Creation of Mo/Tc@C60 and Au@C60 and molecular-dynamics simulations

The formation of middle- and/or high-weight atom (Mo, Au)-incorporated fullerenes was investigated using radionuclides produced by nuclear reactions. From the trace radioactivities of ⁹⁹Mo/⁹⁹mTc or ¹⁹⁴Au after high-performance liquid chromatography, it was found that the formation of endohedral and/or heterofullerene fullerenes in ⁹⁹Mo/⁹⁹mTc and ¹⁹⁴Au atoms could occur by a recoil process following the nuclear reactions. Furthermore, the ⁹⁹mTc (and ¹⁹⁴Au) atoms recoiled against β-decay remained present inside these cages. To confirm the produced materials experimentally, ab initio molecular dynamics (MD) simulations based on an all-electron mixed-basis approach were performed. The possibility of the formation of endohedral fullerenes containing Mo/Tc and Au atoms is verified; here, the formation of heterofullerenes is excluded by MD simulations. These findings suggest that radionuclides stably encapsulated by fullerenes could potentially play a valuable role in diagnostic nuclear medicine

Activation detector measurements at the hadron absorber of the NuMI neutrino beamline at Fermilab

Two-dimensional distributions of the production rates of radionuclides in aluminum and gold activation detectors, placed behind the hadron absorber of the NuMI beamline at Fermilab were obtained in an experiment for shielding data as a dump in a proton-beam-energy domain above 100 GeV. The production rates of 7 Be, 22 Na, and 24 Na in the aluminum activation detectors and those of 185 Os, 194 Au, and 196 Au in the gold activation detectors were obtained from the γ-ray spectra of HPGe counters. It was concluded that in these distributions showed some peaks that can be attributed to a lack of shielding caused by the gaps for arraignment and cooling in the hadron absorber. The radionuclides in the activation detectors were mainly produced by neutrons, protons and pions, according to analyses of calculated results by the PHITS code

Oxygen isotope evidence from Ryugu samples for early water delivery to Earth by CI chondrites

The delivery of water to the inner Solar System, including Earth, is still a debated topic. A preferential role for hydrated asteroids in this process is supported by isotopic measurements. Carbonaceous chondrite (CC) meteorites represent our main source of information about these volatile-rich asteroids. However, the destruction of weaker materials during atmospheric entry creates a bias in our CC data. The return of surface materials from the C-type asteroid 162173 Ryugu by the Hayabusa2 spacecraft provides a unique opportunity to study high-porosity, low-density, primitive materials, unrepresented in the meteorite record. We measured the bulk oxygen isotope composition from four Ryugu particles and show that they most closely resemble the rare CI (CC Ivuna-type) chondrites, but with some differences that we attribute to the terrestrial contamination of the CI meteorites. We suggest that CI-related material is widespread among carbonaceous asteroids and a more important source of Earth’s water and other volatiles than its limited presence in our meteoritic collection indicates

A pristine record of outer Solar System materials from asteroid Ryugu’s returned sample

Volatile and organic-rich C-type asteroids may have been one of the main sources of Earth’s water. Our best insight into their chemistry is currently provided by carbonaceous chondritic meteorites, but the meteorite record is biased: only the strongest types survive atmospheric entry and are then modified by interaction with the terrestrial environment. Here we present the results of a detailed bulk and microanalytical study of pristine Ryugu particles, brought to Earth by the Hayabusa2 spacecraft. Ryugu particles display a close compositional match with the chemically unfractionated, but aqueously altered, CI (Ivuna-type) chondrites, which are widely used as a proxy for the bulk Solar System composition. The sample shows an intricate spatial relationship between aliphatic-rich organics and phyllosilicates and indicates maximum temperatures of ~30 °C during aqueous alteration. We find that heavy hydrogen and nitrogen abundances are consistent with an outer Solar System origin. Ryugu particles are the most uncontaminated and unfractionated extraterrestrial materials studied so far, and provide the best available match to the bulk Solar System composition

チキュウガイ キゲン ブッシツ ノ カガク ソセイ ト セイセイ キコウ ニ カンスル ケンキュウ

京都大学0048新制・課程博士博士(工学)甲第13832号工博第2936号新制||工||1434(附属図書館)UT51-2008-C748京都大学大学院工学研究科物質エネルギー化学専攻(主査)教授 柴田 誠一, 教授 垣内 隆, 教授 山名 元学位規則第4条第1項該当Doctor of EngineeringKyoto UniversityDA

Application of neutron activation analysis to micro gram scale of solid samples

An instrumental neutron activation analysis (INAA) procedure for analyzing extremely small samples was developed and applied to two kinds of extraterrestrial samples. A few mg of the Allende meteorite as well as the JB-1 basalt can work well as a reference sample for a relative method. To evaluate the applicability of this INAA procedure, detection limits are presented and compared with the elemental contents in a potential sample to be analyzed. The possibility of reuse of neutron-irradiated samples for mass spectrometry was noted by indicating degree of increase in isotopic abundance for noble gas and long-lived radioactive nuclides

Accurate Determination of Chlorine, Bromine, and Iodine in Sedimentary Rock Reference Samples by Radiochemical Neutron Activation Analysis and a Detailed Comparison with Inductively Coupled Plasma Mass Spectrometry Literature Data

Trace amounts of three halogens (chlorine, bromine, and iodine) were determined using radiochemical neutron activation analysis (RNAA) for nine sedimentary rocks and three rhyolite samples. To obtain high-quality analytical data, the radiochemical procedure of RNAA was improved by lowering the background in gamma-ray spectrometry and completing the chemical procedure more rapidly than in conventional procedures. A comparison of the RNAA data of Br and I with corresponding inductively coupled plasma mass spectrometry (ICPMS) literature data revealed that the values obtained by ICPMS coupled with pyrohydrolysis preconcentration were systematically lower than the RNAA data for some reference samples, suggesting that the quantitative collection of Br and I cannot always be achieved by the pyrohydrolysis for some solid samples. The RNAA data of three halogens can classify sedimentary rock reference samples into two groups (the samples from inland water and those from seawater), implying the geochemical significance of halogen data