[en] Most of the important advances in the description of collective nuclear phenomena have been based upon the assumption of a reflection symmetry relative to a plane perpendicular to the symmetry axis of the nucleus. It is known, however, that reflection asymmetric shapes, such as alpha clustering configurations and dynamic octupole deformations, can be found in many regions of the periodic table. Isotopes of Ra and Th have long been known to exhibit characteristics suggesting the possibility that static intrinsic reflection asymmetric shapes are present. We examine the nature of reflection asymmetry in Ra and Th by first studying, in detail, three nuclei, ²¹⁶Rn, ²¹⁹Ra and ²²⁰Ra, produced in the ¹⁴C + ²⁰⁸Pb fusion reaction using several techniques of gamma ray spectroscopy. Level spectra have been constructed for these nuclei to excitation energies of 2.1 MeV, 4.9 MeV and 3.6 MeV, respectively. Second, we discuss our results within the context of the systematic behavior of other Rn, Ra and Th isotopes and its relationship to predictions of alpha particle cluster, octupole vibration and static octupole deformation models. Third, we find that several observables seen in the Ra-Th region are qualitatively similar to those found in the Sm-Gd region. Finally, we see that the excitation spectra observed in the mass 217 and 219 Ac and Ra isotopes are described quite well in terms of a weak particle-core coupling model which is generally successful for weakly deformed nuclei

[en] The orderly systematic behavior of low energy octupole states, which in spherical and weakly deformed nuclei are 3₁^- states, makes anomalies in octupole behavior readily identifiable. Such anomalies point to interesting nuclear structure effects, including rapidly changing shell structure and interactions between stable nuclear shapes and octupole phonons. Parameters for analysis of octupole behavior, fragmentation of the low energy octupole state, several examples of novel octupole behavior, and the location of candidates for static ocutpole deformation are discussed. In addition, a number of experiments which might illuminate the nuclear structure questions raised here are suggested

[en] In many even-even nuclei, bands of negative parity states have been interpreted as open-quotes octupole bandsclose quotes, which are sequences of vibrational or rotational excitations coupled to a low energy octupole phonon. Careful experimental examination of these structures is of interest because octupole phonons are generally considered to be unstable at high angular momentum. Results from experimental studies of octupole band structures in three nuclei are presented. Two of these nuclei, ^144,146Nd, have been studied via inelastic scattering of 35 MeV protons. The third nucleus, ⁷⁴Se, has been examined using the techniques of high spin gamma-ray spectroscopy

[en] It is demonstrated that recent experimental results on high spin states of ^128,129Ba offer substantial new evidence for static octupole deformation in these nuclei. (orig.)

[en] The fragmentation of the low energy octupole state in ^196,198Pt appears to be anomalously large. The (n,n'γ) reaction has been used in an effort to make farm spin and parity assignments for possible 3^- states which occur at high energies in ¹⁹⁶Pt and to confirm the fragmentation. The fragmentation can be explained in the context of the Interacting Boson Approximation in terms of the O(6) nature of ^196,198Pt and can be simply understood in terms of the d-boson structure of the ground and 3^- states

[en] The systematic behavior of 3₁^- states is used to identify N and Z values at which maximum octupole collectivity occurs. The results are used to suggest nuclei in which static octupole deformation might appear

[en] It is suggested that ^126,128Ba achieve static octupole deformation at angular momenta of 11ℎ, and that ⁷⁸Kr is evolving toward octupole deformation at the highest angular momenta observed. These nuclei require higher angular frequencies to stabilize octupole deformation than those nuclei previously found to be octupole deformed in the A=145 and 222 mass regions because of their relative stiffness to octupole vibrations in their ground states

[en] Electric dipole moments are extracted from data for E1 transitions deexciting octupole vibration states in nineteen nuclei. The moments are then compared to values calculated using the droplet model prescription of Dorso, Myers, and Swiatecki. It is found that the E1 moments in quadrupole deformed nuclei can be reproduced with the droplet model using the same model parameters that reproduce atomic masses and fission barriers. This result supports the suggestion of Butler and Nazarewicz that single particle effects are usually much smaller than macroscopic effects in E1 transitions associated with octupole vibrations in reflection symmetric deformed nuclei

[en] It is shown that the energy shift of the πh_11/2 orbit near N=90, which results in the collapse of the Z=64 subshell gap, affects the behavior of low-energy octupole states in the vicinity of Gd

[en] Strong E1 transitions of greater than 10^-3 Weisskopf units occur in many octupole states in the deformed rare earth region. It is shown using the droplet model that the electric dipole moment resulting from the macroscopic behaviour of the octupole phonon cannot by itself account for the observed E1 strengths, and it is observed that this result is consistent with the proposal of Donner and Greiner and of Zilges von Brentano and Richter that admixtures of the giant dipole resonance into the low energy octupole states are responsible for the fast E1 transitions. It is also suggested that calculations similar to those performed by Egido and Robledo for N ≤ 92 nuclei may be able to reproduce E1 transitions in N = 94-104 nuclei. (orig.)