In the Franck-Hertz experiment,the plate current oscillating curve suddenly rises at a certain voltage,and the oscillation disappears.At this point,the gas inside the tube is broken down and a large amount of ions and electrons are produced.The question arises:When did atomic ionization start? Is there only in the breakdown process,or as early as before the breakdown there? In this paper,the current of the gate G1 is measured by the current amplifier as a function of the voltage across the gate G2 in a tube with mercury,a gradual decrease in the current and a sudden reversal of the current were observed,this is a direct evidence of atomic ionization obtained for the first time.it shows that atomic ionization is a process of gradual development,before the gas breakdown there is ionization process,the number of atomic ionization increases with the acceleration voltage increases,the breakdown is the sudden amplification of ionization when the acceleration voltage increases to a certain extent.The extended significance of this finding is that since the existence of ionization,there are a variety of high excitation of the atom,Franck Hertz experimental curve is the result of a variety of excitation,and can not be considered only as a single level of excitation.%在弗兰克-赫兹实验中会观察到板极电流振荡曲线在某个电压下突然升高,振荡消失的现象,此时管子内部气体被击穿,产生大量离子和电子.由此产生一个疑问:原子电离是从何时开始的？是只存在于击穿过程中,还是早在击穿之前就存在了呢？通过电流放大器测量栅极G1的电流随栅极G2电压的变化曲线,观察到电流的逐步下降和突然反向的现象,获得了原子电离的直接证据,它说明:不仅在击穿时原子被电离,在击穿之前就存在着电离的过程,电离的数量随着加速电压增大而增多,击穿是电离增多到某种程度的突然放大.该发现的延伸意义是:既然有电离的存在,也就有各种高激发的存在,弗兰克-赫兹实验曲线是多种激发的综合结果,不能只考虑单一能级的激发.
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