Identification of new neutron-rich rare-earth isotopes produced in 252Cf fission.

New neutron-rich isotopes of several rare-earth elements have been identified using on-line mass separation. The observed decay rates of K x rays in the mass separated fractions for which 153less than or equal toAless than or equal to162, together with the associated ..gamma..-decay spectra, provided direct isotopic identifications. New isotopes observed, with values of their half lives given in parentheses, are /sup 153/Pr (4.3 +- 0.2 s), /sup 155/Nd (8.9 +- 0.2 s), /sup 156/Nd (5.47 +- 0.11 s), /sup 157/Pm (10.90 +- 0.20 s), /sup 158/Pm (4.8 +- 0.5 s), and /sup 162/Eu (10.6 +- 1.0 s). In addition, we have confirmed recent reports of the observation of /sup 153/Nd (28.9 +- 0.4 s), /sup 154/Nd (25.9 +- 0.2 s), /sup 156/Pm (26.70 +- 0.10 s), /sup 159/Sm (11.37 +- 0.15 s), and /sup 160/Sm (9.6 +- 0.3 s). These half-life values are compared to the reuslts of theoretical predictions.