Candidates for two-phonon octupole excitations in208Pb

Abstract

Following the identification of the lowest-spin member of the two-phonon octupole quartet in ${}^{208}\mathrm{Pb},$ the additional members of the multiplet have been sought with the ${(n,n}^{\ensuremath{'}}\ensuremath{\gamma})$ reaction. Based on energy arguments and $E1$ transition probabilities determined from Doppler-shift lifetime measurements, the 5286- and 5216-keV states are suggested as candidates for the ${2}^{+}$ and ${4}^{+}$ two-phonon octupole excitations in ${}^{208}\mathrm{Pb}.$ The difficulties of identifying the ${6}^{+}$ member of this quartet are examined.