How large is the spreading width of a superdeformed band?

Abstract

Recent models of the decay out of superdeformed bands can broadly be divided into two categories. One approach is based on the similarity between the tunneling process involved in the decay and that involved in the fusion of heavy ions, and builds on the formalism of nuclear reaction theory. The other arises from an analogy between the superdeformed decay and transport between coupled quantum dots. These models suggest conflicting values for the spreading width of the decaying superdeformed states. In this paper, the decay of superdeformed bands in the five even-even nuclei in which the SD excitation energies have been determined experimentally is considered in the framework of both approaches, and the significance of the difference in the resulting spreading widths is considered. The results of the two models are also compared to tunneling widths estimated from previous barrier height predictions and a parabolic approximation to the barrier shape

Decay-out properties of a linked superdeformed band inZr84

“…These values of ↓ are several orders of magnitude larger than in 152 Dy or in the A ≈ 190 region; of the cases considered, only 192 Pb is comparable, with ↓ ∼ 1 keV scale (see Table II of Ref. [18]). In fact, the four quantities S , N , d, and ↓ in 84 Zr all extend the previously observed ranges to larger values, exploring a different regime from that accessed by the A ≈ 150 and 190 studies.…”

“…In fact, the four quantities S , N , d, and ↓ in 84 Zr all extend the previously observed ranges to larger values, exploring a different regime from that accessed by the A ≈ 150 and 190 studies. The ND level spacing for 84 Zr is up to two orders of magnitude larger than in the A ≈ 150 and 190 cases considered [18], and thus there are fewer ND states available with which the SD states can mix; however, the ND states in 84 Zr also have much larger decay widths. The ratio N /d, which is relevant in the GW model, is about 1-2 orders of magnitude larger in 84 Zr than in 192 Pb, yet the spreading widths are comparable.…”

“…Statistical-decay models have been applied in the interpretations of the weak SD decay out in 152 Dy and several A ≈ 190 nuclei (see Ref. [18] and references therein); the similarities between 84 Zr and those heavier SD nuclei suggest that a related approach can be used here. The decays observed between the SD and ND bands, which are associated with very different configurations and shapes, could in this way be explained as arising from small admixtures of several different configurations.…”

Microscopic description of nuclear structure aroundZr80

“…The decay out is actually attributed to a mixing of the SD states with the ND (or spherical) states with equal spin, which are close in energy to the SD states (more precisely, with the excited compound states which are located several MeV above the yrast ND states [71][72][73][74]). Because the typical energy difference between the SD states and ND (spherical) states is as high as 6-8 MeV for 82 Zr and 84 Zr nuclei at high spins, the decay-out intensity should be rather fragmented, as those found in A = 150 and 190 mass regions [75][76][77][78][79].…”

Intensity profiles of superdeformed bands in Pb isotopes in a two-level mixing model

“…To date, no conceptual objections have been raised to the model; however, there has been some debate as to whether the decay can adequately be described in terms of mixing with a single level in the primary minimum [14][15][16] (or whether mixing with a single compound level is the equivalent of statistical mixing with many levels). The model has been successfully used to extract tunneling widths between the SD and ND wells [17] and to examine the abruptness of the onset of decay [18].…”