Four new neutron-rich, fission-product nuclei have been identified at the on-line mass separator TRISTAN at Brookhaven National Laboratory. Their half-lives have been measured to be, for ${}_{}{}^{156}{}_{}{}^{}\mathrm{Pm}$, $T_{\frac{1}{2}}=28.2\mathrm{}\pm 1.1$ sec; for ${}_{}{}^{159}{}_{}{}^{}\mathrm{Sm}$, $T_{\frac{1}{2}}=15\mathrm{}\pm 2$ sec; for ${}_{}{}^{160}{}_{}{}^{}\mathrm{Sm}$, $T_{\frac{1}{2}}=8.7\mathrm{}\pm 1.4$ sec; and for ${}_{}{}^{161}{}_{}{}^{}\mathrm{Eu}$, $T_{\frac{1}{2}}=27\mathrm{}\pm 3$ sec. These nuclei are of particular importance in nucleosynthesis calculations, since they lie in the region of the rare-earth maximum in $r$ process abundances. A comparison of these and other new half-lives with recent calculations discloses a characteristic pattern of discrepancies.

• Received 20 November 1985

DOI:https://doi.org/10.1103/PhysRevLett.56.1547