the distinction between the two becomes artificial and saturation effects become important. In this paper the effect on LICS of transitions caused by both lasers between the original atomic continuum and a second atomic continuum are studied in the Markoff approximation by means of Laplace transform methods and allowing for the ionization of each atomic state by both laser fields. Formal results correct to all orders are also given in terms of a T-matrix approach. Numerical calculations are presented showing the effects on the LICS resonant structures of continuum-continuum coupling processes. Significant changes to the Fano profiles (second laser weak) and to coherence holes (second laser strong) occur. Analytical results are also given.

Studies of weak interaction effects by laser spectroscopy of short-lived atoms

Laser-induced nuclear orientation has been used to make sub-Doppler-resolution measurements of a nuclear isomer85mRb that has a lifetime of only a microsecond. The technique succeeds because the sampled atoms remove themselves before equilibrating. This paper describes two cases in which pre-equilibrium removal of atoms can prevent thermal equilibrium from obscuring information about the weak interaction that is present in the velocity profile of atoms as they recoil following beta decay. It should be possible to measure electron-antineutrino angular correlations in the beta decay of85Kr, and to look for beta decay of tritium into an atomic bound state of3He-a fundamental effect predicted by weak interaction theory but never observed.

Protonium annihilation into two mesons

The annihilation of a protonium atomic bound state into two mesons is analyzed in terms of threshold values of the helicity amplitudes for the annihilation process. One of the mesons is assumed to have spin 0 and the other either spin 0 or 1, all parity combinations being considered. Simple expressions for partial widths are derived and used, together with the total annihilation widths obtained from a parametrized potential to give branching ratios. We also derive expressions for the angular distribution of one meson with respect to the direction of the X-ray emitted in the transition which populated the level. The available experimental branching ratios are used to extract values for various helicity amplitudes. Where possible they are then compared to quark model predictions and to values obtained by extrapolation from higher energies. Reasonable agreement is found except for a quark model prediction for annihilation to π + π − from the 3P 0 level, which gives a much larger rate than the experimental value. This possibility of detailed comparison demonstrates the power of the analysis. Complete experiments are suggested for the determination of all necessary helicity amplitudes describing annihilation from a given atomic bound state.

Atom-Nucleus Hybrid State of 9 Be

A new concept of “atom-nucleus hybrid state” is proposed to explain the second 9ΣBe peak observed in the (K-, π-) reaction at CERN. The explanation is based on coupling among the isotriplet states of 8Be*(16.63 MeV) with corresponding isotriplet of Σ particles. The Coulomb interaction between 8B and Σ- prepares a shallow atomic bound state with a narrow conversion width. The coupling of strong interaction between the two states (8B + Σ-) and (8Be*+ Σ0) pushes down the energy of resonance state and it is expected to reproduce the correct energy position and level width of the second peak of the observed 9ΣBe hypernuclear spectrum.

Protonium annihilation into two pseudoscalar mesons

The annihilation of a p p atomic bound state into a pseudoscalar meson and its antiparticle is analyzed in terms of threshold values of the helicity amplitudes for the basic annihilation process p p → m m . Parity and angular momentum conservation restrict such decays to the 3L J states having J = L ± 1. In addition, apart from annihilation from the 3P 0 state, the threshold behaviour of the helicity amplitudes heavily suppresses this decay mode in the case of the 3L J states having J = L − 1. Simple expressions for the partial widths, total widths and branching ratios are derived. The branching ratios are independent of the principal quantum number but depend on the angular momentum quantum numbers. Measurement of the angular distribution of one of the mesons with respect to the X-ray emitted in the transition leading to the decaying 2P atomic state enables separation of the amplitudes for the decays of the 3P 0 and 3P 2 states. Polarization of the initially captured proton may provide otherwise inaccessible information about the dynamical evolution of the protonium atomic system during the cascade down from the state into which the antiproton is initially captured.

