Studies of the positive muon behavior in solid H2 and D2

Using a pulsed muon beam, we have investigated the microscopic μ⁺ behavior in solid H₂ and D₂ down to 0.6 K by the μ⁺SR method. From the studies of μ⁺ spin relaxation phenomena in solid para‐ H₂ and ortho‐ D₂, we have found that μ⁺ forms three distinct microscopic states; H₂μ⁺( D₂μ⁺)(20\sim25\%), muonium (15\sim20\%) and μ⁺(\sim60\%). In H₂μ⁺, the μ⁺ spin is depolarized in solid para‐ H₂ and a local magnetic field B_loc=1\sim2 G is deduced from LF‐μ⁺SR measurements. The magnitude of B_loc is inconsistent with the magnetic dipolar field (\sim25 G) expected from the magnetic moments of two protons in the H₂μ⁺ molecule and suggests that the H₂μ⁺ molecule might be in the rotationally excited state. From LF‐μ⁺SR measurements, muonium and μ⁺ have been found to diffuse in solid o‐ D_2. The diffusion rate of muonium is two order of magnitude larger than that of μ⁺. This revised version was published online in August 2006 with corrections to the Cover Date.     

Muonium desorption to vacuum from hot iridium surface

Slow muonium (Mu) emission from the surface of iridium (Ir) foil has been observed in vacuum above \sim1200\ K with a yield of 5(1)% Mu per incident muon stopped in the foil. The relative Mu signal was found to be thermally activated with E_a=1.86(1)\ eV. Analysis of the time‐differential evolution of Mu in vacuum at T_Ir=1580\ K showed that the trapping rate of positive muons during diffusion in the bulk Ir was nearly zero. In situ measurements of the surface of Ir with X‐ray photoelectron spectroscopy verified that the main source of impurities in the 99.9%‐Ir was molybdenum (Mo). This revised version was published online in August 2006 with corrections to the Cover Date.     

Stability of two-dimensional crystalline aggregates of a protein studied by molecular dynamics

Two-dimensional protein (ferritin) aggregates with a square lattice symmetry, which were formed within a thin liquid layer on a mercury surface, were studied by molecular dynamics (MD) simulation. For the simulation, the ferritin molecule was modeled by an assembly of 49 spheres, and the intermolecular interactions were given by simple formulae. During the simulation, molecules were confined within a layer, which corresponds to the thin liquid layer. An annealing MD simulation was done starting from a random molecular configuration within the layer, and aggregates with the square lattice symmetry were also obtained. To study the stability of aggregates, dissociation processes of the aggregates were analyzed using MD simulations at room temperature. Interactions between the nearest-neighbor molecules were regarded as bonds. Mean bond energies and correlation coefficients between the bond energies were calculated from the MD trajectories. A decay profile according to the dissociation was obtained, yielding a dissociation rate constant. Buried bonds were stronger than peripheral bonds. The larger the aggregate size, the stronger the bond for each of the buried and peripheral bonds. A simple theoretical account, which is applicable to a general bonded network, was introduced to analyze the dynamics of the aggregates. © 1994 by John Wiley & Sons, Inc.     

Syntheses of 10-oxo, 10 alpha-hydroxy, and 10 beta-hydroxy derivatives of a potent kappa-opioid receptor agonist, TRK-820

Syntheses of 10-oxo, 10alpha-hydroxy, and 10beta-hydroxy derivatives of a potent kappa-opioid receptor selective agonist, TRK-820, are described. These derivatives were supposed to be potential degradation products in formulation of TRK-820 as a result of autoxidation. 10-Oxo-TRK-820 11 was derived from 10-oxo-4,5-epoxymorphinan 14 in 10 steps in 32% overall yield. Reduction of the 10-oxo group in 4,5-epoxymorphinan with NaBH(4) gave 10beta-hydroxy-4,5-epoxymorphinan, exclusively. A stepwise inversion method of the 10beta-hydroxy group to produce 10alpha-hydroxy-4,5-epoxymorphinan was established. By HPLC analyses, 10alpha-hydroxy-TRK-820 12 was confirmed to be one of the degradation products in developing formulation of TRK-820.     

μ+SR study of two-dimensional antiferromagnets,delafossite-type compounds

⁺SR experiments were performed on delafossite-type compounds, CuCrO₂, AgCrO₂, CuFeO₂, which are model compounds of triangular lattice antiferromagnets. The initial asymmetries are much smaller than the expected value, implying muonium formation. The time spectra are composed of slow andfast relaxation components. We attributed the components to signals from ⁺ stopped at the center of O^2– ions andmuonium far from nuclear dipole moments, respectively. The asymmetries decrease belowT _N but no precession spectra were observed. Relaxation rates of slow andfast relaxation components show maxima atT _N.     

Anisotropic paramagnetic shift of μ−O in the highT c related materials LaSrCuO and LaCuO

The negative muon (^–) was used as a microscopic probe for the study of the electronic state at the oxygen site in highT _c related LaSrCuO materials. Using good single crystals, two types of signals are obtained corresponding to two different oxygen sites: one highly anisotropic, which shows a large (order of 1%) shift under the magnetic field inc-axis direction, the other less anisotropic and with a smaller amplitude (order of 0.2%). These results of ^–OSR show quit a difference with the result of¹⁷O-NMR, where the paramagnetic shift has axial symmetry along the Cu-O bond direction and a magnitude of the order of 0.2% and 0.05%.     

Location and associated hyperfine properties of μ+ in La2CuO4

The location of the positive muon used as a probe in highT _c systems is investigated using the unrestricted Hartree-Fock cluster procedure. Our calculations indicate that ⁺ is located in thea–c plane at a distance of 1.08 Å from the apical oxygen at a ⁺-O(a)-Cu angle of 25°. The hyperfine field at this site is also calculated. Our results show the importance of including the local contact and dipolar contributions to the hyperfine field which arise from the unpaired electron spin distribution in the vicinity of the muon.     

Slow and monoenergetic (3Heμ−)+ beam production and novel applications

Based upon the recent discovery at UT MSL/KEK, a new idea is proposed for producing a slow and monoenergetic (3.2 keV) (³He^–)⁺ ion beam by using particle decay of the (d³He) muon molecule formed during the (d) to³He transfer reaction. The proposed intense (³He) beam as well as the less intense (⁴He) beam will open up way to various new types of important CF experiments.