Quadrupole moments in the lead isotopes

Abstract

The static quadrupole moments QJπ and reduced excitation probabilities (BEλ) of the first excited states of the nuclei ²⁰⁴Pb, ²⁰⁸Pb, and ²⁰⁸Pb have been determined using the reorientation effect in Coulomb excitation. The Coulomb excitation probabilities were measured by resolving inelastically and elastically backward-scattered ⁴He, ¹²C, and ¹⁶O projectiles in an annular surface barrier detector. In the case of 204Pb and ²⁰⁸Pb, safe bombarding energies were determined for all projectiles. In the case of ²⁰⁸Pb, safe bombarding energies were measured for 180, but were assumed for ⁴He. The small values obtained for Q₂+ indicate that ²⁰⁴Pb is only weakly deformed, and that ²⁰⁶Pb approaches sphericity. The measured value of Q₃_ for ²⁰⁸Pb is much smaller in magnitude than those obtained in previous measurements, and is consistent with most theoretical predictions.