高浓铀年龄的γ能谱法非破坏性分析

Age Determination of Highly Enriched Uranium Based on Nondestructive Gamma-Ray Spectrometry

描述了一种采用HPGe探测器γ能谱法无损测量核材料铀样品并计算样品的生产（纯化）年龄与同位素丰度的方法。该方法不需要其他任何标准源或参考源,对样品的形态（固体、液体）和形状没有限制,由铀样品自身所含多γ射线核素的γ能峰来刻度相对峰效率曲线,由能峰计数率、相对效率、γ射线发射概率等参数确定铀同位素的比值,由^234U与其衰变子体214Bi的活度比值计算其生产年龄。对一个铀总量约5g、^235U浓缩度约90%的24mL液体铀样品,用两套HPGe探测器分别测量不同能区范围的γ能谱：在平面型探测系统获取的低能区能谱中,用^235 U的γ能峰刻度相对峰效率曲线,计算了^234 U、^228Th（232 U子体）与235 U的相对比值;在同轴型探测系统获取的高能区能谱中,用^228 Th及其子体的γ能峰刻度相对峰效率曲线,计算^238 U、^214Bi与^228Th的相对比值,综合计算得到铀样品生产年龄（-32a）及铀同位素丰度,并与样品经过放化分离后,质谱法测量得到的结果进行了比较,生产年龄与丰度比偏差均在5%以内符合。

A method for the age and isotopic abundances determination of highly enriched uranium samples by gamma spectrometry is described.No standard or reference source is required and no form or shape limitation is imposed on the sample.Relative activity ratios between uranium isotopes and ratios between ^214Bi（a daughter in 234 U decay chain）and ^234U,as well as the age,are determined using relative peak efficiency curves constructed with the sample itself.The spectra in different energy regions of a 24 mL liquid sample with 5g uranium and nearly 90%enrichment of ^235U were acquired with two HPGe detectors,the planar one used to obtain the lower energy relative peak efficiency curve by fitting with peaks of ^235U to determinate the activity ratios of ^234U and ^228Th（daughter of 232 U）to ^235U,the coaxial one used to obtain the higher energy relative peak efficiency curve by fitting with the peaks of ^228Th and its daughters to determinate the activity ratios of ^238U and ^214Bi to ^228Th.The re-sults of age（-32a）and isotopic abundances for the sample were compared to those obtained by radiochemical-mass spectrometry,showing a bias less than 5%.