Etching of fission tracks in monazite: Further evidence from optical and focused ion beam scanning electron microscopy
Etching of fission tracks in monazite: Further evidence from optical and focused ion beam scanning electron microscopy
复制标题
独居石中裂变径迹的蚀刻：来自光学和聚焦离子束扫描电子显微镜的进一步证据
作者：
Sean Jones;B. Kohn;A. Gleadow
摘要 对澳大利亚维多利亚独居石进行了一系列实验，以进一步了解其裂变径迹蚀刻特性。在 90 °C 下使用 6 M HCl 蚀刻剂，晶体 (100) pinacoid 面上的 SEM 图像显示出蚀刻良好的菱形自发裂变轨道开口。平行于晶体 c 轴和 b 轴的平均菱形蚀刻坑直径 Dpc 和 Dpb 分别为 0.81 ± 0.20 μm 和 0.73 ± 0.26 μm。 (100) 面上的角分布实验发现，自发裂变径迹最初是各向异性蚀刻的，优先在与晶体 c 轴成 90° 的方位角处显示，直至蚀刻约 60 分钟。然而，随着蚀刻的继续，分布逐渐变得更加均匀，并且到 90 分钟时基本上是各向同性的。两种实验方法确定了蚀刻剂沿植入的 252Cf 裂变径迹的长度渗透的速率。这涉及应用聚焦离子束扫描电子显微镜 (FIB-SEM) 逐步研磨成轻微蚀刻的独居石晶体，然后采用蚀刻-退火-蚀刻方法。结果表明，在最初的几分钟内，至少大部分潜在裂变径迹的可蚀刻范围被 6 M HCl 蚀刻剂渗透。持续蚀刻至 5 分钟表明，轨道蚀刻朝着轨道末端减慢，但估计在 5-15 分钟后达到最大范围，这代表轨道的潜在部分在蚀刻剂温度下暴露于潜在退火的最长时间。考虑到独居石中注入的 252Cf 裂变径迹在 90 °C 下退火 1 小时后平均长度约为 4%（Jones 等人，2019），表明暴露于该温度的持续时间短得多，导致蚀刻期间裂变径迹长度减少不到约 1%。
Abstract A series of experiments on monazites from Victoria, Australia, is presented to further understand their fission track etching properties. Using a 6 M HCl etchant at 90 °C, SEM images on crystal (100) pinacoid faces reveal well-etched rhombic spontaneous fission track openings. Average rhombic etch pit diameters Dpc and Dpb, parallel to the crystallographic c- and b-axes are 0.81 ± 0.20 μm and 0.73 ± 0.26 μm, respectively. An angular distribution experiment on (100) faces found that spontaneous fission tracks initially etch anisotropically, being preferentially revealed at an azimuth of 90° to the crystallographic c-axis up to ~60 min of etching. As etching continues, however, the distribution becomes progressively more uniform and is essentially isotropic by 90 min. Two experimental methods determined the rate at which the etchant penetrated along the lengths of implanted 252Cf fission tracks. This involved the application of a focused ion beam scanning electron microscope (FIB-SEM) to mill progressively into slightly etched monazite crystals followed by an etch-anneal-etch approach. Results indicate that at least the greater part of the etchable ranges of the latent fission tracks were penetrated by the 6 M HCl etchant within the first few minutes. Continued etching to 5 min indicates that track etching slows down toward the ends of the tracks, but the maximum ranges are estimated to be reached after 5–15 min, which represents the longest time the latent segments of the tracks are exposed to potential annealing at the etchant temperature. Taking into account that implanted 252Cf fission tracks in monazite anneal on average ~4% of their length at 90 °C after 1 h (Jones et al. 2019), suggests that a much shorter duration for exposure to this temperature causes less than ~1% of fission track length reduction during etching.