- Godwin, MA; Hayward, E; Feldman, G; Kramer, LH; Weller, HR; Dodge, WR
- The cross section and vector analyzing power for transitions to the ground and low-lying states in the Y89(p,)90Zr reaction have been studied over the angular range =38.8°130°at Ep=22.5 MeV and over the energy range Ep=18.5 28.5 MeV at =90°. Angular distributions for the 0 and 1+2+3 transitions (i.e., to the first three strong single-particle excited states) reveal large asymmetries about =90°in both () and ()Ay(), suggesting E1/E2 interference effects. Legendre polynomial fits to these data yield nonzero coefficients of order k=3,4, thus confirming interference between the dominant E1 radiation and opposite parity E2 radiation. A transition-matrix element analysis of the 0 angular distribution data, including E1 and E2 radiation, suggests a 28% E2 contribution, while a pure direct capture calculation predicts only 12% E2 strength. The energy dependence of Ay(90°) for the 123 data is adequately described using the direct-semidirect model by including isovector quadropole resonances at EGQR=27.5 MeV, built on each of the three states, with widths of GQR=7.0 MeV and strengths which exhaust 100% of the isovector E2 energy-weighted sum rule for each state. These results provide strong evidence for collective E2 strength built on excited states in Zr90, approximately at the energy predicted for the isovector giant quadrupole resonance, but are inconclusive concerning the ground-state transition. © 1994 The American Physical Society.
- January 1, 1994
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