液闪分析中闪烁体积对各种核素测定的影响

摘要

Scintillation volume,as well as quench,is an important factor in change of counting efficiency for liquid scintillation counting (LSC).Various representative radionuclides have been determined in two liquid scintillation counters,with the discrimination between the influence of scintillation volume and that of quench.The influence of scintillation volume is very little on the counting efficiency of α particles or high energy β particles.The wall effect resulting from small scintillation volume changes the shape of LSC spectrum,but has little influence on the counting efficiency.The influence of scintillation volume is remarkable on the counting efficiency of γ rays or low energy β particles.The quench with the same level has greater influence on the counting efficiency of the sample with larger scintillation volume.When a quench correction curve is used to calculate the counting efficiency or a curve of "optimum PSA-quench index" is used to set the parameter of α/β discrimination,in order to minimize the measurement uncertainty,the sample to be determined should have the same scintillation volume in the vial with the same size as the quenching standards,no matter what quench index is applied.%除了淬灭以外,闪烁体积是影响液闪计数效率的另一个重要因素.采用可区分闪烁体积影响和淬灭影响的实验方法,在两种液闪仪上测定了多种代表性核素.结果表明:在实验淬灭水平范围内,闪烁体积对α粒子和高能β粒子的计数效率影响很小,小闪烁体积测量时的壁效应仅仅影响液闪谱图的形状,对计数效率的影响可以忽略;闪烁体积对γ射线和低能β粒子的计数效率影响很大,相同水平的淬灭对闪烁体积较大样品的计数效率影响较大.在用淬灭校正曲线计算计数效率或用“最优PSA-淬灭指数”曲线设置a/β甄别参数时,为了减小测量误差,不管采用什么淬灭指数,待测样品都需要与淬灭标准样品保持相同的闪烁体积和闪烁瓶尺寸.