Calculation of the 3p-3d transitions in muonic helium

The energy splittings of the 3p and 3d states of muonic helium have been calculated. The theoretically predicted transition energies should be useful in connection with a proposed laser resonance experiment.     

Pionic x-ray transitions in 3He

Pionic ³He atoms have been produced in a gaseous target. Energies and strong absorption broadening of the 2 → 1 and the 3 → 1 transition lines have been measured. The 1s level is shifted by 44 ± 5 eV by the (attractive) strong interaction, and the natural 1s level width is 42 ± 14 eV.     

Nuclear charge radii from X-ray transitions in muonic atoms of carbon,nitrogen and oxygen

Energies of muonic X-rays of the K-series of carbon, nitrogen and oxygen have been measured with an accuracy of about 15 eV. Root mean square radii of the nuclear charge distributions were deduced. The results 2.49±0.05 fm for carbon, 2.55±0.03 fm for nitrogen and 2.71 ±0.02 fm for oxygen are in good agreement at comparable accuracy with recent electron scattering data.     

Pionic K X-rays in liquid He

Energies and lorentzian widths of pionic K X-ray transitions have been measured in liquid ³He with improved accuracy. The strong interaction on the π³He 1s level is found to be attractive and to produce an increase in the K transition energies of 34 ± 4 eV; the measured lorentzian width is 36 ±7 eV. Measured values are also presented for K X-ray energies in liquid π⁴He and μ⁴He, the lorentzian width of the 1s level in π⁴He, and relative intensities of K X-ray transitions in π³He, π⁴He and μ⁴He. The measurements are compared with those of others and with recent theoretical calculations.     

On the hyperfine structure of neutral muonic helium

The ground state hyperfine splitting of the neutral muonic helium atom has been (re)calculated to be equal to 4,493.3 Mhz.     

Excitation of deformation vibrations by radiationless muonic transitions

An investigation is carried out for selected doubly even nuclei in the rare-earth and actinide regions for possible resonances between pairs of muonic levels of the appropriate quantum numbers and certain nuclear collective states. Such resonances can lead to the excitation of the particular nuclear state involved, and could be used as an alternate means of nuclear excitation. Electric monopole excitations were found which can result in the excitation of the nuclear 0⁺ level of the β-band. The muonic states involved, however, are such that the probability of nuclear excitation may be small. An electric quadrupole resonance in ¹⁸²W involving the excitation of the 2⁺ state of the β-band is found to be a very likely candidate. Dipole and octupole resonances were also investigated; however no possible resonances were found. Also unsuccessful was the search for quadrupole excitations of the 2⁺ state in the γ-band. The matrix elements involved in the EO and E2 resonances are calculated, the nuclear contribution being computed using the nuclear collective model of Davydov and Chaban. The probability for nuclear excitation in the E2 resonance in ¹⁸²W is computed.     

The two-photon transition of the fully-ionized muonic boron migrating in helium

In recent experiments performed at the Paul Scherrer Institute (PSI) measurements were made of the yield of the two-photon transition of the fully-ionized muonic boron formed and quenched in a gaseous mixture of diborane B₂H₆ and helium. In the present work this yield is calculated for an idealized case of a very low diborane density when the main 2 s state decay modes competing with the two-photon transition are due to the electron transfer from helium to the μ-ion. As the rate of this transfer depends strongly on the relative velocity, a treatment is needed of the whole kinetics of processes occurring with the μ-ion in helium. Accordingly, within the optical model with a complex potential constructed before we calculate cross-sections of the elastic scattering and electron transfer. Then the time evolution of the μ-ion energy is considered and, finally, the yield is calculated. It proves that at helium pressures Torr this yield may be written in the form: ,where the factor C is greater than unity and increases rapidly with the initial energy E₀ which the μ-ion has after its formation in the diborane molecule. Thus measurement of the pressure dependence of allows E₀ to be estimated. The results obtained make it possible to suggest a similar parametrization of the PSI data. Received: 21 October 1997 / Revised: 16 January 1998 / Accepted: 2 March 1998     

