Evidence for Collective Oblate Rotation inN=Z68Se

Abstract

A gamma-ray spectroscopic measurement of the N = Z nucleus 68Se has been made following the 12C(58Ni,2n) reaction at 185 and 220 MeV using Gammasphere and the Argonne Fragment Mass Analyzer. Despite a very low production cross section of 200(50) &mgr;b, two distinct rotational bands were found; the ground state band consistent with oblate collective rotation, and an excited band consistent with prolate rotation. These observations support long-standing predictions that nuclear ground states with substantial oblate (beta(2) approximately -0.3) deformation should exist in this region.

Symmetry-unrestricted Skyrme–Hartree–Fock–Bogoliubov calculations for exotic shapes in nuclei from 64Ge to 84Mo

“…These gross features are consistent with available experimental data [60][61][62][63][64][65][66] and previous theoretical calculations [19,21,22,49,[67][68][69][70][71][72][73][74][75][76][77].…”

“…Quite recently, an excited prolate band coexisting with the ground-state oblate band has been found in 68 Se [63]. Their quadrupole deformations are estimated as β 2 ≈ 0.27 and β 2 ≈ −0.27, respectively.…”

“…1, but it is only about 0.3 MeV in the plot with respect to the triaxial deformation parameter γ in Fig.2. It might be considered that, if the barrier is so low, the two bands built on the prolate and the oblate solutions interact strongly so that the shape coexistence picture is too much perturbed in contradiction with the experiment [63]. In our view, however, description of dynamics by going beyond the static meanfield approximation is necessary in order to discuss the interaction between the oblate and the prolate structures.…”

Shape coexistence inSe72investigated following theβdecay ofMcCutchan1, Lister2, Ahn3 et al. 2011Phys. Rev. CSelf Cite212230View full textAdd to dashboardCite

“…Shape coexistence in the light Selenium isotopes has been the subject of intense debate in the last few years, with evidence presented for oblate ground states [1,2], which was challenged [3], supported [4], and once more cast in doubt [5]. Independent of the interpretation of the ground state structure, the dynamic behavior becomes dominated by prolate collective rotation, at modest (∼1 MeV) excitation energy.…”

“…Figure 1 illustrates these unusual features with a plot of 2I/h 2 versus (hω) 2 for the ground state bands of 68,70,72,74 Se. 68 Se has a smoothly evolving band interpreted [1] as collective oblate rotation. In 70,72 Se, the low-spin states are significantly perturbed, while the states with J > 6 follow the behavior expected for a rotational band with constant moment of inertia and constant deformation.…”