J. C. Bacelar

Bio: J. C. Bacelar is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Moment of inertia & Nuclear reaction. The author has an hindex of 12, co-authored 15 publications receiving 304 citations.

Slow and fast high-spin sequences in 158Er.

Abstract: LBL-19598 Slow and Fast High-Spin Sequences in 158Er P.O. Tjom,+ R.M. Diamond, J.C. Bacelar, E.M. Beck, M.A. Deleplanque, J.E. Draper,+ and F.S. Stephens Nuclear Science Division Lawrence Berkeley Laboratory University of California Berkeley, California 94720 Two branches are observed feeding the 38+ level of the yrast line in 158Er. Two -i.2 MeV cascade transitions constitute a fast(< 1 ps) collective component, probably with only minor changes in shape and structure from those at lower spin. Four slower y rays (> 2 ps) suggest a transition to a different shape and structure, most likely to an oblate 46+ state with all valence particles maximally aligned, a band termination. This work was supported by the Director, Office of Energy Research, Division ~ of Nuclear Physics of the Office of High Energy and Nuclear Physics of the U.S. Department of Energy under Contract DE-AC03-76SF00098. + On leave from the Institute of Physics, University of Oslo, Norway +university of California, Davis

Lifetime measurements of high-spin states in 166Yb.

Abstract: The Doppler-shift attenuation method was used to measure lifetimes of yrast states in $^{166}\mathrm{Yb}$. Values of $\ensuremath{\tau}$ range from 0.16(2) ps at ${24}^{+}$. to 0.05(1) ps at ${34}^{+}$. The $B(E2)$ values decrease from 240 to 120 single-particle units in this spin range, indicating a loss of collectivity which likely reflects a change of the nucleus towards triaxial shape. The side-feeding times are consistent with rotational cascades having moments of inertia 25% larger than the yrast sequence or $B(E2)$ values around 60 single-particle units.

Spontaneous symmetry breaking in rotating nuclei

Abstract: The concept of spontaneous symmetry breaking is applied to the rotating mean field of nuclei. The description is based on the tilted-axis cranking model, which takes into account that the rotational axis can take any orientation with respect to the deformed density distribution. The appearance of rotational bands in nuclei is analyzed, focusing on weakly deformed nuclei at high angular momentum. The quantization of the angular momentum of the valence nucleons leads to new phenomena. Magnetic rotation represents the quantized rotation of the anisotropic current distribution in a near spherical nucleus. The restricted amount of angular momentum of the valence particles causes band termination. The discrete symmetries of the mean-field Hamiltonian provide a classification scheme of rotational bands. New symmetries result from the combination of the spatial symmetries of the density distribution with the vector of the angular momentum. The author discusses in detail which symmetries appear for a reflection-symmetric density distribution and how they show up in the properties of the rotational bands. In particular, the consequences of rotation about a nonprincipal axis and of breaking the chiral symmetry are analyzed. Also discussed are which symmetries and band structures appear for non-reflection-symmetric mean fields. The consequences of breaking the symmetry with respect to gauge and isospin rotations are sketched. Some analogies outside nuclear physics are mentioned. The application of symmetry-restoring methods to states with large angular momentum is reviewed.