HREM STUDY OF IRRADIATION DAMAGE IN HUMAN DENTAL ENAMEL CRYSTALS
HREM STUDY OF IRRADIATION DAMAGE IN HUMAN DENTAL ENAMEL CRYSTALS
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DOI：
10.1016/0304-3991(91)90083-i
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发表时间：
1991-06-01
期刊：
影响因子：
2.2
通讯作者：
FRANK, RM
中科院分区：
文献类型：
--
作者：
BRES, EF;HUTCHISON, JL;FRANK, RM
在300和400keV的高分辨率电子显微镜(HREM)检查人类牙釉质晶体(主要由羟基磷灰石(OHAP)组成)过程中，观察到了几种现象：取向相关的损伤，表现为空洞质量损失或晶体结构均匀破坏，光束诱导的扩散在晶体表面产生突起，大块晶体重结晶，晶体周围基质的无机成分结晶。这些束流诱导晶体具有CaO结构。观察到的现象很可能是由于各种电子-晶体相互作用机制(弹道撞击损伤、电子激发、温升等)造成的。本文讨论了弹道过程对观测到的现象的贡献。碰撞的定量描述依赖于McKinley-Feshbach截面公式。这个表达式中出现的最小离子位移能是根据静电离子结合能和必要时的共价键能估算出来的。结果表明，300和400keV的入射电子可以有效地使羟基、钙和氧离子发生位移。因此，可以初步解释钙和氧离子从OHAP晶格内的起始位扩散而形成CaO晶体的原因。
Several phenomena have been observed during the examination of human dental enamel crystals (mainly constituted by hydroxyapatite (OHAP)) by high-resolution electron microscopy (HREM) at 300 and 400 keV: orientation-dependent damage in the form of mass loss from voids or uniform destruction of crystal structure, beam-induced diffusion creating outgrowths at the crystal surfaces, recrystallization of the bulk crystal and crystallization of the inorganic components of the matrix surrounding the crystals. These beam-induced crystals have the CaO structure. The phenomena observed are most likely due to various electron-crystal interaction mechanisms (ballistic knock-on damage, electronic excitations, temperature rise, etc.). In this paper, the contribution of the ballistic process to the phenomena observed is discussed. The quantitative description of the knock-on collisions rests on the McKinley-Feshbach cross-section formula. The minimum ion displacement energies which appear in this expression have been estimated on the basis of the electrostatic ion binding energies, and the covalent bond energies if required. It is shown that hydroxyl, calcium and oxygen ions can effectively be displaced by the incident 300 and 400 keV electrons. Thus, the formation of CaO crystals by the combination of calcium and oxygen ions diffusing from their initial sites inside the OHAP lattice can tentatively be explained.