9:00 AM - 9:15 AM
[PPS08-11] Development of Isotope Nanoscope for in-situ noble gas analysis
★Invited Papers
Keywords:SIMS, Noble gas, Mass spectrometry
Noble gases with stable isotopes (He, Ne, Ar, Kr, Xe) have very low abundances in rocks [1]. Noble gases have different isotopic compositions in materials of different origin. Therefore, noble gases are studied as tracer elements in the earth and planetary sciences. Elemental ratios and isotopic ratios are highly variable due to secondary additions such as radioactive decay. Chronological studies are performed using radiogenic and cosmogenic noble gases. We have developed in-situ noble gas isotope analysis and analyzed natural samples using a secondary neutral particle mass spectrometer called LIMAS (Laser Ionization MAss nanoScope) installed at Hokkaido University. Here, the installation of the instrument and the recent results with LIMAS are presented.
Conventional noble gas mass spectrometry has used a sector-type mass spectrometer and a static operation to perform quantitative and high sensitive noble gas isotope analysis [2]. On the other hand, the amount of sample is about ng to g for rock samples because of the extremely low concentration of noble gases in rocks. Therefore, microbeam analysis such as secondary ion mass spectrometry (SIMS) has not been used. In addition, noble gases have a higher ionization potential than other elements, making them unsuitable for SIMS analysis.
LIMAS has nm-scale spatial resolution using a Ga focused ion beam and a femtosecond laser that can ionize all elements by post-ionization [3]. Our research group developed and modified the LIMAS instrument for noble gas analysis from starting in 2011 [4–6]. The 4He analysis is now possible with a lower detection limit of 2 × 1017 atoms cm-2 (at a primary ion beam current of 30 nA) and a spatial resolution of about 200 nm (at a primary ion beam current of 1 nA).
A large amount of CPU resources is required for data processing because LIMAS is equipped with a time-of-flight mass spectrometer. We have developed a program for real-time data reduction and efficient data storage to make effective use of CPU resources [7].
After three years of trial and error, we were able to perform depth profile of the solar wind irradiated sample brought back by the NASA Genesis mission [8]. Then, we obtained scientific results, such as He ion imaging in meteorites [9], solar wind depth profiling of lunar samples [10], and solar wind depth profiling of Itokawa particles [11]. Helium isotope imaging has revealed regolith formation processes. Solar wind depth profiling would have revealed characteristics of the past solar wind. We were able to study the solar wind noble gas isotopes in the extraterrestrial materials using the novel analytical method. In the future, the quantitative analysis allows us to perform simultaneous multi-element isotope analysis and discuss the origin of the solar wind gas-rich samples using isotope ratios.
References: [1] Allègre et al. EPSL, 185, 49 (2001). [2] Sumino, JMSSJ, 63, 14 (2015). [3] Ebata et al. SIA, 44, 635 (2012). [4] Bajo et al. SIA, 48, 1190 (2016). [5] Tonotani et al. SIA, 49, 1122 (2016). [6] Nagata et al. APE, 12, 085005 (2019). [7] Bajo et al. SIA, 51, 35 (2019). [8] Bajo et al. GJ, 49, 559 (2015). [9] Wada et al. this session. [10] Otsuki et al. this session. [11] Obase et al. this session.
Conventional noble gas mass spectrometry has used a sector-type mass spectrometer and a static operation to perform quantitative and high sensitive noble gas isotope analysis [2]. On the other hand, the amount of sample is about ng to g for rock samples because of the extremely low concentration of noble gases in rocks. Therefore, microbeam analysis such as secondary ion mass spectrometry (SIMS) has not been used. In addition, noble gases have a higher ionization potential than other elements, making them unsuitable for SIMS analysis.
LIMAS has nm-scale spatial resolution using a Ga focused ion beam and a femtosecond laser that can ionize all elements by post-ionization [3]. Our research group developed and modified the LIMAS instrument for noble gas analysis from starting in 2011 [4–6]. The 4He analysis is now possible with a lower detection limit of 2 × 1017 atoms cm-2 (at a primary ion beam current of 30 nA) and a spatial resolution of about 200 nm (at a primary ion beam current of 1 nA).
A large amount of CPU resources is required for data processing because LIMAS is equipped with a time-of-flight mass spectrometer. We have developed a program for real-time data reduction and efficient data storage to make effective use of CPU resources [7].
After three years of trial and error, we were able to perform depth profile of the solar wind irradiated sample brought back by the NASA Genesis mission [8]. Then, we obtained scientific results, such as He ion imaging in meteorites [9], solar wind depth profiling of lunar samples [10], and solar wind depth profiling of Itokawa particles [11]. Helium isotope imaging has revealed regolith formation processes. Solar wind depth profiling would have revealed characteristics of the past solar wind. We were able to study the solar wind noble gas isotopes in the extraterrestrial materials using the novel analytical method. In the future, the quantitative analysis allows us to perform simultaneous multi-element isotope analysis and discuss the origin of the solar wind gas-rich samples using isotope ratios.
References: [1] Allègre et al. EPSL, 185, 49 (2001). [2] Sumino, JMSSJ, 63, 14 (2015). [3] Ebata et al. SIA, 44, 635 (2012). [4] Bajo et al. SIA, 48, 1190 (2016). [5] Tonotani et al. SIA, 49, 1122 (2016). [6] Nagata et al. APE, 12, 085005 (2019). [7] Bajo et al. SIA, 51, 35 (2019). [8] Bajo et al. GJ, 49, 559 (2015). [9] Wada et al. this session. [10] Otsuki et al. this session. [11] Obase et al. this session.