Simultaneous Measurement of beta- Decay to Bound and Continuum Electron States

We report the first measurement of a ratio {lambda}{sub {beta}{sub b}}/{lambda}{sub {beta}{sub c}} of bound-state ({lambda}{sub {beta}{sub b}}) and continuum-state ({lambda}{sub {beta}{sub c}}) {beta}{sup -}-decay rates for the case of bare {sup 207}Tl{sup 81+} ions. These ions were produced at the GSI fragment separator FRS by projectile fragmentation of a {sup 208}Pb beam. After in-flight separation with the B{rho}-{delta}E-B{rho} method, they were injected into the experimental storage-ring ESR at an energy of 400.5A MeV, stored, and electron cooled. The number of both the {sup 207}Tl{sup 81+} ions and their bound-state {beta}{sup -}-decay daughters, hydrogenlike {sup 207}Pb{sup 81+} ions, were measured as a function of storage time by recording their Schottky-noise intensities. The experimental result, {lambda}{sub {beta}{sub b}}/{lambda}{sub {beta}{sub c}}=0.188(18), is in very good agreement with the value of 0.171(1) obtained from theory employing spectra of allowed transitions.