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

核共振散射和铁-轻元素化合物的x射线衍射研究对地核组成的限制地核的轻元素组成一直是地球内部研究中的一个长期未解之谜。在相应的条件下，相对于纯铁的密度缺陷和速度过剩，首先推断出了轻元素的存在。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铁的密度和速度的影响（作为压力和温度的函数）。尽管铁硫合金和铁碳合金的密度和声速数据仅限于室温和中压，但之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。研究人员将在现有纯铁测量的相同压力和温度范围内，将数据覆盖范围扩展到毫巴范围和1700k。x射线衍射和核共振散射——两者都是已建立的同步辐射技术——将被用于确定在地球核心估计范围内含有大量硫和碳的富铁化合物的相位稳定性、状态方程和部分声子状态密度。新的数据将允许研究小组在一个以前未知的压力-温度区域探索硫和碳对铁的密度和声速的影响。他们将能够对描述含硫或含碳岩心情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能以及行星核心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.