## Abstract

The distributions of charges carried by fast nitrogen, oxygen and fluorine ions after passing through a thin organic film have been investigated by magnetic analysis. The ions, which were accelerated in the Birmingham cyclotron, had velocities between 0$\cdot $86 and 1$\cdot $43 $\times $ 10$^{9}$ cm s$^{-1}$, corresponding to kinetic energies in the range 6$\cdot $2 to 20$\cdot $4 MeV, and carried average charges between 4$\cdot $86 and 6$\cdot $63 positive electron units after emerging from the film. The dependence of the ionic charge on the velocity and on the atomic number of an ion passing through matter is found to be in good qualitative agreement with the criterion of Lamb. This states that the velocity of the ion must be such that $\frac{1}{2}$mv$^{2}\gtrsim $ I, where m is the electron mass and v the velocity of the ion, if an electron of binding energy I is to be removed from the ion. For any of the ions used, not more than two or three charge states were found to occur with large probability at a given velocity, indicating a strong variation with ionic charge of the cross-sections for electron capture and for electron loss by the ion. The average charges carried by the ions are compared with the statistical theory of Brunings, Knipp & Teller (1941).