New isotope227Rn and revised halflives for223Rn and226Rn

Neutron-rich isotopes of radon, produced by spallation reactions in a ThC2 target and selected chemically, were mass-separated and used as samples for radiation counting experiments. Assignments of the activities to radon isotopes were confirmed by genetic relationships to the previously known francium daughters. The halflife for the new isotope227Rn is 23±1 s and that for226Rn is 7.4±0.1 min. X-rays,γ-rays, and conversion electrons from the223Rn activity were measured. The decay patterns ofK X-rays and known gamma transitions in the223Fr daughter yield a halflife of 23.2± 0.4 min for223Rn, in contrast to the value of 43± 5 min reported earlier. Energies, intensities, and likely multipolarities for the most prominent gamma transitions in the223Rn→223Fr decay are presented.