Constraints on core composition from nuclear resonant scattering and x-ray diffraction studies on Fe-light-element compounds

从核共振散射和X射线衍射研究铁轻元素化合物对核心成分的制约地核的轻元素组成在地球内部的研究中一直是一个长期存在的谜团。在相应的条件下，根据磁芯相对于纯铁的密度亏损和速度过剩，首次推断出轻元素的存在。为了测试相互竞争的核心成分模型，我们需要准确地了解各种轻元素对作为压力和温度函数的铁的密度和速度的影响。尽管铁硫和铁碳合金的密度和声速数据仅限于室温和中等压力，但之前的工作已将硫和碳列为核心主要轻元素的主要候选者之一。调查人员将把数据覆盖范围扩大到Mbar制度和高达1700K，范围与现有纯铁测量的压力和温度范围相同。X射线衍射和核共振散射--这两项都是公认的同步辐射技术--将被用来确定富铁化合物的相稳定性、状态方程和部分声子状态密度，这些化合物的硫和碳含量在地球核心的估计范围内。新的数据将使该团队能够探索硫和碳对铁的密度和声速的影响，这是一个以前未知的压力-温度区域。他们将能够对描述含硫或含碳核心场景的候选模型进行严格的测试。这项研究将为富铁合金在高压和高温下的性质以及行星核的性质提供基本的新知识。

Constraints on core composition from nuclear resonant scattering and x-ray diffraction studies on iron-light-element compoundsThe light element composition of the Earth's core has been a long-standing mystery in the study of the Earth's interior. The presence of light elements was first inferred from the density deficit and velocity excess of the core relative to that of pure iron under corresponding conditions. In order to test competing core composition models, we need accurate knowledge of the effects of various light elements on the density and velocities of iron as a function of pressure and temperature. Previous work has placed sulfur and carbon among the leading candidates for the principal light element in the core, even though density and sound velocity data for iron-sulfur and iron-carbon alloys are limited to room temperature and moderate pressures. The investigators will extend the data coverage into the Mbar regime and up to 1700 K, over the same pressure and temperature range of the existing measurements on pure iron. X-ray diffraction and nuclear resonant scattering - both established synchrotron radiation techniques - will be applied to determine the phase stability, equation-of-state, and partial phonon density-of-state of iron-rich compounds containing amounts of sulfur and carbon that are within the estimated range for the Earth's core. The new data will permit the team to explore the effects of sulfur and carbon on the density and sound velocities of iron in a previously uncharted pressure-temperature sector. They will be able to conduct stringent tests of candidate models describing sulfur-bearing or carbon-bearing core scenarios. This research will provide fundamental new knowledge about the properties of iron-rich alloys at high pressures and temperatures and the nature of planetary cores.