[en] Recently, the idea of quantum phase transitions has been applied to equilibrium shape changes in finite atomic nuclei. An introduction to and discussion of this concept, both from the macroscopic perspective and from a microscopic approach, in terms of shell structure and residual interactions is presented. Following this, the quantitative predictions of the critical point symmetries (CPS) X(5) and E(5) are discussed in some detail and compared to the data in a number of nuclei and mass regions. Any successful new model paradigm soon generates modifications to improve the predictions and, likewise, often spawns related models inspired by the original ansatz. This is eminently true of the CPS and we make an effort to briefly discuss this rapidly advancing area in terms of a number of recent modifications to the CPS as well as related models that are couched in a geometrical perspective. (topical review)

[en] Constant contours of basic observables are discussed in the context of the interacting boson approximation (IBA) symmetry triangle. Contours that exhibit orthogonal crossing within the triangle are presented as a method for determining a set of parameter values for a particular nucleus and trajectories for isotopic chains. A set of contours that highlights a class of nuclei that are outside the two-parameter IBA-1 Hamitonian space is also presented

[en] A common interpretation of the light Pt isotopes involves the coexistence and mixing with proton intruder states from above the Z = 82 shell gap. An alternative description of the Pt isotopes using a simple, single configuration, the two-parameter interacting boson approximation model Hamiltonian, is discussed. To test these predictions, experiments on ¹⁹²Pt were performed. New coincidence data found no support for several low-energy, low-spin states previously proposed in β decay. Results from an (α, 2n) experiment identified states of the γ band up to spin 9⁺. Results of these experiments are discussed in terms of IBA calculations

[en] Recent theoretical and experimental work focusing on nuclei in spherical-deformed transition regions has sparked considerable interest in phase transitional nuclei. A review of searches and experimental results on critical point nuclei in the A = 130 and A = 150 regions is presented

[en] The US Nuclear Data Program is charged with collecting, analyzing and archiving information critical to basic nuclear research and to the development of nuclear technologies. Users of nuclear data require detailed uncertainty information for a variety of reasons. In this paper, we review some of the main aspects of the generation and use of uncertainty information, linking to structure, astrophysics, and reaction data. (paper)

[en] Here, we calculate the Inverse Beta Decay (IBD) antineutrino spectrum generated by nuclear reactors using the summation method to understand deviations from the smooth Huber-Mueller model due to the decay of individual fission products, showing that plotting the ratio of two adjacent spectra points can effectively reveal these deviations. We obtain that for binning energies of 0.1 MeV or lower, abrupt changes in the spectra due to the jagged nature of the individual antineutrino spectra could be observed for highly precise experiments. Surprisingly, our calculations also reveal a peak-like feature in the adjacent points ratio plot at 4.5 MeV even with a 0.25 MeV binning interval, which we find is present in the IBD spectrum published by Daya Bay in 2016. We show that this 4.5 MeV feature is caused by the contributions of just four fission products, ⁹⁵Y, ^98,101Nb and ¹⁰²T_c. This would be the first evidence of the decay of a few fission products in the IBD antineutrino spectrum from a nuclear reactor. This result is supported by applying the same numerical technique to measured aggregate electron spectra.

[en] A simple, empirical, easy-to-measure effective order parameter of a first-order phase transition in atomic nuclei is presented, namely, the ratio of the energies of the first excited 6⁺ and 0⁺ states, distinguishing between first- and second-order transitions, and taking on a special value in the critical region, as data in Nd-Dy show. In the large N_B limit of the interacting boson approximation model, a repeating degeneracy between alternate yrast and successive 0⁺ states is found in the critical region around the line of a first-order phase transition, pointing to a possible underlying symmetry

[en] We investigate the effects of β-γ mixing using branching ratios between the 2_γ⁺ level and the ground state band in well-deformed nuclei. We find that the deviations from the well-known Alaga rules vary as a function of the energy separation between the 2_γ⁺ and 2_β⁺ levels. For nuclei where these two intrinsic excitations are nearly degenerate, we find two classes of behavior. For one of those, the systematics can be reproduced in a simple bandmixing formalism but only with an anomalously strong interaction strength between the 2_γ⁺ and 2_β⁺ levels, on the order of tens of keV. This result is supported by X(E0/E2;2_γ⁺→2₁⁺) values that are large for these nuclei (where measured), indicating significant K=0 components in the 2_γ⁺ levels. In the other class, there is virtually no mixing. These nuclei have previously been associated with near-SU(3) structure

[en] Low-lying collective excited states of ¹⁹⁴Pt have been studied via the ¹²C(¹⁹⁴Pt,¹⁹⁴Pt^*) projectile Coulomb excitation reaction at 85% of the Coulomb barrier (850 MeV) using the Gammasphere Ge-detector array at Argonne National Laboratory. Absolute E2 transition strengths have been obtained from the Coulex cross sections that were deduced from the relative γ-ray yields. They are discussed with respect to the structure suggested by the O(6) symmetry of the Interacting Boson Model.

[en] The first example of an empirically manifested quasidynamical symmetry trajectory in the interior of the symmetry triangle of the interacting boson approximation model is identified for large boson numbers. Along this curve, extending from SU(3) to near the critical line of the first order phase transition, spectra exhibit nearly the same degeneracies that characterize the low energy levels of SU(3). This trajectory also lies close to the Alhassid-Whelan arc of regularity, the unique interior region of regular behavior connecting the SU(3) and U(5) vertices, thus offering a possible symmetry-based interpretation of that narrow zone of regularity amidst regions of more chaotic spectra.