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HK: Hadronen und Kerne
HK 56: Postersitzung
HK 56.1: Poster
Wednesday, March 18, 1998, 17:00–19:00, Foyer
Identification of the First Members of a Negative-parity “Inversion Doublet” Band in 18O — •F. Michel1 and G. Reidemeister2 — 1Université de Mons-Hainaut, Belgium — 2Université Libre de Bruxelles, Belgium
In the 18O nucleus, shell model states are known to coexist with low-lying, deformed particle-hole excitations. The lowest of these deformed states group into a quasi-rotational band built on the 4p - 2h, Jπ=0+, Ex = 3.63 MeV state. This band appears to be the close analogue of the 20Ne ground state band and of the 4p - 4h excited band in 16O. While in these two cases, the existence of an “inversion doublet”, negative parity band, located at higher energy — and thus decoupled in parity from the positive-parity α-cluster band — is well established, the situation remains controversial in the 18O nucleus. On the basis of a global optical model analysis of 14C(α,α0) scattering above 20 MeV, we have suggested that such a negative parity band should exist above the α + 14C threshold.
We have subjected the available elastic scattering excitation functions between 2 and 7.5 MeV laboratory energy to a detailed resonance + background analysis. Among other results, our analysis points to a rapid evolution of the ℓ = 1 background phase shift in the energy region where a broad state has been observed in the β-delayed α-particle decay of 18N. This state appears to be a natural candidate for the bandhead of the negative-parity “inversion doublet” band in 18O.