The spontaneous fission lifetime of 264 Fm has been studied within nuclear density functional theory by minimizing the collective action integral for fission in a two-dimensional quadrupole collective space representing elongation and triaxiality. The collective potential and inertia tensor are obtained self-consistently using the Skyrme energy density functional and density-dependent pairing interaction. The resulting spontaneous fission lifetimes are compared with the static result obtained with the minimum-energy pathway. We show that fission pathways strongly depend on assumptions underlying collective inertia. With the non-perturbative mass parameters, the dynamic fission pathway becomes strongly triaxial and it approaches the static fission valley. On the other hand, when the standard perturbative cranking inertia tensor is used, axial symmetry is restored along the path to fission; an effect that is an artifact of the approximation used. Introduction.-The spontaneous fission (SF) of a nucleus plays important role in many areas of science and applications [1][2][3]. In particular, it determines the stability of the heaviest and superheavy elements [4,5] and it impacts the formation of heavy elements at the final stages of the r-process through the recycling mechanism [6][7][8]. Therefore, a capability of theory to predict SF lifetimes in a reliable way is essential.The main ingredients for a theoretical determination of SF lifetimes are the collective potential and inertia tensor. For heavy systems, these quantities can be calculated by using the self-consistent mean field theory based on the energy density functional [9]. The potential energy surface (PES) is obtained by solving constrained HartreeFock-Bogoliubov equations (HFB) in a multidimensional space of collective coordinates. The collective inertia (or mass) tensor is obtained from the self-consistent densities by employing the adiabatic time-dependent HFB approximation (ATDHFB) [10][11][12]. Since SF is a quantummechanical tunneling process and the fission barriers are usually both high and wide, the SF lifetime is obtained semi-classically by minimizing the fission action integral in the collective space.The main objective of this work is to study SF by combining the microscopic density functional input with the sophisticated action minimization techniques. We demonstrate that the predicted SF pathway strongly depends on the choice of the collective inertia. In particular, in the commonly used perturbative cranking approximation, the variations of mass parameters due to level crossings (configuration changes) are underestimated; this re-

We formulate criteria for identification of the nuclear tetrahedral and octahedral symmetries and illustrate for the first time their possible realization in a Rare Earth nucleus 152 Sm. We use realistic nuclear mean-field theory calculations with the phenomenological macroscopic-microscopic method, the Gogny-Hartree-Fock-Bogoliubov approach and the general point-group theory considerations to guide the experimental identification method as illustrated on published experimental data. Following group-theory the examined symmetries imply the existence of exotic rotational bands on whose properties the spectroscopic identification criteria are based. These bands may contain simultaneously states of even and odd spins, of both parities and parity doublets at well defined spins. In the exact-symmetry limit those bands involve no E2-transitions. We show that coexistence of tetrahedral and octahedral deformations is essential when calculating the corresponding energy minima and surrounding barriers and that it has a characteristic impact on the rotational bands. The symmetries in question imply the existence of long-lived shape-isomers and, possibly, new waiting point nuclei -impacting the nucleosynthesis processes in astrophysics -and an existence of 16-fold degenerate particle-hole excitations. Specifically designed experiments which aim at strengthening the identification arguments are briefly discussed.

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Increasingly more intense beams of radioactive isotopes allow moving into unknown areas of the nuclear chart and exploring the limits in nuclear binding and proton-to-neutron ratio. New aspects of nuclear structure and important results for nuclear astrophysics are obtained. The paper provides some overview of experimental developments, facilities and research results; and is intended to set the stage for the many exciting examples of research presented in these proceedings.

