Deformation change in light iridium nuclei from laser spectroscopy

Abstract

Laser spectroscopy measurements have been performed on neutron-deficient and stable Ir isotopes using the COMPLIS experimental setup installed at ISOLDE-CERN. The radioactive Ir atoms were obtained from successive decays of a mass separated Hg beam deposited onto a carbon substrate after deceleration to 1kV and subsequently laser desorbed. A three-color, two-step resonant scheme was used to selectively ionize the desorbed Ir atoms. The hyperfine structure (HFS) and isotope shift (IS) of the first transition of the ionization path 5d 7 6s 2 4 F 9/2 → 5d 7 6s6p 6 F 11/2 at 351.5 nm were measured for 182−189 Ir, 186 Ir m and the stable 191,193 Ir. The nuclear magnetic moments µI and the spectroscopic quadrupole moments Qs were obtained from the HFS spectra and the change of the mean square charge radii from the IS measurements. The sign of µI was experimentally determined for the first time for the masses 182 ≤A≤ 189 and the isomeric state 186 Ir m. The spectroscopic quadrupole moments of 182 Ir and 183 Ir were measured also for the first time. A large mean square charge radius change between 187 Ir and 186 Ir g and between 186 Ir m and 186 Ir g was observed corresponding to a sudden increase in deformation: from β2 +0.16 for the heavier group A=193, 191, 189, 187 and 186m to β2 ≥ +0.2 for the lighter group A=186g, 185, 184, 183 and 182. These results were analyzed in the framework of a microscopic treatment of an axial rotor plus one or two quasiparticle(s). This sudden deformation change is associated with a change in the proton state that describes the odd-nuclei ground state or that participates in the coupling with the neutron in the odd-odd nuclei. This state is identified with the π3/2 + [402] orbital for the heavier group and with the π1/2 − [541] orbital stemming from the 1h 9/2 spherical subshell for the lighter group. That last state seems to affect strongly the observed values of the nuclear moments.

Shape coexistence in Au187 studied by laser spectroscopy

“…Indeed, it was shown that the PTRM calculations [10] successfully described the nuclear spectroscopic data for 187 Au with the assumption that the 9/2 − isomer in 187 Au is the band head of a strongly Coriolis-perturbed rotational band built on the π 1/2 − [541]h 9/2 Nilsson orbital, at a moderate prolate deformation. Similar ground-state bands with anomalous spin sequences were also found, e.g., in 183,185 Au (5/2 − band head) [43,44], 181,183,185 Ir (5/2 − band head) [45][46][47][48], 219 Fr (9/2 − band head) [49], and 221 Fr (5/2 − band head) [50].…”

“…where g l and g s are the orbital and spin g factors, respectively. The experimental situation when the I π = 9/2 − state becomes the lowest band member corresponds to a very high effective decoupling parameter, a eff dec ≈ +8, whereas its maximal theoretical value is a dec = +5 [48]. This increase provides evidence for a supplementary perturbation coming from the nondiagonal term of the Coriolis interaction [51].…”

Electronic isotope shift factors for the Ir 5d76s24F9/2Schiffmann1, Godefroid2 2021Journal of Quantitative Spectroscopy and Radiative Transfer6100View full textAdd to dashboardCite

“…Note that we used expression (8) and not (9) for the field shift, which is consistent with the approach adopted in Ref. [43] where the isotope shifts are calculated according to…”

“…Another experimental paper dedicated to isotope shifts in neutral iridium was published by Verney et al[43] .They reported IS values for a long chain ofA Ir isotopes A = 193 , 191 , 189 , 187 , 186 m, 186 g, 185 , 184 , 183 , 182 , for the 5 d 7 6 s 2 4 F 9 / 2 → 5 d 7 6 s 6 p 6 F o 11 / 2 transition at 351.5 nm, where the 6 F o 11 / 2 level is the lowest of the J π = (11 / 2) o symmetry. They reported a field shift parameter of F 0 , 351 = −31 .…”

Decay of 185Tl, 185m+gHg, 189m+gPb and energy location of the 13/2+ isomeric states in 185Hg, 189Pb, 193Po and 197Rn

“…For these elements, states corresponding to a rather large nuclear deformation appear suddenly for a a e-mail: sauvage@ipno.in2p3.fr mass number A < 187 [1][2][3][4][5][6][7], giving rise to shape or deformation change between neighbouring isotopes and/or to coexistence of states having different nuclear shapes or deformations in one nucleus. The most spectacular examples of shape coexistence have been discovered in the 185,186 Hg nuclei where states corresponding to very different deformation parameters, |β| = 0.15 and |β| = 0.25, coexist at low excitation energy [1,2].…”