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初始钍的校正是不纯沉积碳酸盐230Th 234U 238U测年的一个重要方面,洞穴石笋初始Th校正通常采用230Th/232Th的原子比值为(4. 4±2. 2)×10-6。多年来4种不同的等时线方法应用到不纯碳酸盐测年初始Th的校正中,其中全样品的等时线方法是目前公认的较为完善的一种方法。通过测定云南同一石笋2个不同层位的9个样品的U、Th同位素组成,并进行等时线分析,结果表明2层样品初始钍230Th/232Th原子比值分别为(3. 5±2. 8)×10-6和(10. 6±2. 2)×10-6,这说明即使在同一地区,由于其混入Th来源的复杂性,230Th/232Th初始比值在同一样品不同层位仍可能有较大的差异,因此不能够完全采用单一层位等时线获得的初始值对整个样品进行校正。考虑到在实验测量过程中,232Th含量的过高对于230Th的准确测定也有很大的影响,应尽量选择纯净石笋样品进行测年研究,在样品的选择和前处理过程中就减少初始钍的影响,这对获得高精度的测年结果有着重要的意义。
The initial thorium correction is an important aspect of the 230Th 234U 238U dating of impure carbonate. The initial Th correction for cave stalagmites usually uses an atomic ratio of 230Th / 232Th (4.4 ± 2.2) × 10-6. Over the years, four different isochronal methods have been applied to calibrate the initial Th dating of impure carbonates. The isochrone method of all samples is now a well-established method. By measuring the U and Th isotopic compositions of nine samples from two different layers of the same stalagmite in Yunnan Province and carrying out isochronous analysis, the initial thorium 230Th / 232Th atomic ratios of the two samples were (3. 5 ± 2. 8 ) × 10-6 and (10.6 ± 2.2) × 10-6, indicating that even in the same area, due to the complexity of their mixed source of Th, the initial ratio of 230Th / 232Th may still exist in different layers of the same sample Therefore, the entire sample can not be completely corrected by using the initial values obtained by a single-layer isochrone. Taking into account the experimental measurement process, 232Th content too high for accurate determination of 230Th also have a great influence, we should try to select pure stalagmite samples dating study, sample selection and pretreatment to reduce the impact of the initial thorium , Which is of great significance for obtaining high-precision dating results.