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.     

μSR in polyacetylenes

In a series of μ⁺ experiments either at UT-MSL BOOM or at TRIUMF, we have found that the positive muon can create an interesting and systematic “after-effect” in the well-known organic semiconductor polymer polyacetylene, (CH)_x or (CD)_x: the localized unpaired electron at nearby carbon sites is produced in cis-polyacetylene, to form a muon radical; in trans-polyacetylene, the electron becomes mobile and takes “soliton”-like one dimensional rapid motion along the chain. Recently experiments were extended towards the following three directions: a) diffusion properties of the muon produced solition in trans-polyacetylene; b) the details of radical structure in cis-polyacetylene, and c) μSR experiments on I-doped polyacetylene. These works are reviewed along with the possible future perspectives.     

μSR studies on polyacetylenes

Positive muons were injected into both cis- and trans-polyacetylenes. From the various μSR measurements, the μ⁺ was found to form a radical state with an unpaired electron localized near μ⁺ in cis-polyacetylene, while in trans-polyacetylene it was found to be in a diamagnetic state. Combined with the observed H^?1/2 dependence of the μ⁺ relaxation rate on the applied longitudinal field H in trans-polyacetylene, it was explained by the formation of soliton in trans-polyacetylene. Also the radical state was found to become unstable in iodine-doped polyacetylenes. An explanation is given with respect to the soliton model.