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

铁轻元素化合物的核共振散射和X射线衍射研究对地核组成的制约地核轻元素组成一直是地球内部研究中的一个谜。轻元素的存在首先是从相应条件下核心相对于纯铁的密度亏损和速度过剩推断出来的。 为了测试相互竞争的核心组成模型，我们需要准确了解各种轻元素对铁的密度和速度的影响，作为压力和温度的函数。以前的工作已经将硫和碳列为核心中主要轻元素的主要候选者，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。研究人员将把数据覆盖范围扩展到Mbar区域，最高可达1700 K，在与现有纯铁测量相同的压力和温度范围内。X射线衍射和核共振散射-这两种已建立的同步辐射技术-将被应用于确定相稳定性，状态方程和部分声子态密度的富铁化合物含有硫和碳的量是在地球核心的估计范围内。新的数据将使研究小组能够探索硫和碳对铁的密度和声速的影响，这是以前未知的压力-温度部门。他们将能够对描述含硫或含碳核心情景的候选模型进行严格的测试。这项研究将提供有关富铁合金在高压和高温下的性质以及行星核心性质的基本新知识。

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.