Yasuhiro Miyake

Inhibition and anti-inhibition effects of positronium formation in cyclohexane and their relation to radiation chemistry

Abstract Positronium formation in cyclohexane has been studied using C 2 H 5 Br or CCl 4 as an inhibitor and C 6 F 6 as an anti-inhibitor. The results are analyzed using an empirical formula which is well established in radiation chemistry for electron scavenging reactions in cyclohexane. The reactivity parameters derived from the radiation chemistry are shown to successfully reproduce the experimental results. Very close correlation between positronium formation and radiation chemistry is evident, and the spur reaction model of positronium formation is corroborated. From a simple model of the positron spur in which only a single ion pair and a positron is assumed, it is estimated that about 75% of the spur electron combines with the positron.

Muonium radicals in benzene-styrene mixtures

Muonium radicals were observed through theirμSR precession frequencies in high transverse magnetic fields in pure benzene, pure styrene and their mixtures, all as liquids at room temperature. In benzene-styrene mixtures, the radicals obtained in each pure liquid are both present, so no slow (10−9−10−5 s) intermolecular exchange occurs; but strong selectivity was found with the formation of the radical from styrene being about eight-times more probable than the radical from benzene.

Muonium atoms observed in neopentane and tetramethylsilane

Abstract Muonium has been observed in neopentane and tetramethylsilane by a pulsed MuSR method. The probability of muonium formation was ≈ 20%, and its relaxation times were 8 and 2.6 μs for liquid neopentane and tetramethylsilane, respectively. The rate of muonium relxation has been shown to be correlated well with the dissociation energy of the CH bonding.

Inhibition and anti-inhibition effects of positronium formation in cyclohexane re-examined

Abstract Previous results of inhibition and anti-inhibition of positronium (Ps) formation in cyclo hexane are re-examined using energy measurement of the Doppler broadened annihilation radiation and angular correlation technique. Evidence for the formation of some e+ containing compound is obtained for CCl4 solutions, but similar compound formation has not been confirmed for C2H5Br solutions. The e+ containing compound is mainly attributable to positronium chloride which is formed as a result of the reaction between e+ and the product of the electron scavenging reaction. Discussion is made about its role in the inhibition of Ps formation. Anomalously large inhibition factor α of CCl4 is re-examined and possible explanations are given in terms of e+CCl4 formation or stable molecular anion, CCl4-, formation.

Muonium formation on powdered platinum surfaces

Abstract Muonium formation was verified in platinum powders under vacuum by muonium spin rotation (MuSR) spectroscopy. Muonium yields of 13(1)% and 9(3)% per incident muon were obtained for Pt powders with mean particle diameters of 30 and 200 nm, respectively. The disappearance of the muonium signal under oxygenic or atmospheric environment indicates that muonium stays outside the Pt particles. It can be postulated that reactive collision between muonium and atomic oxygen is a predominant process on the platinum surface treated by hydrogen.

Evidence for muonium emission from an SiO2 layer on n-type Si and the positive muon state in Si

Evidence for the emission of slow muonium atoms from a 3.0-nm-thick SiO2 layer covered on an n-type Si is reported. Also, upon applying an rf-resonance technique at the muon frequency, a time-differential observation of a delayed state-change from muonium to diamagnetic muon at room temperature was observed. Combining results obtained by use of longitudinal field decoupling and transverse spin rotation methods, the conversion rate was estimated to be 5 to 10 μs−1. Both of the above results, namely the observation of the emission and state-change of muonium, suggest a process in which μ+ initially captures an electron from Si, then quickly converts to μ+ again during thermal diffusion in the Si towards the SiO2 layer. Within the oxide layer, muonium is again formed and subsequently is emitted from the SiO2 surface.

Ultra-slow muon facility for surface HFI studies

A concept, a design, a construction and an account of commissioning experiments are given for the recently completed ultra-slow muon facility at the pulsed muon facility of UT-MSL/KEK. The intense (more than 103/s) slow μ+ beam with an extremely narrow phase-space volume (0.2 eV×(3 cm)2) to be produced in this facility will open a new muon science including surface physics and chemistry and fundamental atomic physics.

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

The muon spin resonance method was applied to measure theμ+ 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.

Electron scavenger effects on diamagnetic muon polarization in cyclohexane

The effect of electron scavengers on diamagnetic polarization PD in cyclohexane were examined and compared with the experimental yield of Ps formation (inhibition and anti-inhibition effects) for the same solutions. The effect of C6F6 on PD has been shown to sharply contrast, as we call “non anti-inhibition”, to the anti-inhibition effect in Ps formation. These results suggest that Muonium formation is different from Ps formation, and does not agree with the simple spur reaction model.

The Development of a Non-Destructive Analysis System with Negative Muon Beam for Industrial Devices at J-PARC MUSE

Motonobu Tampo1, Kouji Hamada1, Naritoshi Kawamura1, Makoto Inagaki2, Takashi U. Ito3, Kenji M. Kojima1, Kenya M. Kubo4, Kazuhiko Ninomiya2, Patrick Strasser1, Go Yoshida2 and Yasuhiro Miyake1 1Institute of Materials Structure Science, KEK, Tokai, Ibaraki 319-1195, Japan 2Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama Toyonaka, Osaka, 560-0043 Japan 3Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki, 319-1195, Japan 4International Christian University, Mitaka, Tokyo, 181-8585, Japan