A reanalysis of (p, p') data taken on 2+i and 3, states of 37 even-even A )40 nuclei at energies of E (50 MeV has been performed with a consistent procedure involving coupled-channels calculations and Becchetti-Greenlees optical model parameters. The matrix elements extracted from this analysis have been compared to matrix elements deduced from electromagnetic measurements of the same excitations. It is concluded that the differences between (p, p') and electromagnetic results which are often observed do not result from variations in the method of analysis of the (p, p') data. Instead, the differences are caused by experimental errors and nuclear structure effects. The nuclear structure effects are examined by extracting the ratios M"/M"of the neutron and proton multipole matrix elements for both the 2i and 3i states from the proton and electromagnetic data. PACS number(s): 21.60.Ev, 25.40.Ep, 23.20.Js
A study of fragmentation of the low energy octupole state is performed in order to study the dependence of this fragmentation on quadrupole deformation, determine the limitations of surveys of 3& states, and search for exceptional cases of fragmentation. A regular dependence of fragmentation on the deformation parameter P, is found, and it is demonstrated that the large degree of fragmentation observed in ' ' ' 'Pt is indeed unique. In many nuclei, which are generally spherical or weakly deformed, a large concentration of E3 strength occurs' in a single 3 state (the low energy octupole state) which exists at an energy below 4 MeV. However, in many deformed nuclei this strength fragments among several 3 states. These states often correspond to different alignments of the octupole phonon (E =0, l, 2, and 3) with respect to the symmetry axis of the deformed nucleus. Substantial fragmentation has also been observed in several nuclei which are not well deformed.This fragmentation of octupole strength can pose a significant problem in studies of the systematic behavior of the energies of 3& states, a number of which have been reported recently.In most regions of the Periodic Table, 3, state energies vary smoothly with both N and Z. Authors of the systematic studies generally aim to search for interesting nuclear structure phenomena by identifying octupole behavior which deviates from the usual smooth trends. For example, information on single-particle energies in the A =130 region has been obtained, and anomalous behavior in the heavy Cd isotopes has been demonstrated.However, the fragmentation which is well known to occur in many rare-earth and actinide nuclei has prevented extensive analysis of octupole behavior in these regions (limited analyses are performed in Refs. 4 -6).In addition, fragmentation was found to be responsible for an apparent anomaly in octupole behavior which occurs in the Pt (Z =78) and Hg (Z =80) isotopes near N =120, which are not well deformed. The energies of the 3, states in these Pt isotopes are approximately 1 MeV below those in the Hg isotopes; ' such a discontinuity does not occur anywhere else in the Periodic Table. Shortly after this anomaly was identified, strong and previously unknown 3 states were found 1 MeV above the 3, states in the N = 116 -120 isotopes Pt. When the centroids of octupole strength of nuclei in the vicinity of Pt were examined (instead of the 3, states), the usual smooth systematic behavior was found to occur. Octupole centroids have also been used for systematic analysis in the region near A =150. That study demonstrated the effects of the collapse of the Z =64 shell gap on octupole behavior in that neighborhood of nuclei.In the present article, we survey available data on fragmentation of the low energy octupole states in A )60 nuclei. This work was initiated with three objectives. First, it is interesting to determine the dependence of octupole fragmentation on quadrupole deformation. Second, it is important to determine in which nuclei the centroid of the low ...
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