Time-lag τ
l of light emission relative to the initiation of electric current flow in various flash tubes is studied experimentally. The light emission is picked up by a vacuum photocell and is recorded by an oscilloscope.
The influence of applied voltage on τ
l is similar, in general trend, to the voltage dependency on the formative time-lag of electric current which was already reported in the author's previous paper, namely, τ
l decreases with increasing voltage.
Regarding the dependency of τ
l on the nature of gas in the flash tube, if all the other condi-tions such as discharge voltage, capacity and gas pressure are the same, τ
l in Xe is the largest (1_??_10μ sec), decreasing in sequence of Ar, Ne, He. The same relation holds for the dependency of intensity of emitted light on the nature of gas. The formative time-lags of discharge current and peak current, however, are affected by the nature of gas in reversed sequence.
An attempt is made to explain the mechanism of the time-lag of light emission. The con-tinuous spectrum seen in a discharge of this kind in rare gases originates from the dissociation of diatomic molecular ions which comprise metastable atoms, and, for that reason, the observed time-lag can be explained as consisted of two stages: first, the time interval necessary for the electron temperature to rise and effect a sufficient number of metastable atoms to be formed: second, the time interval in which molecular ions are formed by collision between the metastable atoms and neutral atoms, the collision being caused by the subsequent rise of ion moleculer temperature.
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