First evidence ofγcollectivity close to the doubly magic coreSn132

Abstract

The138 Te and 140 Xe nuclei have been reinvestigated using prompt γ-ray data from spontaneous fission of 248 Cm, collected with the EUROGAM2 Ge array. γ bands have been identified in both nuclei. The γ band observed in 138 Te, a nucleus with only 6 valence nucleons, indicates the presence of collectivity very close to the doubly-magic 132 Sn core. Such band is even more pronounced in 140 Xe, the N=86 isotone of 138 Te. The newly observed bands are interpreted within the shell model, which reproduce well the γ collectivity at N=86.

Spectroscopy and lifetime measurements in Te134,136,138 isotopes and implications for the nuclear structure beyond N=82Häfner1, Lozeva2, Naïdja3 et al. 2021Phys. Rev. CSelf Cite93180View full textAdd to dashboardCite

“…Literature values represent 248 Cm fission data taken from Refs. [24,49,51]. Unobserved energies as taken from Ref.…”

“…Apart from the wellknown 134 Te, up to now, no direct lifetime measurement for states above the 2 + 1 in 136 Te are reported in the literature. Excited states in 138 Te have been observed through spontaneous fission of 248 Cm [15,24] and β decay of 138 Sb [17] but no information on lifetimes of low-lying excited states has been reported. The interplay between collective excitations and the single-particle nature of nuclei with few valence particles is expected to result in sub-ns low-lying excited states that are accessible through fast electronic timing.…”

Measurement of picosecond lifetimes in neutron-rich Xe isotopes

“…The increase in collectivity is interpreted as the "shape" phase transition from spherical vibrator at N = 82 towards an axially symmetric rotor for N > 82. The lack of axial asymmetry in this calculation could explain the discrepancy with the experimental value for 140 Xe in the light of new evidence of γ collectivity found in this nucleus by Urban et al [28]. A triaxial shape with (β,γ ) parameters (0.15,15.5…”

Coulomb Excitation of $^{142}$Xe

“…Moreover, given the fact that a candidate for a gamma band in 140 Xe was found [10], it would not be too surprising to find a second 2 + state in the given energy range, especially as 2 + states are readily populated by Coulomb excitation. Figure 2 shows the spectrum of only those gamma rays which were detected in coincidence with the backwards facing DSSSD.…”