化石电子自旋共振(ESR)测年等效剂量标准生长曲线的构建

目前在化石ESR测年工作中主要采用Gamma源(⁶⁰Co或¹³⁷Cs)对样品进行辐照，由于这种辐照源放射性较强对环境和人体健康存在安全隐患，因此只有少数专业机构有资格开展Gamma辐照工作，加之辐照过程较高的时间和经济成本，在很大程度上制约了ESR测年方法的应用。为此本研究对十余个已开展过测年工作的考古遗址的化石样品进行了再分析，并尝试建立牙釉质等效剂量标准生长曲线，在不对样品进行辐照的前提下通过测定自然样品的ESR信号强度来获得其等效剂量。研究显示对于较年轻的化石样品，采用牙釉质标准生长曲线与附加剂量法获得的等效剂量值较一致，但对较老的样品(等效剂量D_e>2000 Gy)两种方法得到的等效剂量值存在明显差异。研究表明通过非辐照的方式获得样品的D_e值具有可行性但目前建立的标准生长曲线尚有待完善，同时探讨了采用标准生长曲线方法对开展化石ESR测年工作的潜在优势。

Establishment of the standardised growth curves for ESR dating of fossil teeth

The Gamma irradiation source(60Co and 137Cs)are widely used in the fossil electron spin resonance(ESR)dating for sample irradiation. However, limited institutions are qualified for the gamma irradiation job because of its safety hazard to the environment and human health. Moreover, the time and financial cost of irradiation severely restrict the work of equivalent dose(De)estimation in fossil ESR dating. In this study, we attempt to establish a standardised growth curve(SGC)of tooth enamel based on 46 fossil samples from 13 prehistorical sites we dated before by ESR method, and explore the possibility of determining the De without sample irradiation by measuring the natural signals. Another 10 fossil samples which not involved to build the SGC were used to compare the De results obtained by SGC and additive dose method. Our study indicated that the De obtained by SGC were close to the ones extrapolated from the additive dose method for the young samples with relative low De values. However, the apparent discrepancy of De values determined by the two methods were observed for the old samples with De>2000 Gy. This result may attribute to the De values used to establish the SGC were obtained by single saturation exponential(SSE)fitting function which was proved less suitable for the De determination than the double saturation exponential(DSE)function for the old samples. Although the precision of De determination by the SGC method cannot reach the additive dose method at the moment, it does show some potential advantages: (1)Help to determine the Dmax value used for sample irradiation. (2)Quick identify the intrusive samples from the younger or older layers. (3)Less sample needed for ESR analysis which makes the dating of small mammalian and precious human fossils possible.