Nuclear pears: Recent developments and future prospects

We report studies of examples of reflection-asymmetric nuclei which are difficult to access using compound nucleus reactions. The octupole radium isotopes with N > 132 and radon isotopes are not accessible by reactions employing stable targets and beams; we have shown that multinucleon transfer reactions can populate these nuclei with sufficient yield for their structure to be determined. We report high-spin studies in Rn-218,Rn-220,Rn-222 and Ra-222,Ra-224,Ra-226,Ra-228,Ra-230: these show that the Ra isotopes with A < 228 have the characteristics of octupole deformed nuclei whereas the Rn isotopes behave like octupole vibrators. Measurements of the B(E1)/B(E2) ratios indicate that the electric dipole moment in these nuclei is constant with spin. The most octupole deformed nuclei are predicted to be uranium isotopes with N approximate to 132; measurements of the very fissile nucleus U-226 suggest that it is octupole deformed and has a large intrinsic electric dipole moment. Finally, we speculate that the best examples of pear shapes are the hyperdeformed minima predicted to lie low in uranium isotopes with N approximate to 140; their signature of high-multiplicity low-energy El photon cascades should be detectable using present-day high-efficiency germanium arrays.