. Radioactive transformations . connections acquire a positive charge. The rate atwhich the plate B rises in potential is a relative measure of thecurrent through the gas. When V has a small value, the cur-rent is small, but gradually increases with rise of V, until astage is reached where the current increases very slightly fora large increment of the value of V. The relation between the 26 RADIOACTIVE TRANSFORMATIONS current and the applied voltage is seen in Fig. 4. The shapeof this curve receives a simple explanation on the ionizationtheory. The ions move with a velocity proportional to th
. Radioactive transformations . connections acquire a positive charge. The rate atwhich the plate B rises in potential is a relative measure of thecurrent through the gas. When V has a small value, the cur-rent is small, but gradually increases with rise of V, until astage is reached where the current increases very slightly fora large increment of the value of V. The relation between the 26 RADIOACTIVE TRANSFORMATIONS current and the applied voltage is seen in Fig. 4. The shapeof this curve receives a simple explanation on the ionizationtheory. The ions move with a velocity proportional to thestrength of the electric field. In a weak field there is thusa slow movement of the positive and negative ions past oneanother. A large proportion of the ions have time to recom-bine before they reach the electrodes, and the current observedthrough the gas is consequently small. As the voltage in-creases, the velocity of the ions increases, and there is less timefor recombination. Finally, in a strong field practically all the. VOLTS. Fig. saturation curve for an ionized gas. ions are swept to the electrodes before any appreciable recom-bination can occur. The maximum or saturation currentthrough the gas is then a measure of the charge carried by theions produced per second by the radiation, i. e., it is a measureof the total rate of production of ions. The term saturation, which was applied initially from theresemblance of the current-voltage curve to the magnetizationcurve for iron, is not very suitable, but has come into use as aconvenient though inaccurate method of expressing an experi-mental fact. Other conditions being the same, the voltage required toproduce saturation increases with the intensity of the ioniza- HISTORICAL INTRODUCTION 27 tion, i. c, with increase in activity of the substance under ex-amination. Increase of the distance between the plates lowersthe value of the electric field and increases the distance overwhich the ions move. Both of these c
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