Measurement of the average polarization of12B in the polarized-muon capture reaction12C(μ −,v μ)12B (g.s.)

The average polarization P_av of the recoil nucleus¹²B (ground state) produced by the polarized-muon capture reaction¹²C(^–,v )¹²B was measured by a new approach which involved the muon spin resonance, and the adoption of Grafoil as a carbon target where the polarization of¹² B can be preserved completely under 3 kG holding field. Our observed resultP _av=0.473±0.053 yields g_p/g_A=9.6 _–2.7 ^2.4 which seems to be consistent with the canonical PCAC prediction within the error.The authors would like to express their sincere thanks to the members of the Meson Science Laboratory and of the Van de Graaff Accerelator at Osaka University. They also acknowledge helpful discussions and suggestions given by Professors M. Morita, H. Ohtsubo and K. Kubodera. This work is supported by the Grant-in-Aid of the Ministry of Education, Science and Culture.     

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.     

Measurement of the average polarization of12B in the polarized-muon capture by12C: Magnitude of the induced pseudoscalar form factor

The average polarization of the nucleus¹²B (bound state) produced in the polarized-muon capture reaction¹²C(μ ^?,v _μ )¹²B was measured by the muon spin resonance method in a pulsed muon beam. The polarization of¹²B was maintained completely under a magnetic field of 3 kG in a Grafoil target. After the observed result was corrected for the contribution from the excited states of¹²B, P_av (ground state) was deduced to be 0.462±0.053. This result yieldsg _P /g _A =10.1 _?2.6 ^+2.4 , which is almost consistent with the PCAC prediction.     

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.     

μSR studies of YFeMnO4

Muon spin relaxation (SR) studies were carried out on YFeMnO₄. Two interesting phenomena were found in measurements of longitudinal relaxation time spectra atT>T _cusp for a single crystal: (1) difference of the relaxation rates between the directions parallel with and perpendicular to thec-axis, and (2) suppression of local field fluctuations in a longitudinal external field. The spectra atT >T _cusp were reproduced with the function exp[-(₀ t)]. The results are discussed under a picture of the magnetic spin fluctuations of triangular antiferromagnets.