Quantum diffusion of positive muon in pure tantalum

Quantum diffusion of positive muons has been studied in high purity Ta by zero and longitudinal field muon spin relaxation techniques. We found that the muon hopping rate in Ta is more or less the same as in pure Cu (i.e., \nu\simeq10⁵\sim10⁶\ s^™1), showing a characteristic temperature dependence proportional to T^™\alpha with \alpha ranging from 2 to 0.2 below 20 K. In addition, a step‐like change of the nuclear dipolar width was observed at 60 K associated with the sharp peak of hopping rate, suggesting a change of stable muon sites. This revised version was published online in August 2006 with corrections to the Cover Date.     

Generation of ultra-slow muons for large-scale future applications

The ideas of providing intense high-quality eV to keV muons (μ⁺μ⁻) proposed in the eighties have been tested during the last five years. Recently, remarkable success was marked for ultra-slow μ⁺, while a promising test result was obtained for ultra-slow μ⁻. The ultimate future of these beams is considered. A possible large-scale application to an eventual μ⁺μ⁻ collider is discussed.     

Magnetic properties of crystalline and amorphous DyAg from μSR measurements

Muon spin relaxation in crystalline and amorphous DyAg has been studied in the paramagnetic and magnetically ordered regimes. In cr-DyAg the critical slowing down of the Dy³⁺ spin fluctuation is seen on approaching T_N = 60 K. In the ordered state we observe a Lorentzian field distribution. The muon spin relaxation in am-DyAg approaches at lower temperatures a root exponential law usually encountered in spin glasses.     

Fe site populations in Sm2(Co, Fe)17 and Sm(Co, Fe, Cu, Zr)8.35 alloys

We have investigated the crystallographic site distribution of Fe atoms in Sm₂(Co_1−xFe_x)₁₇ and Sm(Co_0.90−vFe_vCu_0.08---Zr_0.02)_8.35 alloys by means of Mössbauer spectroscopy. Fe shows a strong preference for 2c (dumbbell) sites in the former system, but in the multicomponent alloys such preference is reduced. This result gives support to a model proposed by Ray, according to which Zr-vacancy pairs displace Fe---Fe dumbbell pairs during the solutionizing heat treatment of these permanent-magnet materials.     

Theμ + state under decoupling field observed by spin resonance method in CS2, water and benzene

The muon spin resonance method was applied to measure the ⁺ polarization corresponding to the muon state in diamagnetic compounds in CS₂, water and benzene under 3 kG decoupling field. We observed almost the same diamagnetic polarizations under decoupling field, compared to those at zero decoupling field observed under the transverse field, except in CS₂ The results indicate that most of the so called missing fraction is not associated with diamagnetic species produced as a final state of rapid chemical reactions of muonium in these samples.The authors acknowledge helpful discussions with Professor T. Yamazaki. This work is supported by the Grant-in-Aid of the Japanese Ministry of Education, Culture and Science.     

Fabrication of microbial chip using collagen gel microstructure

A microbial chip was fabricated by filling the micropores on a glass substrate with collagen-embedded Escherichia coli(E. coli) cells, and characterized by scanning electrochemical microscopy (SECM) in a solution containing ferricyanide. The activity of the E. coli cells in the collagen gel microstructure was imaged and characterized with SECM by mapping the localized concentration of ferrocyanide produced by the respiration of the cells. The SECM-based activity measurement detected as low as approximately 100 E. coli cells. Furthermore, the optical-microscopic observation indicated that the E. coli cells on the chip proliferated during the incubation. The sequential SECM measurements were performed for the same E. coli chip to obtain the microbial growth curve for a small number of microorganisms.     

Spin dynamics of the diluted antiferromagnet FexMg1-xTiO3 by muon spin relaxation method

The diluted antiferromanget Fe_xMg_1-xTiO₃ which transforms from the antiferro-magnetic (AF) system to the cluster-glass (CG) one with dilution is investigated by muon spin relaxation measurements. We compare the concentration dependence of the spin dynamics of Fe_xMg_1-xTiO₃ with that of Fe_xMn_1-xTiO₃ and Mn_xMg_1-xTiO₃ which transform from the AF system to the spin-glass one depending on x. It is found that the shape and the temperature variation of the time spectrum in Fe_xMg_1-xTiO₃ for AF to CG depends on the Fe concentration most strongly. This revised version was published online in August 2006 with corrections to the Cover Date.     

Tritium gas handling system for muon catalyzed fusion research at RIKEN-RAL muon facility

For muon catalyzed fusion (μCF) experiments at RIKEN-RAL muon facility, a tritium gas handling system for a high purity D–T target, free from ³ component, has been constructed to perform precise measurements of α-sticking probability in the μCF cycle. The system has been constructed to enable us to purify the target D–T gas by removing ³He component, to adjust the D/T mixing ratio, and to measure the hydrogen isotope components at the experiment site. The whole performance has been confirmed and a tritium gas with the inventory of 56 TBq (1500 Ci) has been operated in the system. This revised version was published online in August 2006 with corrections to the Cover Date.     

μSR study of a mixed compound NiC2O4 2⋅(2-methylimidazole)x(H2O)1-x

We examined the muon spin relaxation (μSR) of mixed compounds NiC₂O₄ 2⋅(2-methylimidazole)_x(H₂O)_1-x with x=1.0 and 0.49. Although the macroscopic magnetic properties are obviously different from each other, both systems exhibit similar behavior in the muon spin relaxation. In addition, in the x=0.49 (SG) sample, a critical slowing down of spin dynamics was not observed in this μSR measurement, though the spin-glass like freezing was observed in the susceptibility measurements. Qualitative explanation of these anomalous observations is given. This revised version was published online in August 2006 with corrections to the Cover Date.