ATOMIC ENHANCEMENTS IN THE DETECTION OF AXIONS

Proposed bolometric and supercolloidal detectors can measure energy depositions of the order of atomic energies. At these energies, atomic bound state effects lead to great enhancements in the detection of absorbable weakly interacting particles. In this paper we compute these enhancements taking into account all Coulomb effects for nonrelativistic electrons. As an example, we show that solar axions could give event rates 104−105 times larger than published neutrino detector design capabilities. Thus, relatively small detectors might see solar axions.

Atomic enhancements in the detection of weakly interacting particles

Proposed holometric and supercolloidal detectors can measure energy depositions of the order of atomic energies. At these energies, atomic bound state effects lead to great enhancements in the detection of weakly interacting particles. As an example, we show that solar axions could give event rates 10 5–10 6 times larger than published neutrino detector design capabilities. Thus, relatively small detectors might see solar axions.

Determination via classical mechanics of the maximum number of electrons in an atomic bound state.

Let \ensuremath{\psi} be any normalizable energy eigenfunction for N electrons in an atom having Z protons in a fixed pointlike nucleus. Recently, it has been shown with use of quantum mechanics [Phys. Rev. Lett. 53, 907 (1984)] that, for the state \ensuremath{\psi}, N+1 with F no larger than 4. Evidence was presented that F=F(N)\ensuremath{\rightarrow}2 as N\ensuremath{\rightarrow}\ensuremath{\infty}. In this paper we show that the same result holds in classical mechanics for a bound system.

Maximum Number of Electrons in an Atomic Bound State

Let $\ensuremath{\psi}$ be any normalizable energy eigenfunction for $N$ electrons in an atom having $Z$ protons in a fixed pointlike nucleus. It is shown that, for the state $\ensuremath{\psi}$, $N$ and $Z$ are rigorously related by $N<FZ+1$ with $F=4$. This is independent of any statistics. Evidence is presented that the result can be improved in the sense that $F=F(N)\ensuremath{\rightarrow}2$ for $N\ensuremath{\rightarrow}\ensuremath{\infty}$. A comparison is made with a recent result of Lieb.

Relativistic R-matrix theory of photoionisation: application to neon

The R-matrix theory of atomic photoionisation using the Dirac Hamiltonian is formulated in a similar way to that used in the non-relativistic case. Both the initial atomic bound state and the final atomic continuum state are expanded in terms of R-matrix bases. The method is programmed for a general atomic system and then used to calculate the total photoionisation cross sections of ground-state neon atoms.

A Direct Measurement of the Collisional Population and Depopulation Rates for the N = 2 State of Atomic Hydrogen

A technique is described in which a plasma is prepared using a tunable laser such that the population of only a single atomic bound state differs significantly from its equilibrium value. Subsequent observation of the relaxation of this single state in the absence of laser irradiation and with all other levels close to their equilibrium populations then yields unambiguous values for the collisional depopulation and re-population rates for the level, free from uncertainties present e.g. in laser-induced fluorescence experiments.Results will be presented for the n = 2 state of hydrogen, but the technique is applicable to many first excited states in plasmas which need not be in either LTE or pure coronal equilibrium.

The atomic bound state of two pions and the π π scattering lengths

An upper bound for the low energy production rate of π+ π− atomic bound states in NN collisions is obtained and used to investigate the feasibility of taking π π scattering lengths from the X rays of this system.

R-matrix theory of photoionization. Application to neon and argon

The R-matrix method, which has been used recently to calculate electron-atom and ion collision cross sections and atomic polarizabilities is extended to enable atomic photoionization processes to be studied. Both the initial atomic bound state and the final atomic continuum state are expanded in terms of R-matrix bases. The method is programmed for a general atomic system and then used to calculate the photoionization cross sections of ground state neon and argon atoms leaving the residual ions in their ground or first excited states. Good agreement is obtained with recent experiments using synchrotron radiation both in resonant and non-resonant regions, showing that the method has a wide range of applicability.