M. K. Kubo

Nondestructive Elemental Depth-Profiling Analysis by Muonic X-ray Measurement

Elemental analysis of materials is fundamentally important to science and technology. Many elemental analysis methods have been developed, but three-dimensional nondestructive elemental analysis of bulk materials has remained elusive. Recently, our project team, dreamX (damageless and regioselective elemental analysis with muonic X-rays), developed a nondestructive depth-profiling elemental analysis method after a decade of research. This new method utilizes a new type of probe; a negative muon particle and high-energy muonic X-rays emitted after the muon stops in a material. We performed elemental depth profiling on an old Japanese gold coin (Tempo-Koban) using a low-momentum negative muon beam and successfully determined that the Au concentration in the coin gradually decreased with depth over a micrometer length scale. We believe that this method will be a promising tool for the elemental analysis of valuable samples, such as archeological artifacts.

J-PARC decay muon channel construction status

The new Muon Science Facility (MUSE) that is now under construction at J-PARC in the Materials and Life Science Facility (MLF) building will comprise four types of muon channels. In the first stage, a conventional superconducting decay muon channel (D-Line) was constructed, which can extract surface (positive) muons with an expected muon yield of 107/s and decay positive/negative muons up to 120 MeV/c, with an expected muon yield of a few 106/s at 60 MeV/c for both positive and negative muons. This channel will be used for various kinds of muon experiments like ?SR, muon catalyzed fusion and nondestructive elements analysis.

Neutron In‐beam Mössbauer Spectroscopy with a Parallel Plate Avalanche Counter

An in‐beam 57Fe Mossbauer spectroscopy system using a parallel plate avalanche counter has been developed for characterizing chemical species produced after neutron capture reactions. The high signal‐to‐background ratio of the detector enabled us to obtain the first spectrum of semiconductor iron disulfide. A new chemical species of iron, different from the parent compound, arising from the nuclear reaction was clearly observed.

Distribution of boron in wood treated with aqueous and methanolic boric acid solutions

The distributions of boron in Japanese cedar (Cryptomeria japonica D. Don) sapwood blocks treated with aqueous or methanolic boric acid [B(OH)3] solutions were explored through Raman spectroscopy and prompt gamma-ray analysis (PGA). B(OH)3 was the sole boron species observed in Raman spectra of the wood blocks treated with either solution. Plots of weight gain of the treated wood blocks versus boron concentration in treatment solutions were found to be linear. The results indicated that the methanolic solution makes it possible to impregnate wood with much larger amounts of boron than the aqueous solution. PGA confirmed that B(OH)3 was highly enriched near the end grains of the treated wood blocks. Raman measurements suggested that boron content in the bulk of the wood block is not as large as expected from the weight gain of the treated wood blocks when an ordinary air-drying method is used. It was concluded that the aqueous solution impregnates the cell walls of wood with boron more easily than the methanolic solution.

Analysis of boron in wood treated with boric acid solutions using Doppler broadening method of prompt gamma-rays

Wood preservatives such as boric acid and/or borate have been expected to emerge as effective substitutes for chromated copper arsenate (CCA) because of their lower toxicity. However, such preservatives have not been commercially available in Japan because these boron compounds are easily eluted from wood by rainwater. We have applied a multipronged approach to the problem of preventing the easy elution of boron. To obtain knowledge of the chemical species and distribution of boron in wood, we have explored wood treated with aqueous and methanolic boric acid solutions by using Raman spectroscopy. The methods of analyzing boron in the solid state are restricted to Raman spectroscopy and only a few other techniques. Regarding the analysis of boron contained in wood, there has so far been only an electron probe microanalysis (EPMA) study of boron distribution other than our Raman studies. The Raman technique enables us to identify boron species in wood, because boric acid and most borates show several characteristic Raman bands. However, Raman spectroscopy is not sensitive enough to detect low concentrations of boron species in wood and is not suitable for quantitative analysis of solid samples. In general, there are few analytical techniques that can determine the boron content in solids. However, the recent development of neutron-induced prompt gamma-ray analysis (PGA) has allowed us to obtain a powerful tool for the detection of trace amounts of boron in various samples, which is basically in a category of neutron-activation analysis although on-line measurement is absolutely necessary. Boron is one of the elements for which PGA has an ultimate sensitivity by using 478-keV prompt gamma-rays emitted from Li produced in the B (n, a) Li reaction. Li represents the Li atomic nucleus in an excited state. The cross section of the nuclear reaction is 3838 barn for the thermalneutron capture. Such a large cross section should lead to high analytical sensitivity. The PGA analysis of boron provides us not only the information on boron contents but also on boron states by probing the Doppler broadened line shape of 478-keV gamma-ray. The initial recoil energy imparted to a Li ion by the nuclear reaction is 840keV, corresponding to an initial velocity (4.8 × 10 ms) of a Li nucleus. A Li nucleus with a lifetime of 1.05 × 10 s emits a 478-keV gamma-ray in flight, which leads to Doppler energy shift. Because the direction of the Li recoil is isotropic, the spectral line shape is observed with Doppler broadening. An energetic Li ion loses kinetic energy through interaction with atoms that the moving ion encounters in medium. It was proved experimentally and theoretically that the velocity v(t) decreases with time t as follows:

Muonic X-ray measurements on mixtures of CaO/MgO and Fe 3 O 4 /MnO

Abstract Elemental analysis by measurement of muonic X-rays shows great potential for analyzing the elemental composition of a bulk material at a specific depth without sample destruction. For quantitative analysis, muon capture probability is the most important parameter. In this work, the muon capture ratios and muonic X-ray intensity patterns of metal oxides for geochemically and cosmochemically important compounds, MgO, CaO, MnO and Fe3O4, were determined. The muon capture ratios of Ca/Mg and Fe/Mn were proportional to the mixing ratios of CaO/MgO and Fe3O4/MnO. From this relationship, the elemental composition can be determined from the muonic X-ray intensity ratio alone.

Elemental Analysis of Bronze Artifacts by Muonic X-ray Spectroscopy

Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan Colleage of Liberal Arts, International Christian University, 3-10-2 Osawa, Mitaka, Tokyo 181-8585, Japan Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan Department of Communication Engineering and Informatics, The University of Electro-Communications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan 4 Nishina Center for Accelerator-Based Science, RIKEN, Hirosawa, Wako, Saitama, 351-0198, Japan Advanced Science Research Center, Japan Atomic Energy Agency, 2-4 Shirakata-Shirane, Tokai, Ibaraki 319-1195, Japan 6 College of Engineering, Shibaura Institute of Technology, Saitama-shi, Saitama 337-8570, Japan 7 National Museum of Japanese History, Sakura, Chiba, 285-8502, Japan