Seminarium Fizyki Jądra Atomowego
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2022-04-21 (10:15) 
prof. José Enrique García-Ramos (Facultad de Ciencias Experimentales, Universidad de Huelva, Spain)
On the nature of the shape coexistence and the quantum phase transition phenomena in the zirconium and lead region
The shape coexistence phenomenon is related with the presence in the same energy region of eigenstates with different deformations. The lead region is considered as a paradigm for shape coexistence and several decades of experimental effort have supported this believe. In particular, long chains of the Pb, Hg, Pt and Po isotopes have been measured and a rich experimental body of data concerning, excitation energies, electromagnetic transition rates, radii, magnetic g-factors, alpha-hindrance factors and Coulomb excitation reactions, has been obtained.
In the case of Pb and Hg, the presence of intruder states is self-evident inspecting the parabolic energy systematics of the intruder states. However, in the case of Pt and Po, the presence and influence of intruder states is not obvious.
On the other hand, the concept of quantum phase transition (QPT), which has gained a lot of attention in nuclear physics, among other fields, during the last twenty years, appears when the Hamiltonian that describes the quantum system can be written in terms of two pieces, at least, each one with a given symmetry, and a Hamiltonian parameter, i.e., a control parameter, allows to pass from one to the other symmetry. This passing supposes a sudden change in a control parameter and a discontinuity in the ground-state energy or in some of its derivatives.
The rare-earth region around N=90 is very well known for containing examples of QPT's, in particular, the even-even isotope chains of Nd, Sm, or Gd show first order QPTs. In other regions, as in Ba or Ru even-even isotope chains, second order QPTs appear.
The goal of this seminar is to try to clarify the connection between shape coexistence and QPT, two seemingly unrelated phenomena, but that, once studied in deep, share common aspects: the rapid change in the ground state structure when going through an isotope chain or the presence in the mean-field energy surface of several minima. To illustrate the similarities and differences between both phenomena, we will focus on the Zr and Sr region which is known for the rapid change of the ground state deformation and also for the presence of intruder states coming from two-particle two-hole excitations across Z=40 shell closure. We will also pay attention to the lead region.
[1] J.E. Garcia-Ramos, K. Heyde, "The Pt isotopes: Comparing the Interacting Boson Model with configuration mixing and the extended consistent-Q formalism", Nuclear Physics A 825, 39-70 (2009).
[2] J.E. Garcia-Ramos, K. Heyde, "Nuclear shape coexistence: A study of the even-even Hg isotopes using the interacting boson model with configuration mixing", Physical Review C, 89, 014306-24pp (2014).
[3] J.E. Garcia-Ramos, K. Heyde, "Quest of shape coexistence in Zr isotopes", Physical Review C 100, 044315-25p (2019).
[4] J.E. Garcia-Ramos, K. Heyde, "Subtle connection between shape coexistence and quantum phase transition: The Zr case", Physical Review C 102, 054333-16p (2020).
[5] E. Maya-Barbecho and J.E. Garcia-Ramos, "Shape coexistence in Sr isotopes", Physical Review C (in press).
Seminarium odbędzie się zdalnie na zoom-ie. Link jest dostępny od 10.00:
https://us02web.zoom.us/j/81630676206?pwd=TGhheWUwR3lLOFdtd0NFZW1VdnMyZz09
In the case of Pb and Hg, the presence of intruder states is self-evident inspecting the parabolic energy systematics of the intruder states. However, in the case of Pt and Po, the presence and influence of intruder states is not obvious.
On the other hand, the concept of quantum phase transition (QPT), which has gained a lot of attention in nuclear physics, among other fields, during the last twenty years, appears when the Hamiltonian that describes the quantum system can be written in terms of two pieces, at least, each one with a given symmetry, and a Hamiltonian parameter, i.e., a control parameter, allows to pass from one to the other symmetry. This passing supposes a sudden change in a control parameter and a discontinuity in the ground-state energy or in some of its derivatives.
The rare-earth region around N=90 is very well known for containing examples of QPT's, in particular, the even-even isotope chains of Nd, Sm, or Gd show first order QPTs. In other regions, as in Ba or Ru even-even isotope chains, second order QPTs appear.
The goal of this seminar is to try to clarify the connection between shape coexistence and QPT, two seemingly unrelated phenomena, but that, once studied in deep, share common aspects: the rapid change in the ground state structure when going through an isotope chain or the presence in the mean-field energy surface of several minima. To illustrate the similarities and differences between both phenomena, we will focus on the Zr and Sr region which is known for the rapid change of the ground state deformation and also for the presence of intruder states coming from two-particle two-hole excitations across Z=40 shell closure. We will also pay attention to the lead region.
[1] J.E. Garcia-Ramos, K. Heyde, "The Pt isotopes: Comparing the Interacting Boson Model with configuration mixing and the extended consistent-Q formalism", Nuclear Physics A 825, 39-70 (2009).
[2] J.E. Garcia-Ramos, K. Heyde, "Nuclear shape coexistence: A study of the even-even Hg isotopes using the interacting boson model with configuration mixing", Physical Review C, 89, 014306-24pp (2014).
[3] J.E. Garcia-Ramos, K. Heyde, "Quest of shape coexistence in Zr isotopes", Physical Review C 100, 044315-25p (2019).
[4] J.E. Garcia-Ramos, K. Heyde, "Subtle connection between shape coexistence and quantum phase transition: The Zr case", Physical Review C 102, 054333-16p (2020).
[5] E. Maya-Barbecho and J.E. Garcia-Ramos, "Shape coexistence in Sr isotopes", Physical Review C (in press).
Seminarium odbędzie się zdalnie na zoom-ie. Link jest dostępny od 10.00:
https://us02web.zoom.us/j/81630676206?pwd=TGhheWUwR3lLOFdtd0NFZW1VdnMyZz09