Phase Transitions and Shape Coexistence in Atomic Nuclei
- PDF / 949,322 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 76 Downloads / 181 Views
CLEI Theory
Phase Transitions and Shape Coexistence in Atomic Nuclei R. V. Jolos1), 2)* , E. A. Kolganova 1), 2) , L. A. Malov1), E. V. Mardyban1), 2) , D. A. Sazonov2) , and T. M. Shneidman1), 3) Received December 25, 2019; revised December 25, 2019; accepted December 25, 2019
Abstract—Examples of phase transitions occurring in atomic nuclei in response to an increase in the excitation energy and angular momenta and in response to a change in the number of nucleons are considered. The possibility of describing such transitions within collective models based on a Hamiltonian that depends on a relatively small number of dynamical variables is demonstrated. DOI: 10.1134/S1063778820040092
1. INTRODUCTION
in response to a change in the number of nucleons. These are transitions from a higher to a lower Heavy atomic nuclei are systems that involve an symmetry of the nuclear shape but, of course, are enormous number of degrees of freedom. At relatively not phase transitions well known in thermodynamics low energies, however, their properties may be deand caused by a change in temperature and pressure. scribed in terms of a Hamiltonian that depends on a Because of a finite number of nucleons in nuclei, these relatively small number of dynamical variables. For transitions from one nuclear shape to another are example, a quadrupole mode is among the most im- smeared, even though sharp changes in the nuclear portant dynamical variables that determine the prop- shape are observed upon an insignificant change in erties of nuclei. Of course, the equations relating the number of nucleons. these five quadrupole degrees of freedom to the coorIn considering stable nuclei, not only were phase dinates that describe the motion of individual nucleons are very complicated, but, within a phenomeno- transitions observed upon a change in the number logical treatment, the Hamiltonian involves only dy- of nucleons, but they were also caused by a change namical variables. Such a Hamiltonian describes in the angular momentum of a nucleus. In recent those excited states of nuclei that are associated with years, the interest of nuclear physicists shifted toward quadrupole shape vibrations with respect to the equi- studying nuclei lying far from the stability region. librium shape and the effect of these states on the These are nuclei in which states corresponding to drastically different nuclear shapes were found to exist motion of nucleons. Collective variables underlie the concept of an at different excitation energies. This led to formulatequilibrium shape of atomic nuclei—first of all, the ing the concept of shape coexistence. ground-state equilibrium shape of the nucleus. SpecifA self-consistent field formed as the result of conically, the concepts of spherical and deformed nuclei, sistent motion of a large number of intranuclear nuas well as of nuclei of transitional shape intermediate cleons is a basic feature of atomic nuclei that distinbetween the spherical and deformed shapes, arose guishes them from many other microscopic systems. within col
Data Loading...
