The dipole operator for exotic atoms and molecules

This note clarifies the role of the Fried-Martin factor in the calculation of dipole matrix elements for transitions between muonic and hardronic states. Formulae are given which are appropriate for exotic atoms or molecules and which take account of screening.     

Laser spectroscopy of atoms in superfluid helium for the measurement of nuclear spins and electromagnetic moments of radioactive atoms

A new laser spectroscopic method named “OROCHI (Optical RI-atom Observation in Condensed Helium as Ion catcher)” has been developed for deriving the nuclear spins and electromagnetic moments of low-yield exotic nuclei. In this method, we observe atomic Zeeman and hyperfine structures using laser-radio-frequency/microwave double-resonance spectroscopy. In our previous works, double-resonance spectroscopy was performed successfully with laser-sputtered stable atoms including non-alkali Au atoms as well as alkali Rb and Cs atoms. Following these works, measurements with ^84?87Rb energetic ion beams were carried out in the RIKEN projectile fragment separator (RIPS). In this paper, we report the present status of OROCHI and discuss its feasibility, especially for low-yield nuclei such as unstable Au isotopes.     

Accurate determination of the scattering length of metastable helium atoms using dark resonances between atoms and exotic molecules

We present a new measurement of the s-wave scattering length a of spin-polarized helium atoms in the 2(3)S1 metastable state. Using two-photon photoassociation spectroscopy and dark resonances, we measure the energy E(nu)=14= -91.35+/- 0.06 MHz of the least-bound state nu = 14 in the interaction potential of the two atoms. We deduce a value of a=7.512+/-0.005 nm, which is at least 100 times more precise than the best previous determinations and is in disagreement with some of them. This experiment also demonstrates the possibility to create exotic molecules binding two metastable atoms with a lifetime of the order of 1 micros.     

Hyperfine structure of light exotic atoms

Recoil corrections to the hyperfine structure of light exotic atoms, including the effect of the anomalous magnetic moment are calculated for light muonic and baryonic atoms. In the case of muonic atoms, the effects of recoil and finite nuclear size are significant in view of the presently attainable experimental precision.     

On the formation of exotic atoms

A general disagreement exists between theory and experiment in the field of formation and decay of muonic and pionic atoms. Allowing for collisional processes in the deexcitation of heavy exotic atoms can substantially change the interpretation of experimental Coulomb-capture ratios, particularly of those measured by the muonic X-ray method.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.The author is grateful to Prof. F. Measday (Univ. of British Columbia, Vancouver, Canada) and Dr. J. Révai (C. R. I. P., Budapest) for illuminating discussions.     

Current electric quadrupole moments of atoms and nuclei

It is shown that current electric multipoles exist. Their field is electrostatic and it is unrelated to the existence of a net electric charge. At long range, it is the same as the field of the corresponding charge electric multipoles. Current electric multipoles arise during the motion of magnetic multipoles. An orbital motion of magnetic dipoles, a precession of a current-carrying loop, and the motion of magnetic quadrupoles all lead to current electric quadrupole moments. Expressions for the current electric quadrupole moments of atoms and nuclei are derived.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 53–58, July, 1991.The author wishes to thank S. A. Kuten' and V. I. Rapoport for useful comments offered during the writing of this paper and for a discussion of the results.     

Scattering of light exotic atoms in excited states

The differential and total cross-sections for the scattering of muonic, pionic, kaonic and antiprotonic hydrogen in excited states from atomic hydrogen have been calculated for the purpose of atomic cascade calculations. The scattering problem is treated in a fully quantum mechanical framework which takes the energy shifts and, in the case of the hadronic atoms, the widths of the ns states into account. The validity of semiclassical approximations is critically examined. Received 4 December 2001 and Received in final form 4 February 2002     

Differential elastic cross-sections of excited exotic hydrogen atoms

Differential cross-sections for the elastic scattering of excited exotic hydrogen atoms by hydrogenic atoms are calculated for the first time. The calculations are performed for exotic atoms (μ a,π a; a=p,d,t) in the states with the principal quantum numbers n=2-10 at relative motion energies E=0.001-15 eV and at scattering angles ϑ =0–180^00B0;. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of Debye plasma on compressed exotic atoms

The effect of plasma environment on the energy levels and structural properties of exotic atomic systems p⁺μ⁻ and μ⁺μ⁻ bound by Coulomb force and confined at the centre of an impenetrable spherical box has been thoroughly studied. The plasma environment is assumed to produce a Debye type of screening in the potential energy. Compression is generated by confining the exotic system in a spherical box. The effect of plasma and compression on system properties like orbital energies, excited states, dipole polarizabilities, oscillator strength and transition probabilities has been studied using time dependent variation perturbation theory. Ionisation pressures at different plasma screening have been estimated. The data obtained may be useful in the astrophysical context where different plasma environments exist.     

