Nuclear Charge Radii of Neutron-Deficient Lead Isotopes BeyondN=104Midshell Investigated by In-Source Laser Spectroscopy

Abstract

The shape of exotic even-mass [182][183][184][185][186][187][188][189][190] Pb isotopes was probed by measurement of optical isotope shifts providing mean square charge radii (hr 2 i). The experiment was carried out at the ISOLDE (CERN) on-line mass separator, using in-source laser spectroscopy. Small deviations from the spherical droplet model are observed, but when compared to model calculations, those are explained by high sensitivity of hr 2 i to beyond mean-field correlations and small admixtures of intruder configurations in the ground state. The data support the predominantly spherical shape of the ground state of the proton-magic Z 82 lead isotopes near neutron midshell (N 104). The subtle interplay between individual and collective behavior of a finite number of strongly interacting fermions leads to aspects of mesoscopic systems that can only be studied in atomic nuclei [1]. For neutron-deficient nuclides around the closed proton shell at Z 82, this interplay leads to the appearance of states with different shapes at low excitation energy. These so-called shape coexisting states can be interpreted as particle-hole excitations across the closed proton shell gap [2] whereby the interaction of the valence proton particles and holes with the neutrons drives the nucleus into deformation. The phenomenon of shape-coexistence is subject to intensive experimental and theoretical studies [3,4]. Alpha-decay experiments have revealed a triplet of low-lying 0 states in the 186 Pb nucleus, which is located at neutron midshell between N 82 and 126 [1]. Excited bands built on top of the 0 states were observed in [182][183][184][185][186][187][188][189][190], and recent lifetime measurements confirmed the deformed character of the bands [11]. For 186 188 Pb, it was concluded that the ground state and the 2 1 state have a very different structure, the 0 ground state of predominantly spherical and the 2 1 state of predominantly prolate character. Monopole transition strengths between the 0 states were used to estimate the mixing between the normal and intruder configuration [12] and revealed limited configuration mixing in the 190;192;194 Pb ground-state wave function [13,14]. But as the excited 0 states become lower in energy when approaching N 104 ( 186 Pb), the mixing could increase substantially.Several theoretical models have been applied to describe the structure of the neutron-deficient lead isotopes with their coexisting and mixed spherical, prolate, and oblate states, such as phenomenological shape mixing calculations [13,14], symmetry guided shell model and interacting boson model truncations [15,16], and beyond mean-field approaches [4,17,18]. All models that provide a consistent picture of the available data suggest that the ground state of lead isotopes is dominated by spherical configurations, even when the prolate and oblate rotational bands come down very low in energy around N 104, and the barrier that separates the corresponding structures in the total energy surface is very small. But all models also ...

In-gas-cell laser spectroscopy of the magnetic dipole moment of the N≈126 isotope Pt199

“…For the heavier region 183 A 198, the prolate (183 A 188), triaxial (190 A 194), and oblate (196 A 198) shapes have been discussed and compared with theoretical models [24][25][26][27]. In the more neutron-rich region, a spherical shape is dominant toward the shell closure at N = 126 in the same way as seen for lead (Z = 82) and mercury (Z = 80) isotopes [29], predicted by the droplet model [30] with β 2 = 0. In this paper, we report experimental details and results for in-gas-cell laser ionization spectroscopy to determine the magnetic dipole moments of neutron-rich 199 Pt.…”

Ion beam production and study of radioactive isotopes with the laser ion source at ISOLDE

“…Following the series of experiments on the study of nuclear spins and electromagnetic moments of Cu isotopes [56,[78][79][80] the in-source RIS collaboration has performed extensive laser and nuclear-spectroscopic studies of isotopes in the lead region, namely the Tl [81], Pb [70,[82][83][84], Hg [45], Bi [85], Po [43,77,86,87], At and Au chains [22,88]. Our recent activity in this field has revisited the neutron-deficient Au and Hg isotopes, which were first studied at ISOLDE approximately four decades ago: the very first optical spectroscopy experiments performed at an ISOL facility [89][90][91][92].…”

Toward a global description of nuclear charge radii: Exploring the Fayans energy density functional

“…They also carry fundamental information about the saturation density of symmetric nuclear matter [2]. The local fluctuations (i.e., rapid changes as a function of particle number) in measured charge radii signal structural evolution effects, such as shell and subshell closures [3], shape deformations [4], and configuration mixing [5]. Another key structural indicator is the odd-even staggering of charge radii along isotopic chains.…”