Multiple Valency in the Ionization by Alpha Rays

Valency of Ions Produced by $\alpha$-rays.—The well-known Millikan oil-drop method, in which the valency of individual ions caught on the droplet immediately after they are produced is determined by the change of speed of the droplet due to each, was used with slight modifications which simplified the procedure. In air, out of 350 positive ions produced by x-rays at the end of their range, only 3 per cent, could have been doubly charged and most if not all of these were probably not doubles but two successive singles. In helium, an extensive series of 2,150 positive catches were observed with gradually increasing pressure to determine not only whether doubles were produced but also the variation of the number of doubles with the range. It was found that an appreciable proportion of real doubles is produced when the ranges of the rays are equivalent to between 4 and 30 mm. of helium at atmospheric pressure, the maximum proportion being about 10 per cent., for the range of maximum ionizing power. That this result was real was proved by the fact that when hydrogen was substituted, even for the range of maximum ionization, the proportion of apparent doubles was only 5 out of 200 positive ions. The previously reported negative result for mercury dimethyl was confirmed.