Over the past few decades, the (U-Th)/He geochronological method on goethite has been more and more applied to date laterite formation and evolution or ore-deposit formation. However, questions remain on possible He loss by diffusion due to the polycrystalline structure of goethite and associated underestimation of the goethite crystallization date given by the (U-Th)/He age. Prior studies estimated helium loss in goethite to range from 2 to 30%, but no relation or models have been produced to explain such values. To clarify the situation, we firstly performed a complete review of experimental He diffusion data in natural goethite, that reveals the link between activation energy and He loss with the damage dose. To understand He diffusion behavior in goethite and model the He loss, natural defect and alpha damage as well as the chemical composition and growth structure effect on He diffusion have been investigated thanks to a multi-scale study. We used numerical simulations combining the Density Functional Theory (DFT) at the atomic scale and Kinetic Monte Carlo (KMC) simulations at the macroscopic scale. We found that He diffusion is purely anisotropic along the preferential elongated axis (i.e., b-axis) and He leaks out easily in defect-free goethite and Al-goethite. The consequence of this anisotropy is that crystallographic defects and alpha damage strongly lower the He diffusivity in goethite and Al-goethite by obstructing the diffusion channel or trapping He along the b-axis. Defect and damage impact on He diffusion is even larger for Al-goethite. The obtained He diffusion parameters for goethite containing defect and damage are similar to the activation energy and He diffusional loss obtained in natural goethite from the literature. We demonstrate the systematic dependence of the diffusion coefficient with damage dose and the impact of Al on He retention. He atoms are retained only at the favor of obstructions blocking the diffusion and vacancies trapping them in the goethite structure. The consequence of the diffusive behavior is that a part of He diffuses out of the crystal until sufficient damage accumulated along the b-axis. The diffusion domain size is the channel length along the b-axis rather than the whole crystallite size. To correct the He loss this study proposes estimation of the He retention and needed corrections for different types of goethite.

近几十年来，针铁矿的(U-Th)/He年代学方法越来越多地应用于确定红土形成演化或矿床形成的年代。然而，由于针铁矿的多晶结构以及 (U-Th)/He 年龄给出的对针铁矿结晶日期的相关低估，关于扩散可能损失 He 的问题仍然存在。先前的研究估计针铁矿中的氦损失在 2% 到 30% 之间，但没有产生任何关系或模型来解释这些值。为了澄清这种情况，我们首先对天然针铁矿中的 He 扩散实验数据进行了全面审查，揭示了活化能和 He 损失与损伤剂量之间的联系。为了了解针铁矿中的 He 扩散行为并模拟 He 损失，通过多尺度研究，研究了自然缺陷和α损伤以及化学成分和生长结构对He扩散的影响。我们使用结合原子尺度的密度泛函理论 (DFT) 和宏观尺度的动力学蒙特卡罗 (KMC) 模拟的数值模拟。我们发现 He 扩散沿优先拉长轴是纯各向异性的（即，b轴）和 He 在无缺陷的针铁矿和铝针铁矿中容易泄漏。这种各向异性的结果是晶体缺陷和 α 损伤通过阻碍扩散通道或沿b捕获 He 强烈降低针铁矿和铝针铁矿中的 He 扩散率。-轴。铝针铁矿的缺陷和损伤对氦扩散的影响更大。得到的含有缺陷和损伤的针铁矿的 He 扩散参数与文献中在天然针铁矿中获得的活化能和 He 扩散损失相似。我们证明了扩散系数与损伤剂量的系统依赖性以及 Al 对 He 保留的影响。He 原子仅在有利于阻碍扩散的障碍物和将它们困在针铁矿结构中的空位的情况下才被保留。扩散行为的结果是一部分 He 扩散出晶体，直到沿b轴累积足够的损伤。扩散域尺寸是沿b的沟道长度轴而不是整个微晶尺寸。为了纠正 He 损失，本研究提出了对不同类型针铁矿的 He 保留和所需校正的估计。