Equilibrium Charges of Fission Fragments in Gases

A magnetic analysis method was used to measure the equilibrium charges of median-mass light and heavy fission fragments in ${\mathrm{H}}_2$, He, air, and A, and mass-97 fragments in He for wide ranges of fragment velocity and gas pressure. The data for the fragments in ${\mathrm{H}}_2$, air, and A showed pressure effects on the equilibrium charge which yield estimates of the mean radiative lifetime of excited ionized fragments which agree within 25%, in contrast with previous estimates differing by a factor of 10. An experimental test of the Bohr assumption, that the equilibrium charge of a heavy ion is equal to the number of electrons whose orbital velocities are lower than the translational velocity of the ion, showed the assumption to be only a rough approximation. Measurements of equilibrium charge as a function of atomic number of the stopping gas agree with previous measurements.