Nuclear auger effect in muonic atoms

In a muonic atom electromagnetic transitions proceed via emission of X-rays, electrons from the atomic cloud (Auger electrons), or neutrons from the nucleus (nuclear Auger effect). We calculate the neutron spectrum for muonic ²⁰⁷Pb and ²⁰⁹Bi within a microscopic theory of nuclear reactions. The compound nucleus mechanism is dominant. Most of the neutrons arise from the E2 transition 3d → 1s. Agreement between experiment and calculation is achieved to within a factor of 2.     

Difference in the electronic and fission decay modes for muonic atoms

A simple model is presented which predicts a difference in the electronic and fission decays of ground-state muonic heavy atoms. It is interpretable in terms of the relative population of two nuclear states: the isomeric fission state and the ground state. The application of the model to ²³⁸U indicates there could be a significant population of the isomeric state at the end of the muonic atomic cascade.     

Measurement of isotope shift and hyperfine splitting of190, 191, 193, 197Pb isotopes by collinear laser spectroscopy

We report here on the measurement of isotope shift and hyperfine splitting of^{190, 191, 193, 197}Pb for the 723 nm atomic optical transition. Detailed analysis of the optical data has been done by combining them with the available muonic and electronicx-ray isotope shift data. The magnetic dipole moments and the electric quadrupole moments of the odd isotopes have been extracted from the hyperfine coupling constants of the atomic states involved in the optical transition used.     

Muonic atoms spectroscopy

A review is given of the physics of muonic atoms. The results of spectroscopic experiments on μ⁻ atomic systems are discussed. Special emphasis is given to the determination of nuclear charge moments, the nuclear polarization correction, and QED corrections.     

μ −SR-Spectroscopy on light neutral muonic atoms

In the past few years ^–SR-spectroscopy has been successfully applied to the simple muonic atoms, namely muonic helium: He ^–e^–. Here the theoretical and experimental progress in understanding this atomic system consisting of a nucleus, a muon and an electron is reviewed. The various effects contributing to the ground state hyperfine structure are explained. The experiments are described and are compared with the theoretical calculations.     

Dynamics of muonic atom cascade in hydrogen-helium mixtures

The deexcitation of excited muonic protium and deuterium in the mixture of hydrogen and helium isotopes is considered. Methods of experimental determination of the probability of direct atomic muon capture by hydrogen and muon transfer rates from excited muonic hydrogen to helium are proposed. Theoretical results for the population of the muonic atoms in the ground state, , are compared with the existing experimental data. Results obtained for mixtures are of interest for investigation of nuclear fusion in muonic molecules. Received: 6 August 1998 / Revised: 1st October 1998 / Accepted: 2 October 1998     

Recent Advances in the Theoretical Methods and Computational Schemes for Investigations of Resonances in Few-Body Atomic Systems

This paper describes the research works performed in my group in recent years in the theoretical methods and computational schemes for investigations of resonances in few-body atomic systems. These methods include the complex absorbing potential method, the stabilization method, and the method of complex scaling. In addition to atomic resonances, this paper also describes some of our recent works on investigations of Borromean bindings in three-body atomic systems. By systematically changing the two-body interaction from the long range Coulomb potential to the short range screened Coulomb (Yukawa) potential, we have investigated the Borromean bindings for hydrogen molecule ion H ₂ ⁺ and the muonic molecular ions.     

Prompt γ-rays from Pb following neutron emission from muonic Pb

We have measured the energies and intensities of prompt γ-rays from ²⁰⁶Pb that follow neutron emission from muonic ²⁰⁷Pb. For the levels at 803, 1704 and 2648 keV we deduce muonic isomer shifts. By comparing the relative and absolute yields of the γ-rays with the intensities of neutron groups observed in (γ, n) reactions, we find that roughly 50% of the prompt neutrons from muonic ²⁰⁷Pb result from radiationless deexcitation of atomic levels with .     

Fission of muonic 232Th and 239Pu

The neutron emission is studied following the formation of muonic atoms of ²³²Th and ²³⁹Pu. Energy and time distributions are measured. Various processes which contribute to the measured spectra are considered. A collective resonance model of the muon capture is used to calculate the nuclear excitation function. The probability of the radiationless nuclear excitations and the influence of the presence of the bound atomic muon on the fission barrier are discussed. The existing data for the $\text{Γ}{}_{\mathrm{n}}\text{Γ}{}_{\mathrm{f}}$, are analysed. As a result of the analysis the rates of the prompt and delayed fission events (due to the radiationless mu-atomic transitions and the nuclear muon capture, respectively) are deduced from the experimental data to be 0.006/muon and 0.045/muon for ²³²Th and 0.10/muon and 0.49/muon for ²³⁹Pu, respectively. The increase of the fission barrier for muonic atoms is confirmed. The experimental neutron rates can be consistently explained only if it is assumed that in both nucleides the K_α radiationless transitions do not induce fission. The increase of the fission barrier for ²³⁹Pu is hence deduced to be not less than 1.2 MeV. The fate of the atomic muon after the nuclear fission is briefly discussed. Its influence on the interpretation of the present results is found to be small.     

Radiationless 3d→1s transition in muonic atoms of 238U

The probability of the radiationless muonic transition 3d→1s in ²³⁸U has been determined. This was done by comparing the singles muonic spectrum with the one gated by the 2p→1s transition. The probability was found to be (14±5)%.     

