Possible quenching of static neutron pairing near the N=98 deformed shell gap: Rotational structures in Gd160,161

Abstract

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Decay spectroscopy of Eu160 : Quasiparticle configurations of excited states and structure of Kπ=4+ bandheads in Yates1, Krüecken2, Dillmann3 et al. 2023Phys. Rev. C0000View full textAdd to dashboardCite

“…The minimized mixing ratio occurs at δ = 0.41 (10). their recent publication using Coulomb excitation of 160 Gd [8] this state was firmly established as a member of the γ band.…”

“…4. From this spectrum, a relative intensity of I γ = 0.26 (8) was determined. Although this transition is highly converted (α = 7.314 [16]), the low γ -ray intensity and low conversion electron detection efficiency resulted in no observed conversion electron signal for this transition in PACES.…”

“…The 4 + state at 1070.8 keV (the "4 + I " state) and the 4 + state at 1483.4 keV (the "4 + II " state) are both bandheads of K π = 4 + bands. The band built on the 4 + I state was recently extended up to angular momentum 18 h [8]. While the K π = 4 + bands in even-even rare-earth nuclei were originally interpreted as double-γ phonons, it was pointed out by Burke [7] that the experimental evidence from transfer reaction studies and transition rates is more consistent with these bandheads being hexadecapole phonons.…”

“…The newly measured enhanced B(E 2) values between the two 4 + states are consistent with a strong overlap in wave functions of the two 4 + states. However, a strong two-level mixing scenario for just the bandheads or the first few states of the rotational bands seems to be at odds with the interpretation that the rotational band built on the 4 + I state is dominated by the ν 2 (5/2[523], 3/2[521]) two-quasineutron configuration above spin 6 h [8], based on the observed small B(M1)/B(E 2) ratios. If only the 4 + bandheads were to be mixed strongly with an interaction of V ≈ 200 keV, the rotational structure of the band would be changed significantly near the bandhead due to the large energy shift of the 4 + state.…”

“…The K π = 4 + bands in 160 Gd have bandheads at 1070.8 and 1483.4 keV, and are strongly populated in the β decay of the J π = (5) β-decaying state of 160 Eu. The lower K π = 4 + band was further studied by Hartley et al [8] via unsafe Coulomb excitation, extending the rotational band built on the 1070.8-keV 4 + state to I π = 18 + . In that study, an unusual alignment behavior was identified and interpreted as resulting from a quenching of static neutron pairing with a predominant two-quasineutron configuration.…”