Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed seventeen Ryugu samples measuring 1-8 mm. CO₂-bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu’s parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and Ca, Al-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed by aqueous alteration reactions at low temperature, high pH, and water/rock ratios < 1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate Ryugu’s parent body formed ~ 2 million years after the beginning of Solar System formation.

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-Fe2O3 and Fe3O4 in 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.

Radium is refocused from the viewpoint of an environmental pollutant and cancer therapy using alpha particles, where it mainly exists as a hydrated ion. We investigated the radium hydration structure and the dynamics of water molecules by extended X-ray absorption fine structure (EXAFS) spectroscopy and ab initio molecular dynamics (AIMD) simulation. The EXAFS experiment showed that the coordination number and average distance between radium ion and the oxygen atoms in the first hydration shell are 9.2 ± 1.9 and 2.87 ± 0.06 Å , respectively. They are consistent with those obtained from the AIMD simulations, 8.4 and 2.88 Å . The AIMD simulations also revealed that the water molecules in the first hydration shell of radium are less structured and more mobile than those of barium, which is an analogous element of radium. Our results indicate that radium can be more labile than barium in terms of interactions with water.

The present study reports that the ground- and excited-state Re₆(23e)/ReRe₆(24e) redox potentials of an octahedral hexanuclear rhenium(III) complex can be controlled by systematically changing in the number and type of the N-heteroaromatic ligand (L) and the number of chloride ions at the six terminal positions. Photoirradiation of [Re₆(μ₃-S)₈Cl₆]^4– with an excess amount of L afforded a mono-L-substituted hexanuclear rhenium(III) complex, [Re₆(μ₃-S)₈Cl₅(L)]^3– (L = 4-dimethylaminopyridine (dmap), 3,5-lutidine (lut), 4-methylpyridine (mpy), pyridine (py), 4,4ʹ-bipyridine (bpy), 4-cyanopyridine (cpy), and pyrazine (pz)). The bis- and tris-lut-substituted complexes, trans- and cis-[Re₆(μ₃-S)₈Cl₄(lut)₂]^2– and mer-[Re₆(μ₃-S)₈Cl₃(lut)₃]^–, were synthesized by the reaction of [Re₆(μ₃-S)₈Cl₆]^3– with an excess amount of lut in refluxed N,N-dimethylformamide. The mono-L-substituted complexes showed one-electron redox processes assignable to E_1/2[Re₆(23e)/Re₆(24e)] = 0.49–0.59 V vs. Ag/AgCl. The ground-state oxidation potentials were linearly correlated with the pKa of the N-heteroaromatic ligand [pKa(L)], the ¹H NMR chemical shift of the ortho proton on the coordinating ligand, and the Hammett constant (σ) of the pyridyl-ligand substituent. The series of [Re₆(μ₃-S)₈X_6–n(L)_n]^n–4 complexes (n = 0, X = Cl, Br, I, or NCS; n = 1–3, X = Cl) showed a linear correlation with the sum of the Lever electrochemical parameters at the six terminal ligands (ΣE_L). The cyclic voltammograms of the mono-L-substituted complexes (L = bpy, cpy, and pz) showed one-electron redox waves assignable to E_1/2(L⁰/L^–) = –1.28 to –1.48 V vs. Ag/AgCl. Two types of photoluminescences were observed for the complexes, originating from the cluster core-centered excited triplet state (³CC) for L = dmap, lut, mpy, and py, and from the metal-to-ligand charge-transfer excited triplet state (³MLCT) for L = bpy, cpy, and pz. The complexes with the ³CC character exhibited emission features and photophysical properties similar to those of ordinal hexanuclear rhenium complexes. The emission maximum wavelength of the complexes with ³MLCT shifted to the longer-wavelength in the order L = 4-phenylpyridine (ppy), bpy, cpy, and pz, which agreed with the difference between E_1/2[Re₆(23e)/Re₆(24e)] and E_1/2(L⁰/L^–). The calculated oxidation potential of the excited hexanuclear rhenium complex with the ³CC character was linearly correlated with pKa(L), σ, and ΣE_L. The ground- and excited-state oxidation potentials were finely tuned by the combination of halide and L ligands at the terminal positions.

After the Fukushima nuclear accident, atmospheric ¹³⁴Cs and ¹³⁷Cs measurements were taken in Fukushima city for 8 years, from March 2011 to March 2019. The airborne surface concentrations and deposition of radiocesium (radio-Cs) were high in winter and low in summer; these trends are the opposite of those observed in a contaminated forest area. The effective half-lives of ¹³⁷Cs in the concentrations and deposition before 2015 (0.754 and 1.30 years, respectively) were significantly shorter than those after 2015 (2.07 and 4.69 years, respectively), which was likely because the dissolved radio-Cs was discharged from the local terrestrial ecosystems more rapidly than the particulate radio-Cs. In fact, the dissolved fractions of precipitation were larger than the particulate fractions before 2015, but the particulate fractions were larger after 2016. X-ray fluorescence analysis suggested that biotite may have played a key role in the environmental behavior of particulate forms of radio-Cs after 2014. However, the causal relationship between the seasonal variations in particle size distributions and the possible sources of particles is not yet fully understood. The current study also proposes an evaluation method of the consistency of a numerical model for radio-Cs resuspension and suggests that improvements to the model are necessary.

Elemental analysis based on muonic X-rays resulting from muon irradiation provides information about bulk material composition without causing damage, which is essential in the case of precious or otherwise unreachable samples, such as in archeology and planetary science. We developed a three-dimensional (3D) elemental analysis technique by combining the elemental analysis method based on negative muons with an imaging cadmium telluride double-sided strip detector (CdTe-DSD) designed for the hard X-ray and soft \gamma-ray observation. A muon irradiation experiment using spherical plastic samples was conducted at the Japan Proton Accelerator Research Complex (J-PARC); a set of projection images was taken by the CdTe-DSD, equipped with a pinhole collimator, for different sample rotation angles. The projection images measured by the CdTe-DSD were utilized to obtain a 3D volumetric phantom by using the maximum likelihood expectation maximization algorithm. The reconstructed phantom successfully revealed the 3D distribution of carbon in the bulk samples and the stopping depth of the muons. This result demonstrated the feasibility of the proposed non-destructive 3D elemental analysis method for bulk material analysis based on muonic X-rays.

Structures of La(III) and Ba(II) complexes and their stabilities were investigated to develop a stable chelating ligand for Ac(III) and Ra(II) which are of interest in nuclear medicine using alpha particles. The La(III) and Ba(II) complexes (1 and 2) with a diaza-18-crown-6 ether bearing pyridine phosphonic acid ethyl ester pendant arms (L1) and the complexes (3 and 4) with a diaza-18-crown-6 ether bearing pyridine phosphonate pendant arms ((H₂L2)²⁻) were synthesized and characterized. The structures of the new complexes were determined by single-crystal X-ray analysis. The La(III) complexes, 1 and 3, exhibited 11-coordinate structures, whereas the Ba(II) complexes, 2 and 4 exhibited 11- and 10-coordinate geometries, respectively. Potentiometric titrations were performed to determine the acid–base equilibrium and the complex formation reactions of the La(III) and Ba(II) complexes. In addition, the speciation of the complexes and the pH dependencies of the fractions in the aqueous solutions were performed. For the La(III) complexes, the species with the ligand bearing pyridine phosphonate pendant arms were observed to be more stable than those with the ligand bearing pyridine phosphonate ester pendant arms. The Ba(II) complexes showed the opposite trend. The species with the pyridine phosphonate ester ligand were observed to be more stable than the species with the pyridine phosphonate type ligand.