Generation of cw 243 nm radiation and application to laser spectroscopy of the strontium isotopes

Intra-cavity second harmonic generation in a ring dye laser using lithium formate monohydrate has been observed to produce tunable cw UV radiation around 243 nm with single frequency powers of up to 1.4 mW. This wavelength region is of particular interest in the context of Doppler-free spectroscopy of atomic hydrogen. The radiation was used to excite an atomic beam of strontium to study the transition 5s^{2 1}S₀-4d5p ¹P₁ of Sr I. The isotope shifts were determined as follows: ⁸⁸Sr-⁸⁷Sr 123.7(8) MHz; ⁸⁸Sr 285.0(8) MHz; ⁸⁸Sr-⁸⁴Sr 600.1(9) MHz. The values are compared with results for other lines and muonic isotope shifts to obtain the specific mass shift and field shift in this transition and to study the configuration mixing effects. The hyperfine structure of ⁸⁷Sr was not resolved, the intervals being very much less than the measured linewidth of 25 MHz.     

Muonic molecules in superintense laser fields

We study theoretically the ionization and dissociation of muonic molecular ions (e.g., dd mu) in superintense laser fields. We predict that the bond breaks by tunneling of the lightest ion through a bond-softened barrier at intensity I > or =10(21) W/cm(2). Ionization of the muonic atomic fragment occurs at much higher intensity I > or =6 x 10(22) W/cm(2). Since the field controls the ion trajectory after dissociation, it forces recollision of a approximately 10(5)-10(6) eV ion with the muonic atom. Recollision can trigger a nuclear reaction with sub-laser-cycle precision. In general, molecules can serve as precursors for laser control of nuclear processes.     

Non-axiality effects in quadrupole hyperfine splitting in muonic 238U

The quadrupole hyperfine splitting in muonic atoms with nuclei having non-axial symmetry is calculated within the rigid asymmetric rotor model. The X-rays emitted in 4F-3D and 3D-2D transitions of muonic ²³⁸U were measured with high resolution and an analysis of the spectrum was performed to find the quadrupole deformation parameters β and γ.     

Collisional problems in the μCF cycle before muonic molecule formation

Important processes in the muon-catalyzed fusion cycle preceding muonic molecule formation are discussed. These include muonic atom formation as well as the subsequent elastic, isotopic-exchange, and hyperfine-state quenching collisions of the muonic atoms. Modern methods for atomic capture of the negative muon are reviewed. Elastic and inelastic cross sections obtained in the improved adiabatic representation are given, and rates at liquidhydrogen density are tabulated for easy reference and comparison.     

Laser polarized muonic atoms

Lasers are an important tool in the field of muon physics. A new application of lasers, namely producing polarized muonic atoms, is the subject of a new program at LAMPF. One technique already demonstrated is stopping unpolarized muons in a laser polarized³He target. A more promising idea is to polarize neutral muonic helium by collisions with laser polrized Rb vapor. These methods for producing polarized muonic helium will be useful for measuring the spin dependence of nuclear muon capture and for determining the induced pseudoscalar coupling.     

Hadronic vacuum polarization correction in muonic atoms

The contribution of hadronic vacuum polarization to the energy levels of muonic atoms is reevaluated using an improved parametrization of the total cross section for e⁺ e^?→hadrons. The numerical results can be simply related to the correction due to muonic vacuum polarization.     

Intensitätsmessung von Röntgen- und Kerngammastrahlung an einigen schweren Myonenatomen

Absolute intensities of the 5–4 muonic X-ray transition in muonic W, Os, and Bi, and relative intensities of other X-ray transitions have been measured and compared with cascade calculations. The excitation of several levels in W, Os, Ir, Tl, and Bi nuclei resulting from the muonic cascade process has been observed and absolute excitation probabilities have been determined. For the first 2⁺ level of¹⁸⁸Os and the first 3/2⁺-levels of^203,205Tl the excitation probabilities are larger than calculated. The results are discussed.     

Electro-weak interaction in muonic atoms

The parity non-conserving effective neutral current interaction between charged leptons and nucleons is studied in its implications for atomic physics. Present results on heavy electronic atoms are discussed within the standard electroweak theory and beyond. The new features provided by muonic atoms open the way to the nuclear-spin-dependent parity non-conserving effects. Different observables proposed to study these effects in muonic atoms are reviewed.     

Isotope shift in the Ca I resonance line and changes in mean-square nuclear charge radii of the stable Ca isotopes

The isotope shift of all stable Ca isotopes was studied in the Ca I resonance line. Enriched isotopes were used in an atomic beam, passing through the center of a spherical Fabry-Perot interferometer. The measured isotope shifts were separated into mass shift and field shift by comparing the optical isotope shift with δ〈r ²〉 values derived from recent muonic x-ray measurements. The results are discussed together with known data on the isotope shift in the Ca I intercombination line and data from Hartree-Fock calculations. The following mean values are obtained for the change in nuclear charge distribution δ〈r ²〉 [fm²]∶ [40, 42] 0.23(3); [40, 43] 0.13(3); [40, 44] 0.28(4); [40, 46] 0.14(7); [40, 48] 0.00(2).     

Nuclear excitation and isomer shifts in muonic atoms: (II). Model-independent parametrization and discussion

Excitation probabilities and isomer shifts for about 50 excited nuclear levels from muonic atoms of Sm, Gd, Eu, Tm, Yb, Ta, W, Re, Os, Ir, Pt, Hg, Tl, and Bi are discussed. The data for ¹⁵³Eu are used in comparison with isomer shifts from the Mössbauer technique to evaluate electron density differences in rare earth compounds. Mössbauer and muonic isomer shifts are sensitive to different moments of the change of the charge distribution. Therefore, from a comparison new information can be deduced. The results of the muonic isomer shifts are compared with calculations based on various nuclear models.