実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）MLF Experimental Report

提出日 Date of Report: June 17, 2011
装置責任者 Name of responsible person

課題番号 Project No. 2010A0056

Khashayar Ghandi
実験課題名 Title of experiment: Mu kinetics in methanol

装置名 Name of Instrument/（BL No.）
MUSE

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Khashayar Ghandi

Nov 21/ 2010 Nov 23 /2010

所属 Affiliation

Professor at Mount Allison University
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.

All samples were CH3OH (methanol), or solutions of acetone in methanol

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

Our research goals were: 1) to start muonium chemistry in J-PARC by detecting
long-lived muonium signals, 2) to test the feasibility of the kinetics experiments withthe target cells under a wide temperature range using a cryostat, 3) to measure thekinetics of reaction of Muonium and acetone in methanol.
Muonium (Mu=μ+e−), with a mass only ~ 1/9’th that of its protonic cousin, is quite
simply the light isotope of the H-atom. Hydrogen is the simplest atom in nature andconsequently the study of its interactions and chemical reaction rates has been central
to the field of reaction dynamics. Indeed H atom and Mu are quarks of chemists since
studying their reactions provide chemists with the most fundamental aspects ofchemistry and chemical dynamics. Therefore, to initiate muonium chemistry in
J-PARC after our initial work on muonium formation in methanol at J-PARC (it isjust submitted) we decided to investigate the possibility of studying Mu kinetics in
non-aqueous systems over a wide range of temperatures, in particular in methanol. In
our work on Mu formation in methanol, we have observed Mu over a wide range oftemperature from room temperature up to melting point of methanol.
12. 実験方法及び結果（つづき） Experimental method and results (continued)

In the work of 2010A0056 for the first time we measured Mu kinetics in methanol
over a wide range of temperature.
A typical histogram is presented in Figure 1.
0.51

Asymmetry

0.50
0.49
0.48
0.47
0.46
0.0

0.5

1.0

1.5

2.0

time /ms
Figure 1 Mu signal in methanol at 180 K (no acetone is added to this sample). The relaxation rates from suchdata in pure methanol were used as background relaxation rates.

The asymmetry parameter, A(t), in a transverse field experiment includes
contributions from paramagnetic Mu, as well as free radical and diamagnetic
molecules:A(t ) = Σi Ai exp(−λ i t ) cos( wi t + φi )(1)

where t is time, Ai is the asymmetry of the fraction i in its given environment, λi is therelaxation rate of the muon spin in that environment, ωi is the corresponding
precession frequency, and ϕi is the initial phase of this fraction. The parameters ofinterest in this work — λi —were extracted from fits of eqn (1) to experimental data,and provide the kinetics information. In low fields, the two muonium ‘‘triplet’’frequencies are very close and unresolved, so we fit the asymmetry with a single
oscillating term for Mu and a single oscillating term for the diamagnetic species.
In the homogeneous kinetics regime of interest in this work the time dependence ofthe muon polarization in the Mu atom can be represented by the simple first-orderdecay expression:[Mu]t = [Mu]0 e −λMu t (2)where λMu= kMu[X] is a pseudo first-order rate constant and kMu is the total rate constantfor the reaction Mu + X with reactant “X”. In our case X is acetone.
22. 実験方法及び結果（つづき） Experimental method and results (continued)

It should be noted that the total thermalization time of the muon is less than 1 ns,
much smaller than typical reaction times, which are set by reactant concentrations
to be on the order of 1 μs; therefore the Mu decay rate λMu is a measure of thermal
reaction rates. In addition to chemical reaction the measured decay rate includes
a component λb due to “background” relaxation, e.g. spin dephasing due tomagnetic field inhomogeneity. The total relaxation rate is expressed asλ Mu = λ Ch + λ b(3)where λCh = kMu[X] is due to chemical reaction of Mu with species X (acetone in ourcase).
The rate constants measured in this way, are presented in Figure 2 as an Arrhenius
plot.
Arrhenius Plot - Acetone in Methanol Reacting With Mu
23.5

ln (k/M-1s-1)

22.5

21.5

20.5

19.5

18.5
3

45

1000/T/K

Figure 2 Arrhenius plot of the rate constants for reaction of Mu with acetone in methanol.

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