Search

The non-destructive investigation of the chemical state of elements within a material is urgently needed in various scientific research fields. In recent years, non-destructive elemental analysis methods using muons have been developed. These methods identify elements by measuring muonic X-rays emitted from muonic atoms formed by the muon irradiation of the material. Interestingly, muonic atom formation processes are slightly influenced by the chemical state of the muon-capturing atom, and as a result, the muon capture probability of each element and the muonic X-ray emission intensity change depending on the chemical state. By utilizing this effect, it may be possible to know the chemical state at the same time as elemental analysis. In this study, the compositions of γ-Fe2O3and Fe3O4in an ironsand sample were determined using two approaches: muonic X-ray intensity ratios and muon capture ratios. The mixing ratios obtained from the two approaches were consistent with each other and consistent with results of the Mössbauer technique, a completely different analysis method. In this study, non-destructive chemical state analysis using muons was successfully demonstrated, and this method is promising for applications in various research fields.The compositions of γ-Fe2O3and Fe3O4in an ironsand sample were non-destructively determined by muonic X-rays emitted after irradiating the material with a muon beam. The measured compositions are consistent with results obtained using the Mössbauer technique. This chemical analysis method can be applied not only for iron but all elements and is promising for application in various research fields.

To investigate the chemical effect on the muon capture process through a muon transfer reaction from a muonic hydrogen atom, the formation rate of muonic carbon atoms is measured for benzene and cyclohexane molecules in liquid samples. The muon transfer rate to carbon atoms of the benzene molecule is higher than that to the carbon atoms of the cyclohexane molecule. Such a deviation has never been observed among those molecules for gas samples. This may be because the transfers occur from the excited states of muonic hydrogen atoms in the liquid system, whereas in the gas system, all the transfers occur from the 1s(ground) state of muon hydrogen atoms. The muonic hydrogen atoms in the excited states have a larger radius than those in the 1sstate and are therefore considered to be affected by the steric hindrance of the molecular structure. This indicates that the excited states of muonic hydrogen atoms contribute significantly to the chemical effects on the muon transfer reaction.

Focusing effect of muon beam with a tapered capillary method has been investigated in a range from 4.2 to 9.2 MeV (i.e., from 30 to 45 MeV/$c$ in momentum). We injected the muon beam into a pair of narrowing (tapered) plates and tubes made of glass, copper and gold-coated copper, and measured the energy distribution and the profile of the muon outgoing from the outlet. The plates were tilted from an inlet of 40 mm to an outlet of 20 mm. The density enhancement was more prominent with the plates made of heavier elements. The largest beam density enhancement at 10 mm downstream of the outlet was 1.3 with the gold-coated copper narrowing plates. The enhancement was composed of muons scattered with a small angle. Their energy was slightly lost less than that of the initial beam. This effect did not depend on the surface roughness. The density enhancement with the copper narrowing tube was 1.7, where the inlet and outlet sizes were 40 mm square and 10 mm square, respectively. The spin polarization was conserved between incoming and outgoing muons. The result strongly suggests a simple and effective way to increase the muon beam density for a small target.