μ+ diffusion in copper studied by zero field μSR

Diffusion of muons in high purity Cu was studied by the zero-fieldSR method at temperatures from 134 K down to 0.09 K. The experimental data show clear evidence that the muons still diffuse below 15 K; the measured diffusion rate has a minimum at around 15 K and seems to become independent of temperature below about 0.5 K.     

Zero fieldμ + spin relaxation in some REAl2 intermetallics

Transverse field measurements on the rare-earths intermetallics REAl₂ in their paramagnetic regime have previously been carried out [1]. To aid discrimination between inhomogeneous line broadening and RE fluctuations which both contribute to the damping of the transverseSR pattern, we have carried out zero field measurements on three selected compounds (PrAl₂, GdAl₂, DyAl₂) between 300 and 25 K. A small longitudinal decoupling field (6 mT) was applied in some cases. The present data corroborate the findings of the transverse field study: The polarization rate increases rapidly when approaching magnetic order. The high temperature limit of the spin fluctuation rate is markedly different in the three compounds. The ⁺ diffuses rapidly in all REAl₂ compounds.     

μ + Residual polarization in water,CS2, C6F6 and hydrocarbons under strong decoupling fields

The ⁺ decay asymmetry was measured as a function of longitudinal magnetic field (LF) between zero and 10 kG in spin decoupling experiments on muons in water, c-hexane, CS₂, C₆F₆, C₆H₆ etc. The results were compared both with the diamagnetic polarization,P _D, measured by transverse-field (TF) experiments ⁺SR, and with the asymmetry observed in ⁺ spin resonance experiments under longitudinal field. These results have been interpreted in terms of spin conversion and chemical reactions of muonium (Mu) with paramagnetic species such as free radicals in the muon track or spur. It is argued that spin-conversion reactions are responsible for the so-called missing fraction of ⁺ polarization in various media.     

Comparative pharmacokinetics of acetohexamide and its metabolite, hydroxyhexamide in laboratory animals

The pharmacokinetic profiles of the hypoglycemic agent, acetohexamide (AH) and its major active metabolite, hydroxyhexamide (HH) were studied in three species of laboratory animals after intraperitoneal (ipl) administration in comparison with those after intravenous (iv) administration of AH and of the preformed metabolite HH. Reductive biotransformation of AH to HH was reversible in rats and guinea pigs, while it was irreversible in rabbits. The parameters of reversible drug-metabolite pharmacokinetics were calculated, including essential clearances of reversible and irreversible elimination, volumes of distribution at the steady state and sojourn times or turnover rates of the metabolite pair. An interconversion model, which incorporated a first-pass metabolism, was applied to the disposition kinetics of AH and HH, and the available fractions of AH and generated metabolite HH in each species were elucidated.     

Reductive dimerization of alkylidenemalonates using samarium(II) diiodide and 1H-NMR behavior of the dimers, 2,3-diaryl-1,1,4,4-butanetetracarboxylates

Alkylidenemalonates were readily dimerized in the presence of SmI2 to give 2,3-disubstituted 1,1,4,4-butanetetracarboxylates as mixtures of meso and racemic isomers in moderate to good yields. The structure of the less polar isomer of tetraethyl 2,3-diphenyl-1,1,4,4-butanetetracarboxylate was determined by X-ray crystallographic analysis to be the meso form. Characteristic 1H-NMR behavior of the meso and racemic isomers is also discussed.     

Recent Result of Muon Catalyzed t–t Fusion at RIKEN-RAL

We have measured X-rays and neutrons associated with the muon catalyzed t–t fusion process at the RIKEN-RAL Muon facility. In the X-ray measurement, we observed K_α and K_β X-rays originating from the muon sticking process in muon catalyzed t–t fusion, and obtained the K_α X-ray yield and the K_β/K_α intensity ratio. An average recoil energy of the (μ⁻α) atoms in a solid T₂ medium was determined from the observed Doppler broadening width of the K_α X-ray line. The obtained t–t fusion neutron has shown an exponential time spectrum with a single component and a continuous energy spectrum with a maximum energy of 9 MeV. We have determined the t–t fusion neutron yield, the t–t fusion cycling rate and the muon sticking probability from the neutron data. The obtained maximum neutron energy is a very peculiar value from the view point of the reaction Q value (11.33 MeV) with the three-particle decay mode at the exit channel: t + t → α + n + n + Q. The obtained neutron energy distribution was analyzed by a simple model with two neutron energy components; reasonable agreement has been obtained, suggesting a strong (n–α) correlation in the exit channel of the t–t muon catalyzed fusion reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of the Cosmic-Ray Muon Detection System for Probing Internal-Structure of a Volcano

Very high-energy cosmic-ray muons penetrating through a mountain enable us to probe the internal structure of volcanoes. An improved cosmic-ray muon detection system comprising two segmented detectors with multiplicity cut of the soft components of cosmic rays was developed. The test measurement for the volcano Mt. Asama is described. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ab Initio Investigation of Helium Bubble Formation from Trapped He+ Ions in Solid Hydrogen

We are involved in a program aimed at a first-principles examination of the possibility of helium bubble formation in solid hydrogen. Our procedure is based on an extension of the Hartree–Fock cluster approach that we have been using for study of individual He⁺ ions in solid hydrogen. The preliminary results of our cluster investigations of a particular configuration of two He⁺ ions in neighboring tetrahedral interstitial positions are presented here. It has been found that the hydrogen molecules common to the two He⁺ ions lead to a substantial attractive force between the ions that almost overcomes their inherent repulsion, leading to a binding energy for this configuration only slightly less than the binding energy for two well separated trapped He⁺ ions. The analysis of our results have suggested future investigations of different pairs of trapping sites which appear to be more favorable for providing higher binding energies for the He⁺ pairs. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Precise Measurement of the μ+ Lifetime

The lifetime of the positive muon (τ_μ ⁺) can be directly associated with the Fermi Coupling Constant (G _F ), which is one of the most basic parameters of the Standard Model. However, the current experimental accuracy of the τ_μ ⁺ is ∼30 ppm and it has not been improved for more than 15 years. We propose a new experiment for a pulsed muon facility such as RIKEN-RAL to measure the muon lifetime with multi-decay per one time window method. The advantage of our setup, no time window limitation, enables us to test the exponential decay law (EDL) in the long decay time region at the same time. The preliminary analysis set a new upperlimit for the EDL deviation in the muon decay. We accumulated ∼10¹⁰ muon decays and analysis is in progress. This revised version was published online in August 2006 with corrections to the Cover Date.