本文通过控制变量的对比实验方法，系统研究了NaI( Tl) 谱仪中反散射峰产生的原因以及影响其大小的因素. 结果发现衬底材料、衬底厚度、源仪距、源衬底距、闪烁体的包装材料和闪烁体的尺寸均对反散射峰有不同程度的影响. 经过对比分析，找到了几种抑制反散射峰的简便易行的实验方法.

In Millikan's oil-drop experiment，if the oil drop is chosen too small，it shows obvious Brownian motion，which causes the measured dropping time to deviate from the ideal dropping time. In this article，through practical experiment and theoretical study，the stochastic differential equation of the movement of the oil drop is established by solving the Langevin equation. By introducing single and multiple time deviation，both the Brownian motion and the time deviation are quantitatively analyzed. As being indicated by the result，when the oil drop is relatively small，the influence of Brownian motion should be taken into account because of the limit of experiment times.