应用最小二乘法建立钾长石释光测年标准生长曲线

Establishing Standard Growth Curve(SGC) for Optical Dating of K-feldspar by Least Square Method

标准生长曲线(Standardised Growth Curve,SGC)法的提出为高效快速地测定释光样品的等效剂量(De)值提供了可能。不同实验室的放射源剂量率、操作流程、仪器误差等的不同会导致SGC参数的不同。运用最小二乘法标准化实验剂量校正后的信号Lri/Tri*De得到一条本实验室的标准生长曲线,用来快速得到等效剂量值。通过R软件实现了最小二乘法标准化过程,建立了50、100、150、200、250℃激发温度下的钾长石的标准生长曲线,分析发现250℃下的SGC收敛性最好,由于此温度下的信号衰退率可忽略不计,因此,我们用250℃激发温度下的SGC方程来估计样品的等效剂量。比较250℃SGC De和250℃MET-pIRIR De的一致性,发现在0～500 Gy范围内用SGC法估计的De和MET-pIRIR法估计的De非常接近,表明了此范围内SGC法的可靠性,而在>600 Gy范围内出现较大差别。一方面,此范围内用于拟合SGC的数据点较少导致高剂量区域内拟合的方程参数不够准确;另一方面,600 Gy与SGC对应的饱和剂量水平值844.5 Gy已经接近,所以在>600 Gy区域测出的De很可能出现较大偏差。因此需在今后工作中逐步积累更多样品,完善SGC参数,使其也能胜任较老年龄样品。

The standard growth curve( SGC) provides a possible method for obtaining the De value of the sample efficiently and quickly. However,due to the radiation dose rate,operating procedures and instrument error,etc.,each laboratory should develop their own SGC which has unique parameters. In this study,SGC is a standard growth curve obtained by using the least squares method to standardize the test dose corrected signal Lri/T ri* De. It is used to quickly get the equivalent dose De value of the sample. The least square normalization process was realized by the R software;and the standard growth curve of K-feldspar was established at 50,100,150,200,250 ℃. It is found that the SGC has the best convergence at 250 ℃;and the signal fading rate is negligible at this temperature.Therefore,we estimate the equivalent dose of the sample by using the SGC function at 250 ℃. By comparing the consistency of 250 ℃ SGC De and 250 ℃ MET-pIRIR De,it is found that in the dose range of 0-500 Gy the obtained De values are well consistent by SGC and MET-pIRIR methods,which indicates the reliability of the SGC method in this range. There are obvious differences in the higher dose range( >600 Gy) compared to the MET-pIRIR results. The insufficient number of older samples used to fit SGC in this study leads to the function parameters is not accurate enough in the high dose region. On the other hand,600 Gy is close to the saturation dose level of 844.5 Gy,so the De measured is likely to have a large deviation in the region of >600 Gy. It is necessary to gradually accumulate more samples to improve the SGC parameters in the future work.