ESR法测定石笋类碳酸盐年代的研究

STUDY ON ESR DATING OF STALAGMITES

本文首先用ESR方法和U系法对照测定了石笋-Ⅰ的三个层位和一块钙华板的年代;在此基础上又测定出石笋-Ⅱ的五个层位年代,并亦用U系法对它们进行了验证,均取得一致的结果.考虑到次生碳酸盐形成之后,因U系不平衡,其内年剂量是变化的,故在用α能谱仪分析出U含量和^(234)U/^(238)U之后,再用计算机求其平均内年剂量.本文实验表明,用I=Imax[1-e^(-α/I)_(max)^(AD+Q)]来描述ESR信号Ⅰ随辐照剂量Q增长的全过程是合理的.当1/Imax较小时,用简单的直线外推即可得到可信的AD值;而当I/Imax较大时,须对-Ln(1-I/Imax)=α/Imax(AD+Q)作线性拟合才能获得合理的AD值.

The ages of three horizons in stalagmite-Ⅰ and one travertine plate are determined by using both ESR and U-series methods for comparison, followed by the dating of five horizons in stalagmite-Ⅱ which is also checked by U-series. The results are in good agreement. Since the inner annual dose is variable because of the disequilibrium of the U-series after the formation of secondary carbonates, the average inner annual dose of the samples has been calculated on computer after analyzing U content and U-234/U-238 ratio by α-energy spectrometer. It is obvious that the pattern of the response curve of the intensity of the ESR signal Ⅰ versus Rγ-irradiation of two stalagmites can be described reasonably by the following formula: I= Imax [ 1 -e-α/Imax(AD + Q) ]. If I/Imax is relatively small, linear extrapolation can be used to obtain the confident AD value, and if it is greater, the AD must be determined by linear fitting of the logarithmic equation -1n ( 1 - I/Imax ) =α/Imai( AD+Q) .