Experiments with exotic atoms and exotic nuclei at GSI, recent developments and future prospects

Results and new developments with exotic atoms and exotic nuclei are presented from recent experiments at GSI. The proposed European inflight facility at GSI will open up new fields of outstanding research and will simultaneously access unknown regions of nuclei with new properties. A new generation of precision experiments will be performed with stored exotic nuclei, whereby nuclear reactions with an internal target and electron scattering in a small electron-ion collider will be a great challenge.     

Hadronic atoms and ticklish nuclei: The E2 nuclear resonance effect

The E2 nuclear resonance effect in hadronic atoms offers a way to increase the hadronic information that can be obtained from hadronic X-ray experiments. The effect occurs when an atomic deexcitation energy closely matches a nuclear excitation energy, so that some configuration mixing occurs. It shows up as an attenuation of some of the hadronic X-ray lines from a resonant versus a normal isotope target. A number of promising cases for ifπ^?, K^?, p?, and Σ^? atoms are discussed and a spectacular and potentially very informative experiment on p?-¹⁰⁰Mo is proposed.     

Decoupling and coherence in E1 and E2 moments in drip line nuclei

I discuss first the effect of decoupling of extended wave functions and the coherence in the low-energy E1 strength in drip line nuclei ¹²Be and ¹³O, which are studied by large-scale shell model calculations including 3 ?ω configuration space. The calculated results are compared to recent experimental data of Coulomb excitations. The quenching of the core polarization charges in drip line nuclei is also discussed in relation to recent observations of quadrupole moments in B-isotopes. Received: 1 May 2001 / Accepted: 4 December 2001     

Formation of fast exotic atoms by radiative Coulomb capture

Interesting surprises in some exotic atom kinetics have been reported recently. These involve muonic atom transfer cross sections, nuclear pion capture and theq 1s effect in CF. These can be explained if the exotic atom population contains a contributing fast component. Such fast atoms can be formed by radiative continuum to bound transitions of fast (keV) muons or pions. Cross sections for formation of such fast pionic and muonic atoms and their velocity distributions are reported. The possibility of these processes competing with the thermalisation channels and contributing effectively to the exotic atom population is discussed.     

Recoil corrections to the hyperfine splitting of exotic atoms

All recoil corrections to the hyperfine structure to orderα ⁴ are given, for arbitrary nuclear spins.     

On the interaction of exotic atoms with their environment

A theoretical study is made of the effect of collisions on the two-photon 2s → 1s transition of the fully-ionized muonic boron migrating in helium. Data on atomic processes are indicated which may be extracted from measurements of the yield of this transition. This revised version was published online in August 2006 with corrections to the Cover Date.     

E2 moments andg-factors in neutron deficient lead isotopes

The half-lives of the (vi _13/2)² I ^π=12⁺ isomers in^{190, 192}pb were measured asT _1/2 =7.9(4) μs and 1.10(5) μs, respectively. The quadrupole moment and theg-factor of the corresponding state in¹⁹⁴Pb were determined toQ=49(3) efm² andg=?0.167(2) using the perturbed angular distribution method. Additionalg-factor and lifetime information was obtained for a number of isomers in^{194, 195, 196, 197, 198, 199, 200}Pb also involvingi _13/2 neutrons. The results are discussed in comparison to a two-quasiparticle Tamm-Dancoff calculation in the full shell using the surface delta interaction.     

High-velocity components in exotic atoms,their origin and effects

The evolution of the kinetic energy distribution during the cascade is shown to play an important role for pionic and muonic atoms in hydrogen and deuterium. The kinetics of muon transfer in excited states is studied with a new cascade code and the results are compared with recent experimental data.