Isovector giant quadrupole resonance observed in Si30(p,)31P
The Si30(p,)31P reaction has been studied in the proton energy range Ep=2036 MeV. Angular distributions of the cross section and the analyzing power have been measured for -ray transitions to the ground state and the first excited state of P31 over the angular range 37.5°145°at Ep=25.5 MeV. Legendre polynomial fits to both observables yield nonzero coefficients of order k=3,4, suggesting the interference of E2 radiation with the dominant E1 radiation. A transition-matrix-element analysis of the data indicates that 26% of the 1 cross section at this energy arises from E2 radiation, whereas only 10% of the 0 cross section can be attributed to E2 radiation. Direct-semidirect calculations give a direct E2 component of 7% for both channels, suggesting significant excess E2 strength in the 1 channel at this energy. The energy dependence of the 90°analyzing power for 1 shows a resonance structure near Ep=34 MeV which can be reproduced by a direct-semidirect calculation including an E2 resonance at EGQR=38.6 MeV with a width of GQR=5.0 MeV and a strength of 50% of the isovector E2 energy-weighted sum rule. The current results thus provide strong evidence for collective E2 strength roughly at the expected peak of the isovector giant quadrupole resonance built on the first excited state of P31. © 1991 The American Physical Society.
Feldman, G; Kramer, LH; Weller, HR; Hayward, E; Dodge, WR
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