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Ninomiya, Kazuhiko*; Osawa, Takahito; Terada, Kentaro*; Wada, Taiga*; Nagasawa, Shunsaku*; Chiu, I.-H.; Nakamura, Tomoki*; 40 of others*
Meteoritics & Planetary Science, 59(8), p.2044 - 2057, 2024/08
Times Cited Count：4 Percentile：48.74(Geochemistry & Geophysics)Samples from asteroid Ryugu, brought back by asteroid explorer Hayabusa2 are important for investigating the origin and evolution of the solar system. Here, we report the elemental compositions of a 123 mg Ryugu sample determined with a nondestructive muon elemental analysis method. This method is a powerful tool for determining bulk chemical composition, including light elements such as C, N, and O. From the muonic X-ray spectra with three carbonaceous chondrites, the relationship between the elemental composition and muonic X-ray intensity was determined for each element. Calibration curves showed linearity, and the elemental composition of Ryugu was quantitatively determined. The results reflect the average bulk elemental composition of asteroid Ryugu owing to the large amount of samples. Ryugu has an elemental composition similar to that of Orgueil (CI1), and should be classified as CI1. However, the O/Si ratio of Ryugu is 25% lower than that of Orgueil, indicating that Orgueil may have been seriously contaminated by terrestrial materials after its fall to Earth. These results indicate that the Ryugu sample is more representative than the CI chondrites as a solid material of the solar system.
Osawa, Takahito; Nagasawa, Shunsaku*; Ninomiya, Kazuhiko*; Takahashi, Tadayuki*; Nakamura, Tomoki*; Wada, Taiga*; Taniguchi, Akihiro*; Umegaki, Izumi*; Kubo, Kenya*; Terada, Kentaro*; et al.
ACS Earth and Space Chemistry (Internet), 7(4), p.699 - 711, 2023/04
Times Cited Count：9 Percentile：64.17(Chemistry, Multidisciplinary)The concentrations of carbon and other major elements in asteroid samples provide very important information on the birth of life on the Earth and the solar-system evolution. Elemental analysis using muonic X-rays is one of the best analytical methods to determine the elemental composition of solid materials, and notably, is the only method to determine the concentration of light elements in bulk samples in a non-destructive manner. We developed a new analysis system using muonic X-rays to measure the concentrations of carbon and other major elements in precious and expectedly tiny samples recovered from the asteroid Ryugu by spacecraft Hayabusa2. Here we report the development process of the system in 4 stages and their system configurations, The analysis system is composed of a stainless-steel analysis chamber, an acrylic glove box for manipulating asteroid samples in a clean environment, and Ge semiconductor detectors arranged to surround the analysis chamber. The performance of the analysis system, including the background level, which is crucial for the measurement, was greatly improved from the first stage to the later ones. Our feasibility study showed that the latest model of our muonic X-ray analysis system is capable of determining the carbon concentration in Hayabusa2's sample model with an uncertainty of less than 10 percent in a 6-day measurement.
