# 15th International Conference on Muon Spin Rotation, Relaxation and Resonance

28 August 2022 to 2 September 2022
Science and Technology Campus, University of Parma
Europe/Rome timezone
Submission deadline for Conference Proceedings extended until 3 October

## Negative muon spin relaxation in water and ice

28 Aug 2022, 12:00
15m
Aula dei Cavalieri, University Central Palace, via Università 12

#### Aula dei Cavalieri, University Central Palace, via Università 12

Oral Molecular chemistry and chemical physics

### Speaker

Yoko Kimura (Dept. Phys. Osaka Univ.)

### Description

Muons are the main component of cosmic ray particles on the earth, and most of the cosmic ray muons are injected into water or ice, which occupy more than 70% of the earth's surface. When negative muons ($\mu$$^-) stop in H_2O, they are mainly trapped by oxygen nuclei and form muonic oxygen atoms O\mu$$^-$, and about 15% of O$\mu$$^- atoms finally change to stable nitrogen isotopes ^{14}N or ^{15}N via the neutron emission after the muon capture process. The nitrogen isotopes produced by such a process may be chemically active due to their high recoil energy and may form various nitrogen compounds through reactions with water molecules. In this situation, \mu^-SR spectroscopy is suitable for studying the behavior of such active nitrogen in H_2O, since O\mu^- atoms also act chemically as nitrogen. In the present study, we measured \mu^-SR spectra in water and ice to approach what kind of nitrogen compounds are formed by cosmic-ray negative muons, and how they affect the surrounding chemical environment. Experiments were carried out at the D1 beamline in the Materials and Life Science Experimental Facility (MLF) of J-PARC. H_2O and D_2O samples were irradiated with a negative muon beam (47 MeV/c, double pulse), and ZF and LF-\mu$$^-$SR spectra were measured. The result shows that the relaxation due to the nuclear dipolar field is observed in solid H$_2$O and D$_2$O at 200 K. The field distribution widths were deduced to be $\Delta_H$=0.27 $\mu$$s^{-1} and \Delta_D=0.066 \mu$$s^{-1}$, for H$_2$O and D$_2$O respectively. The relationship between these two values is well explained by the difference in the spins and magnetic moments of proton and deuteron.
In this conference, we will discuss possible chemical states based on the present results.

### Primary author

Yoko Kimura (Dept. Phys. Osaka Univ.)

### Co-authors

Dr Mototsugu Mihara (Dept. Phys. Osaka Univ.) Prof. Kenya Kubo (ICU) Dr Pant Amba Datt (KEK) Ms Yurika Otani (Dept. Phys. Osaka Univ.) Mr Gen Takayama (Dept. Phys. Osaka Univ.) Mr Takato Sugisaki (Dept. Phys. Osaka Univ.) Prof. Koichiro Shimomura (KEK) Prof. Akihiro Koda (KEK) Dr Soshi Takeshita (KEK)

### Presentation Materials

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