2003 Fiscal Year Final Research Report Summary
Study on the chemical evolution of planetary materials and the origin of meteorites inferred from variable analyses of cosmogenic nuclides
| Project/Area Number |
13440167
|
|---|
| Research Category |
Grant-in-Aid for Scientific Research (B)
|
| Allocation Type | Single-year Grants |
|---|
| Section | 一般 |
|---|
| Research Field |
地球化学
|
|---|
| Research Institution | Hiroshima University |
|---|
Principal Investigator |
HIDAKA Hiroshi Hiroshima University, Graduate School of Science, Professor, 大学院・理学研究科, 教授 (10208770)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
MIURA Yayoi University of Tokyo, Earthquake Research Institute, Research Associate, 地震研究所, 助手 (90282730)
|
|---|
| Project Period (FY) |
2001 – 2003
|
| Keywords | cosmogenic nuclide / neutron capture / meteorite / samarium / gadolinium / rare gas / isotope |
|---|
| Research Abstract |
Twelve martian meteorites, twelve aubrites (enstatite achondrites), eight fragments from the Jilin chondrite and fifteen lunar regoliths from Apollo 16 and 17 landing sites, were used in this research to study the interaction of cosmic rays with planetary materials. The samples were characterized from neutron-captured isotopic shifts of Sm and Gd, noble gasses isotopic variations, and abundances of cosmogenic isotopes such as ^<10>Be and ^<41>Ca.
New findings from this research are as follows : (1) Neutron captured Sm and Gd isotopes were found in six of twelve martian meteorites. Considering little correlation between cosmic-ray exposure ages estimated from noble gas analysis and irradiated neutron fluence from Sm and Gd isotopic measurements, some of martian meteorite experienced multi-stage irradiation. This reveals a possibility of pre-irradiation of the meteorites on Mars. (2) The calculated neutron fluences for some aubrites such as Pesyanoe and Khor Temiki show significant variations even in the same meteorite, which suggests the irradiation history in the regolith of the aubritic parent body. The systematic data between neutron fluences and cosmic-ray exposure ages suggest the subdivision of aubrites into subgroups with only space irradiation and a subgroup with regolith history. (3) Lunar regolith processes can be discussed from neutron stratigraphy of the Apollo-16 and 17 drill stems. The depth profiles of neutron fluences suggest that large mixing events occurred after deposition of the regoliths and that the regoliths consists mainly of two slabs.
|