Isospin mixing in the hot compound nucleus 80 Zr was studied by measuring and comparing the γ -ray emission from the fusion reactions 40 Ca + 40 Ca at E beam = 200 MeV and 37 Cl + 44 Ca at E beam = 153 MeV. The γ yield associated with the giant dipole resonance is found to be different in the two reactions because, in self-conjugate nuclei, the E1 selection rules forbid the decay between states with isospin I = 0. The degree of mixing is deduced from statistical-model analysis of the γ -ray spectrum emitted by the compound nucleus 80 Zr with the standard parameters deduced from the γ decay of the nucleus 81 Rb. The results are used to deduce the zero-temperature value, which is then compared with the latest predictions. The Coulomb spreading width is found to be independent of temperature.The issue of isospin impurity in nuclei has been a longstanding open problem in nuclear physics. In particular, its knowledge is interesting in connection with the properties of the isobaric analog states (IAS) and with the Fermi β decay of the N ≈ Z nuclei around the proton drip line. The evaluation of the isospin impurity provides an important correction to the Fermi-transition rates allowing the extraction, in a nucleusindependent way, of the up-down quark-mixing matrix element of the Cabibbo-Kobayashi-Maskawa matrix [1,2]. Concerning the IAS, they are known to have a narrow spreading width ↓ related to the isospin impurities [3,4] originating from the Coulomb interaction coupling them to states of different isospin.In general, the breaking of isospin symmetry can be observed using, as a magnifying lens, the decays which would be forbidden by the selection rules if isospin mixing was not to occur. This is the case of the neutron decay from the IAS [5] and of the E1 decay from self-conjugate nuclei [6].The giant dipole resonance (GDR), where the maximum strength of the E1 transitions is concentrated, is the ideal excitation mode where this selection rule of E1 decay can be fully exploited. This approach was employed to measure the E1 decay of the GDR in nuclei at a finite temperature produced with fusion-evaporation reactions [7][8][9][10][11]. Fusion-evaporation reactions allow the production of self-conjugate compound nuclei (CN) at high excitation energy which, in many cases, * Present address: CEA Saclay, F-91191 Gif-sur-Yvette, France. are far from the β-stability valley. The use of a self-conjugate projectile and target ensures that the CN produced in fusion reactions has isospin I = 0. Therefore, E1 emission associated with the decay of the GDR is hindered due to the fact that, if the isospin of the initial state is pure, only the less-numerous I = 1 final states can be reached in the decay [12]. Conversely, if the initial state is not pure in isospin but contains an admixture of I = 1 states, it can decay to the more numerous I = 0 final states. Thus, the first-step γ yield depends on the degree of isospin mixing of the CN. In addition, at a finite temperature one expects a partial restoration of the isospin symmetry b...

The review covers recent developments and achievements in the dynamical description of fission process at high excitation energy. It is shown that the dynamical approach based on multidimensional Langevin equations combined with the statistical description of nuclear decay by particles evaporation is capable of fairly well describing the formation of fission fragment mass-energy, charge, and angular distributions of fission fragments in coincidence with the pre-and post-scission particle emission. The final yields of fission and evaporation residues channels products could be obtained. The detailed description of fission dynamics allows studying different stages of fission process, indicating the most important ingredients governing fission process and studying in detail such fundamental nuclear properties as nuclear viscosity and fission timescale. The tasks and perspectives of multidimensional dynamical approach are also discussed.

The properties of pygmy dipole states in 208Pb were investigated using the 208Pb(17O, 17O'γ) reaction at 340 MeV and measuring the γ decay with high resolution with the AGATA demonstrator array. Cross sections and angular distributions of the emitted γ rays and of the scattered particles were measured. The results are compared with (γ, γ') and (p, p') data. The data analysis with the distorted wave Born approximation approach gives a good description of the elastic scattering and of the inelastic excitation of the 2+ and 3- states. For the dipole transitions a form factor obtained by folding a microscopically calculated transition density was used for the first time. This has allowed us to extract the isoscalar component of the 1- excited states from 4 to 8 MeV.

K. HADYŃSKA-KLȨK et al. PHYSICAL REVIEW C 97, 024326 (2018) A Coulomb-excitation experiment to study electromagnetic properties of 42 Ca was performed using a 170-MeV calcium beam from the TANDEM XPU facility at INFN Laboratori Nazionali di Legnaro. γ rays from excited states in 42 Ca were measured with the AGATA spectrometer. The magnitudes and relative signs of ten E2matrix elements coupling six low-lying states in 42 Ca, including the diagonal E2 matrix elements of 2 + 1 and 2 + 2 states, were determined using the least-squares code GOSIA. The obtained set of reduced E2 matrix elements was analyzed using the quadrupole sum rule method and yielded overall quadrupole deformation for 0 + 1,2 and 2 + 1,2 states, as well as triaxiality for 0 + 1,2 states, establishing the coexistence of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in 42 Ca. The experimental results were compared with the state-of-the-art large-scale shell-model and beyond-mean-field calculations, which reproduce well the general picture of shape coexistence in 42 Ca.