V. The velocity of the ions produced in gases by Röntgen rays

Abstract

The electrical conductivity which is imparted to gases by their exposure to Röntgen rays has been explained by J. J. Thomson and E. Rutherford on the hypothesis of a formation of oppositely charged carriers throughout the volume of the gas. The motion of these carriers or ions when in an electric field constitutes the observed conductivity, and the recovery of the insulating property of a gas after an exposure to the rays is due partly to the recombination of the oppositely charged ions and partly to their impact with the boundaries. An estimate of the sum of the velocities with which the positive and negative ions move in air when in a unit electric field was first obtained by J. J. Thomson and E. Rutherford, and later E. Rutherford, by the same indirect method, determined the sum of the velocities of the ions in a number of gases. This method involved the determination of the rate of recombination of the ions, the saturation current obtained through the gas by the use of a strong electric field, and the current obtained with some small non-saturating electric force. E. Rutherford also describes an experiment in which the velocities of the two ions in air were obtained separately by a direct method, and found to be approximately equal. The writer has since shown that in general the two velocities are not equal, and for those gases for which the ratio of the two velocities was determined the negative ion moved the faster in nearly all cases.