The activity measurement of 88 Y by 4π(PPC)X-γ digital coincidence counting method was introduced in this paper .In order to improve detection efficiency of X ray , high pressure proportional counter was used .It is found that the argon methane gas has the advantage of high detection efficiency and low operating voltage by comparing the plateau curves of methane gas and argon methane gas .T he argon methane gas is chosen as the working gas .After the collection of original spectrum ,different γ windows were selected for the offline digital coincidence counting calculation , and the efficiency extrapolation values and the measurement uncertainty were analyzed .%本文介绍了采用4π（PPC ）X-γ数字符合测量装置绝对测量88 Y放射性活度的方法。为提高对X射线的探测效率，实验采用高气压正比计数器，测量比较了甲烷和氩甲烷作为其工作气体的坪曲线，后者具有探测效率高、起始坪电压低的优势，因此采用氩甲烷为工作气体。采集原始谱数据后，选择不同的感兴趣γ窗进行离线数字符合计算，并分析了效率外推的结果和测量的不确定度。
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