The initial abundance of plutonium-244 in the solar system evaluated by using meteoritic zircons

• Project/Area Number: 17K14421
• Research Category: Grant-in-Aid for Young Scientists (B)
• Allocation Type: Multi-year Fund
• Research Field: Geochemistry/Cosmochemistry
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: Haba Makiko 東京工業大学, 理学院, 助教 (30598438)
• Research Collaborator: Nagao Keisuke ; Yamaguchi Akira ; Wotzlaw Jörn-Frederik
• Project Period (FY): 2017-04-01 – 2019-03-31
• Project Status: Completed (Fiscal Year 2018)
• Budget Amount: ¥3,640,000 (Direct Cost: ¥2,800,000、Indirect Cost: ¥840,000); Fiscal Year 2018: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2017: ¥2,210,000 (Direct Cost: ¥1,700,000、Indirect Cost: ¥510,000)
• Keywords: 消滅核種 / プルトニウム / 初生存在度 / 隕石ジルコン / 希ガス分析 / 81Kr-Kr / 宇宙線照射年代 / プルトニウム-244 / 高精度U-Pb年代分析 / (U-Th)/He年代 / プルトニウム244 / 年代測定

Outline of Final Research Achievements

Plutonium-244 is an extinct nuclide and does not exist in the current solar system. However, its existence in the early solar system has been proved by the detection of spontaneous fissiogenic Xe derived from 244Pu in meteorites. The initial 244Pu/238U ratio in the solar system is important to estimate the period from nucleosynthesis for U and Pu to the birth of the solar system. In this study, we attempted to determine a precise initial 244Pu/238U ratio by measuring the Xe isotope compositions and U-Pb date of zircons separated from a mesosiderite. As a result, the initial 244Pu/238U ratio determined in this study is 0.012 ± 0.004, which is more precise than those reported in the previous works.

Academic Significance and Societal Importance of the Research Achievements

本研究では、世界で初めて隕石ジルコンを用いて太陽系の初生244Pu/238U比を見積もることに成功した。今回決定された初生244Pu/238U比は、過去の研究と比べ圧倒的に精度が良い。また、244Pu/238U比を算出するために用いたジルコンのU濃度は分析方法の改良によって誤差を小さくすることが可能であるため、将来的に初生244Pu/238U比の精度を向上させることは十分に可能である。今後、得られた太陽系の初生244Pu/238U比を元素合成モデルと比較することにより、太陽系のUおよび超ウラン元素を生成した元素合成の恒星におけるサイトや太陽系形成までの期間の見積もりが可能になると予想される。

Research Products

• [Journal Article] Trace element composition and U-Pb age of zircons from Estherville: Constraints on the timing of the metal-silicate mixing event on the mesosiderite parent body (2017)
  • Author(s): Haba Makiko K.、Yamaguchi Akira、Kagi Hiroyuki、Nagao Keisuke、Hidaka Hiroshi
  • Journal Title: Geochimica et Cosmochimica Acta Volume: 215 Pages: 76-91
  • DOI: 10.1016/j.gca.2017.07.028
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Presentation] 消滅核種Pu-244の太陽系初生存在度 (2018)
  • Author(s): 羽場麻希子、長尾敬介、Jorn-Frederik Wotzlaw、山口亮
  • Organizer: 2018年度日本地球化学会第65回年会
• [Presentation] 隕石ジルコンの複合的年代学 (2018)
  • Author(s): 羽場麻希子、長尾敬介、Jorn-Frederik Wotzlaw、山口亮
  • Organizer: 2018年度日本地球化学会第65回年会
• [Presentation] Multi-chronology of meteoritic zircon and the initial abundance of plutonium-244 in the solar system (2018)
  • Author(s): M. K. Haba, K. Nagao, J. F. Wotzlaw, A. Yamaguchi
  • Organizer: The 81st Annual Meeting of The Meteoritical Society
  • Int'l Joint Research
• [Presentation] メソシデライト母天体におけるメタルシリケイト混合年代の決定 (2017)
  • Author(s): 羽場 麻希子、山口 亮、Lai Yi-Jen、Wotzlaw Jorn-Frederik、Schonbachler Maria
  • Organizer: JpGU-AGU Joint Meeting 2017
  • Invited
• [Presentation] Formation age of mesosiderites (2017)
  • Author(s): Makiko K. Haba, Akira Yamaguchi, Yi-Jen Lai, Jorn-Frederik Wotzlaw, and Maria Schonbachler
  • Organizer: The Eighth Symposium on Polar Science
  • Int'l Joint Research