在弱α放射性的测量工作中,测量的精密度和所需的测量时间,常是由测量装置的本底所决定的。对一台测量装置,只要首先分析出本底的来源,然后采取相应降低本底的措施,常可显著地改善其性能。本文以一台常用的Π-349-2型闪烁计数器为例,说明这一问题;并讨论低本底的获得与保持的一般方法。 In the measurement of weak α-radioactivity, the precision of measurement and the required measurement time are often determined by the background of the measuring device. For a measuring device, the performance of a measuring device can often be significantly improved by first analyzing the source of the background and then taking measures to reduce the background accordingly. This article uses a common Π-349-2 scintillation counter as an example to illustrate this issue; and discusses the general approach to obtaining and maintaining a low background.