Rubidium/Strontium Dating of Meteorites

The study of the rubidium/strontium isotopic ratios in a set of meteorite samples shows the general approach to this kind of radioactive dating. The isotope ⁸⁷Rb decays into the ground state of ⁸⁷Sr with a half-life of 4.7 x 10¹⁰ years and a maximum b^- energy of 272 keV. ⁸⁶Sr is of non-radiogenic origin and can be used as a reference concentration to imply the original concentration of ⁸⁷Sr.

对一组陨石样品中 rubidium/strontium 同位素比值的研究展示了这种放射性鉴年法的一般方法。87Rb 衰变成 87Sr 的基态，半衰期为 4.7 x 10 10 年，最大 β 能量为 272 keV。86Sr 来自非放射性来源，可以作为参考浓度，用来推断原始 87Sr 浓度。

From an example by Jelley, the following five chondritic meteorites are reported to have the following proportions of the rubidium and strontium isotopes:

根据Jelley的一个例子，以下五种球粒陨石的铷和锶同位素比例如下：

这些数据如下面所示是用Excel表格绘制的。

The age consistent with the slope of this plot can be calculated in a way which makes use of the non-radiogenic ⁸⁶Sr as a reference. The slope obtained was m=0.0676, using the point-slope form of a line, y = mx + b, and the corresponding age is 4.6 x 10⁹ years. The intercept b = 0.70 suggests that these values for isotopic abundances are consistent with an original strontium isotope ratio ⁸⁷Sr/ ⁸⁶Sr = 0.7 .

这种图的斜率与年龄一致的值可以通过利用非放射性⁸⁶Sr作为参考来计算。得到的斜率是m=0.0676，使用直线的点斜式y = mx + b，相应的年龄是4.6×10⁹年。截距b=0.70表明这些同位素丰度的值与原始锶同位素比值⁸⁷Sr/⁸⁶Sr=0.7是一致的。

While the consistency is remarkable, there are uncertainties. A glance at the plot above shows that the Homestead meteorite is a bit off the line with the others. In fact, if just an average of the point-to-point slopes for all the data points is used, including the Homestead meteorite, an age of 4.7 billion is obtained, showing that there is a significant uncertainty in the dates obtained. The 4.6 billion year value was obtained by eliminating the Homestead meteorite, since that appeared to give a more consistent slope for the curve. This is all the data I have about these particular samples - comments about this scenario are invited.

尽管一致性相当显著，但仍存在一些不确定性。看一下上面的图表可以发现，Homestead陨石略微偏离了其他点的连线。事实上，如果使用所有数据点之间的点对斜率的平均值，包括Homestead陨石，会得到47亿年的年龄，这表明所获得的年代存在显著的不确定性。而46亿年的数值则是通过排除Homestead陨石得到的，因为这样似乎能更一致地拟合曲线。这就是我关于这些样品的全部数据——欢迎对这一情景提出评论。