The Concentration Determination for High Atomic Number Elements by <gamma>-Ray Excited DX-Ray Spectrometry

为了测定高Z元素的浓度，本文研究了Cs-<gamma>137源（半衰期30.17年，662 KeV<gamma>射线）的KX射线荧光技术，用高纯锗半导体探测器进行非色散光谱测定。用这种技术可以分析容器或管道中的样品，Cs-137<gamma>射线有足够的能量激发高Z元素的KX射线，但<gamma>在样品中会产生大量的康普顿散射射线，而且KX射线与样品散射辐射的比值要大，才能有足够的精度。在该方法中，通过改变源、样品和X射线探测器之间的几何关系来减少散射辐射，以提高比值，样品的密度、粒度、基体成分等条件的变化对浓度-KX射线/康普顿计数比值的特征校准曲线有很大影响。对于粉末、水溶液和所有含W、Pb或U超过几个wt%的合金试样，300秒测量的相对精度小于3%。

In order to determine the concentration of high Z elements, KX-ray fluorescence technique by using a Cs-137 <gamma>-ray source (half-life 30.17 years, 662 KeV <gamma>-ray) with non-dispersive spectrometry using a high pure germanium semiconguctor detector is investigated. It is possible with this technique to analyse the specimens enclosed in containers or pipe lines.The Cs-137 <gamma>-ray has enough energy to excite the KX-rays of high Z elements, however considerable amount of Compton scattered <gamma>-rays in specimens is produced, and large ratio of the KX-rays to the scattered radiation from specimens is required to have sufficient accuracy. In this method, the scattered radiation should be reduced to improve the ratio by setting up the geometry between the source, specimen and X-ray detector.The variation of specimen conditions such as density, particle size, matrix composition affect much on the characteristic calibration curves related to the concentration vs. KX-ray/Compton count ratio. The 300 second measurement allows the relative precision of less than 3% for powder, aqueous solution, and all alloy specimens containing more than a few wt% W, Pb or U.