ESR测年研究中人工辐照吸收剂量的确定

DOSE DETERMINATION IN ESR DATING RESEARCH

在ESR测年研究中,被测样品的年代是通过样品的古剂量与样品所接受的年剂量的比值得到的。古剂量则是在实验室内经放射性源的人工辐照模拟自然界的ESR信号增长情况获得的。因此,人工辐照样品吸收剂量的确定成为影响测年可靠性的一个重要因素。目前一般有两种方法确定测年样品的人工辐照吸收剂量值一种是剂量率法,即在辐照前利用标准剂量体系对辐照位置的吸收剂量率进行校准,然后在同一位置辐照被测样品,通过校准得到的吸收剂量率和辐照时间确定样品的吸收剂量,通常所用的标准剂量体系为硫酸亚铁剂量计;另一种是伴随法,即在辐照前将参考剂量计与被测样品一起放到辐射场中辐照,参考剂量计一般采用经标准剂量体系(如硫酸亚铁剂量计或量热计等)校准过的丙氨酸剂量计,照后由参考剂量计直接给出被测样品的吸收剂量。文中就确定吸收剂量的两种方法的可靠性进行了探讨,并利用两种类型的丙氨酸剂量计通过伴随法测定了被测样品的吸收剂量。结果表明,根据目前ESR测年研究中地质样品人工辐照的实际情况,利用伴随法通过参考剂量计确定被测样品的吸收剂量更为实用与可靠。

In ESR dating, the age is given by the ratio of paleo-dose to annual dose. Generally, the paleodose is obtained by linear extrapolation in regeneration or additional irradiation method. Therefore, dose determination in manual irradiation becomes one of the important factors that effect reliability of the dating results. Usually, there are two ways to determine the dose of manual irradiation： one is called dose rate method, which calibrates the dose rate of the position by standard dosimeter before dating sample irradiation at the same position. Dose will be determined by the dose rate and irradiation time of the sample. In this method, Fricke dosimeter is usually used as standard dosimeter; the other is called concomitant method, which puts reference dosimeter together with the dating sample to the position before irradiation. They will be irradiated simultaneously and the dose will be given by the reference dosimeter. In this method, alanine dosimeter is generally used as the reference dosimeter. In the paper, these two methods are discussed. Two types of alanine dosimeter are used as reference dosimeters： one is pellet alanine dosimeter, the other is alanine film dosimeter. We use dose rate results that were calibrated one year ago to evaluate the current dose rates. Irradiation time is de- termined according to the nominal dose and the dose rate. However, the actual dose was determined by the alanine dosimeter that was irradiated with the dating sample together. Since it is not practical to calibrate the dose rate every time for every position before dating sample irradiation, the concomitant method that uses alanine dosimeter as reference to be irradiated with the dating sample together will be more practical and reliable compared with the dose rate method.