μ-capture and ortho-para transitions in the muonic molecule ppμ

The capture of a muon by protons at different hydrogen densities is considered. More precise values of γ-factors for ortho- and para-states of the muonic molecule ppμ are obtained: 2γ_o = 1.009±0.001 and 2γ_p = 1.143±0.001. Relativistic effects are taken into account in the muonic molecule, and the rate of ortho-para transitions λ_op = (7.1±1.2) × 10⁴s^?1, caused by these effects, is calculated. With this value of λ_op the μ-capture rate in liquid hydrogen is found to be Λ_c = (490±10)s^?1 that is in agreement with the value Λ_c = 460±20 s^? recently measured by the Saclay-CERN-Bologna collaboration.     

Pionic transitions as tests of the connection between current and constituent quarks

A proposed connection between current and constituent quarks is discussed and tested through comparison with the magnitudes and signs of amplitudes for pionic transitions between hadrons.     

Absolute X-ray yields of light muonic atoms

The intensities of X-rays from muonic atoms formed in low pressure Ne, O₂, N₂, He, and H₂ gas was measured. For the pressure chosen external electron refilling can be neglected. Absolute yields were extracted and compared to results of cascade calculations. Knowledge of the yields of the circular X-ray transitions allows an in situ efficiency calibration of X-ray detectors down to energies of 1.5 keV. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase transitions of helium in aerogel

The effect of dilute quenched impurities on the liquid-vapor critical point, superfluid and He³?He⁴ phase separation transitions were studied by introducing liquid helium into aerogel. Aerogel is a highly porous glass consisting of atomically thin silica strands interconnected at random sites. In spite of the random environment, the transitions were found to be remarkably sharp and well defined. Although the silica network constitutes as little as two percent of the total volume, the nature of the transitions is completely changed. When a He³?He⁴ mixture is placed inside aerogel of 98 percent porosity, the coexistence region is found to be detached from the superfluid transition, line, giving rise to a new superfluid mixture that is rich in He³.     

Nuclear charge radii from muonic X-ray transitions in F,Na, Al,Si, P,S and K

Energies of muonic X-rays of the Lyman series of seven light natural elements (F, Na, Al, Si, P, S and K) have been determined with an accuracy of between 15 and 30 eV. Equivalent charge radii have been deduced. For μ^?-K, transitions to the 2s state allowed an additional constraint on the Fermi c-t diagram. The results are in good agreement with, and generally of an order of magnitude higher precision than, comparable electron scattering data.     

Measurement of muonic X-ray intensities and Coulomb capture ratios in chlorides

Muonic X-ray spectra of 32 chlorides have been measured with Ge detectors. Coulomb capture ratios and Lyman X-ray intensities were determined, and correlations to target data established. The experimental capture ratios agree well with the values from a recently proposed formula.     

One-photon two-electron transitions for metastable helium

We have obtained very accurate excitation energies for helium corresponding to the transitions 2p^{2 3}P^e ↦nln’l’ ³D^o using highly correlated Hylleraas-type wave functions. The doubly excited 2p^{2 3}P^e metastable bound state energy is obtained using Ritz variational principle. The upper bound of 2p^{2 3}P^e energy is –0.7105001556783 a.u., which is close to the best results –0.71050015567833 [R. Hilger et al., Chem. Phys. Lett. 262, 400 (1996)]. We employ complex-coordinate rotation method to obtain ³D^o resonances. The ³D^o resonance energies and widths along with one-photon two-electron transition energies are reported.     

Charged clusters in liquid helium

The appropriateness of the experimental study of charged clusters in liquid helium has been supported. The interaction potential of negative ions (electron bubbles) with inert clusters formed by Ne, Ar, Kr, and Xe atoms or H₂ and N₂ molecules has been found. Small clusters levitate at a distance of 13–16 Å above the negative ion. The scalings laws for the properties of charged inert clusters have been discovered and grounded; the number of quantum levels and states of such clusters has been determined. The mobility measurement of charged clusters may provide a new technique of probing the properties of impurity nanoparticles in helium.