Platinum nuclei: Concealed configuration mixing and shape coexistence

Abstract

The role of configuration mixing in the Pt region is investigated. For this chain of isotopes, the nature of the ground state changes smoothly, being spherical around mass A ∼ 174 and A ∼ 192 and deformed around the mid-shell N = 104 region. This has a dramatic effect on the systematics of the energy spectra as compared to the systematics in the Pb and Hg nuclei. Interacting Boson Model with configuration mixing calculations are presented for gyromagnetic factors, α-decay hindrance factors, and isotope shifts. The necessity of incorporating intruder configurations to obtain an accurate description of the latter properties becomes evident.PACS numbers: 21.10.-k, 21.60.-n, 21.60.Fw.

Lifetime measurements in182,186Pt

“…3 [18,19], supporting a band-mixing interpretation of this B(E2) increase at low spins in these nuclei.…”

“…The shape-coexistence picture in the Pt nuclei has engendered extensive theoretical interest in recent years [15][16][17][18][19]. In particular, there has been a controversy regarding whether shape evolution in the Pt isotopes involves intruder states [17][18][19], or can be understood without invoking the intruder states [15,16].…”

“…In particular, there has been a controversy regarding whether shape evolution in the Pt isotopes involves intruder states [17][18][19], or can be understood without invoking the intruder states [15,16]. Most recently, García-Ramos et al [19] have established that configuration-mixing is an essential feature of these nuclei, although it is not apparent when considering only a limited set of data; they termed this "concealed configuration mixing" and have suggested further spectroscopic measurements where this mixing might be clearly revealed. Lifetime measurements, and the extracted transition probabilities, up to the states beyond the mixing region provide such additional spectroscopic information.…”

Shape Coexistence in the Neutron-Deficient Even-EvenHg182−188Isotopes Studied via Coulomb Excitation

“…This resulted, amongst other things, in the observation of strong staggering in the isotope shifts in the mercury isotopes [3], the discovery of triple shape coexistence in 186 Pb [4], and an early onset of deformation in the light polonium and platinum isotopes as evidenced through laser spectroscopy (see, e.g., [5]). The global trends of these experimental findings are reproduced by theoretical descriptions, such as phenomenological shape-mixing calculations and contemporary symmetry-guided models (e.g., [6,7]), and beyond mean-field approaches [5,8,9]. However, there is a lack of direct experimental information on the nature of the quadrupole deformation or on the mixing of the states belonging to the coexisting structures.…”

“…In the IBM approach [32], whereby particle-hole pair excitations across the Z ¼ 82 closed shell are explicitly included (for a similar calculation see, e.g., [6,33]), agreement between experiment and calculations for the SSM sum is noticed. However, as in the case of the BMF calculations, only partial agreement between experiment and theory is observed for the sum of triple product of IBM ME2's.…”