The new neutron-rich nuclei231Fr and231Ra
The new neutron-rich isotope231Fr has been produced in a spallation reaction of238U induced by 600 MeV protons and identified by mass-separation and decay spectroscopy. In addition, the so far unknown231Ra and the known231Ac have been observed as daughter products. The Z-assignments were performed via the decay of KX-rays, and genetic relationships. Half-lives of 17.5(8) s and 103(3) s were obtained for231Fr and231Ra, respectively.