Irradiation of Low Temperature Solids: Physical Mechanisms and Astrophysical Implications

低温固体辐照：物理机制和天体物理意义

• 批准号: 0098523
• 负责人: Robert Johnson
• 金额: $ 14.63万
• 依托单位: University of Virginia Main Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-08-01 至 2005-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0098523&HistoricalAwards=false
• 关键词: Irradiation; Low; Temperature; Solids; Physical

AST 0098523JohnsonDr. Robert Johnson, at the University of Virginia, will continue a research program to model the radiolysis and photolysis of low temperature solids in the outer Solar System and the interstellar medium (ISM). Irradiation by charged-particles or UV-photons of ice, molecules trapped in an ice matrix or hydrated minerals can determine the ambient neutral envelopes and the spectral properties of outer solar system satellites and of grains in the ISM. An understanding of the interaction of energetic ions, electrons and UV -photons with surfaces is needed to interpret many recent observations .A large body of laboratory data now exists on the sputtering and decomposition of low temperature condensed-gas solids. This data set has some inconsistencies, as well as large gaps in the materials studied and in the incident particle type and energies studied. It has only recently been shown that the long-ignored energetic electrons are important when describing the alteration of icy satellite surfaces. Therefore, Dr. Johnson will carry out a materials-based calculation program to model the available data and then use the results to expand the applicability of these data. His recent molecular dynamics calculations of energy transport during the sputtering of ices will be used to describe the sputtering of volatile and refractory species trapped in an ice matrix. In addition, he will incorporate and test those solid-state chemistry models that have been proposed for the production and desorption of new molecules due to irradiation of ice. The goal is to be able to calculate results for all charged particle types and energies, including cluster impact, for application to sputtering of a grain in the ISM, a ring particle, or a satellite regolith with a grain size and porosity much different than that used in laboratory studies. Such work is possible due to the rapid improvements in the computational tools available in materials science and because there exists an extensive set of data that can be used to test and calibrate these methods for the materials of interest in the outer Solar System and the ISM . Monte Carlo (MC) particle transport codes, which determine the distribution of energy deposition in a material, will be used along with molecular dynamics (MD) models and a continuum model to describe the energy transport and sputtering. The suggested chemical pathways for radiolysis and photolysis will be integrated in the MD model in order to describe aspects of the radiation-induced solid-state chemistry occurring in ice. Finally, Dr. Johnson will continue to assemble laboratory data from the large number of groups studying ion, electron and photon-induced sputtering and implantation and then incorporate these data into the proposed calculations .***

AST 0098523约翰逊博士弗吉尼亚大学的罗伯特约翰逊将继续进行一项研究计划，模拟太阳系和星际介质（ISM）中低温固体的辐解和光解。 冰的带电粒子或紫外光子、冰基质中捕获的分子或水合矿物的辐射可以确定环境中性包络以及外太阳系卫星和ISM中谷物的光谱特性。 为了解释最近的许多观测结果，需要了解高能离子、电子和紫外光子与表面的相互作用。现在有大量关于低温凝气固体的溅射和分解的实验室数据。这一数据集有一些不一致之处，以及在研究的材料和入射粒子类型和能量研究的大差距。 直到最近才表明，长期被忽视的高能电子在描述冰冷的卫星表面的变化时是重要的。因此，约翰逊博士将执行一个基于材料的计算程序，对可用数据进行建模，然后使用结果来扩展这些数据的适用性。他最近的分子动力学计算的能量传输过程中溅射的冰将被用来描述溅射的挥发性和难熔的物种被困在冰矩阵。此外，他将结合和测试那些已经提出的固态化学模型，用于由于冰的照射而产生和解吸新分子。目标是能够计算所有带电粒子类型和能量的结果，包括集群的影响，适用于溅射的一个晶粒在ISM，一个环粒子，或卫星风化层的粒度和孔隙度远远不同于在实验室研究中使用的。由于材料科学中可用的计算工具的快速改进，并且因为存在大量的数据可以用于测试和校准这些方法，用于外太阳系和ISM中感兴趣的材料，这样的工作是可能的。 蒙特卡罗（MC）粒子输运程序，它确定了能量沉积在材料中的分布，将沿着分子动力学（MD）模型和连续模型来描述能量传输和溅射。建议的辐射分解和光解的化学途径将被集成在MD模型，以描述辐射诱导的固态化学发生在冰的方面。最后，约翰逊博士将继续收集大量研究离子、电子和光子诱导溅射和注入的小组的实验室数据，然后将这些数据纳入拟议的计算中。