Measurement of muon transfer rate λpt and molecular formation rate λppµ, in solid hydrogen targets,in solid hydrogen targets

The knowledge of muon transfer from protium to tritium is essentially theoretical and the different theoretical values disagree partially. Using solid hydrogen-tritium targets, with different tritium concentrations, we obtained precise experimental results for the transfer rate to tritium and the ppµ molecular formation rate. The time spectra of neutrons and alpha particles produced after dtµ fusion are used to determine the transfer rate _pt and the molecule formation rate _ppµ.     

Generation of the Ultracold Muonic Hydrogen Flux

We present the study of μp atom scattering in solid hydrogen. Anomalously large emission of E _pμ≤1.9 meV μp's from a solid H₂ layer was observed for the first time. This three times greater μp atom yield is due to non-elastic phonon scattering. As a result, it becomes possible to generate an ultracold flux of μp atoms. The recent calculations of the total and differential cross sections agree with all experimental results of μp atom scattering in solid H₂. This revised version was published online in August 2006 with corrections to the Cover Date.     

Resonant Scattering of Muonic Hydrogen Atoms and Dynamics of the Muonic Molecular Complex

Resonant scattering of muonic hydrogen atoms via back decay of the molecular complex, a key process in the understanding of epithermal muonic molecular formation, is analyzed. The limitations of the effective rate approximation are discussed and the importance of the explicit treatment of the back decay is stressed. An expression of the energy distribution for the back-decayed atoms is given. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ramsauer–Townsend Effect in Solid Hydrogen

The TRIUMF E742 experiment has measured the energy dependence of the scattering cross-sections of muonic deuterium and tritium on hydrogen molecules for collisions in the energy range 0.1–45 eV. The experimental setup permits the creation of muonic atom (μd or μt) beams. The multilayered target system gives the possibility to choose the type of interactions to study and to isolate a particular interaction. The scattering of μd or μt beams on H₂ is analyzed via the muon transfer reaction to neon. The time-of-flight method is used to measure the scattering cross section as a function of the energy of the muonic atom beam. The results are compared, using Monte Carlo simulations, with theoretical calculations which have been recently performed with high accuracy. This revised version was published online in August 2006 with corrections to the Cover Date.     

Kinetic energy of π− p-atoms in liquid and gaseous hydrogen

We have measured the Doppler broadening of neutron time-of-flight spectra from the reaction π⁻ p → π⁰ + n in atomic states. From the data, we infer that the kinetic energy distribution of π⁻ p-atoms in liquid and gaseous hydrogen contains discrete ‘high-energy’ components with energies as high as 200 eV attributed to Coulomb de-excitation. In liquid hydrogen, evidence for Coulomb de-excitation transitions with Δn = 2 has been found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Electronic structure and properties of isolectronically substituted compounds Y1Ba2−m M m Cu3O7 and Y1Ba2−m M m Cu4O8 (M=Be,Mg, Ca,Sr, Ba,Ra)

According to cluster calculations, the electronic structures of compounds based on Y₁Ba₂Cu₃O₇ and Y₁Ba₂Cu₄O₈ with isoelectronically substituted barium have some qualitative distinctions. These compounds behave differently upon barium substitution by other elements due to differences in the character of their highest occupied and lowest unoccupied molecular orbitals. Substitution of barium by radium is expected to lead to an increase in oxygen stability without a significant decrease in the critical temperature of superconduction transition T_s. In order to raise T_s, it is of interest to study the systems YBa_2−m(Be or Mg)_mCu₃O_x and YBa_2−m(Ca, Sr)_mCu₃O_x. On partial substitution of barium by calcium in YBa₂Cu₄O₈, the mechanism of T_s elevation may involve contraction of the forbidden band due to oxygen sublattice distortions in the vicinity of Ba centers. D. I. Mendeleev Russian Chemical Engineering University, Novomoskovsk Branch. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 2, pp. 24–31, March–April, 1994. Translated by O. Kharlamova     

New precision measurements of dµd fusion

A new experiment was started at PSI aiming for high-precision and complete studies of dµd fusion in D₂, HD and D₂/H₂ gas mixtures. A high-pressure ionization chamber surrounded by a set of neutron counters is used to observe dd-fusion at temperatures between 25 and 350 K. Here we report preliminary results from the first test run with pure D₂ filling.     

Collisional deexcitation of exotic hydrogen atoms in highly excited states

The deexcitation of exotic hydrogen atoms in highly excited states in collisions with hydrogen molecules has been studied using the classical-trajectory Monte Carlo method. The Coulomb transitions with large change of principal quantum number n have been found to be the dominant collisional deexcitation mechanism at high n. The molecular structure of the hydrogen target is shown to be essential for the dominance of transitions with large Δn. The external Auger effect has been studied in the eikonal approximation. The resulting partial wave cross-sections are consistent with unitarity and provide a more reliable input for cascade calculations than the previously used Born approximation. Received 28 May 2002 Published online 15 October 2002 RID="a" ID="a"e-mail: thomas@physik.unizh.ch