a Study of the Giant Quadrupole Resonance of Neon -20 with Polarized Proton Radiative Capture.
Abstract
The giant quadrupole resonance of ('20)Ne was studied by means of radiative capture of polarized protons on ('19)F. To investigate the energy dependence of the E2 strength, a nine point angular distri- bution of cross sections and analyzing powers of the ('19)F((')p,(gamma))('20)Ne reaction was measured with high precision for 25 incident proton bombarding energies in the range 3.5 to 13.3 MeV, corresponding to excitation energies in ('20)Ne of 16.2 to 25.5 MeV. In the ('19)F((')p,(gamma)(,0))('20)Ne reaction leading to the 0('+) ground state of ('20)Ne, a polarized angular distribution allows a model independent determination of the com- plex reaction matrix elements for E1 and E2 radiation, and thus of the E1 and E2 strengths, provided we assume that E1 and E2 are the only significant multipole radiations involved in the reaction. For the first excited state of ('20)Ne, the determination of E1 and E2 amplitudes cannot be made in a model independent manner because the higher angular momentum of the final state (J('(pi)) = 2('+)) allows too many proton partial waves. Almost all of the cross section and analyzing power angular distributions are consistent with the assumption of only E1 and E2 radiation, except for those around excitation energy (DBLTURN) 17.7 MeV, where the analysis reveals evidence for an M1 resonance. In the energy region studied here, the E2 strength was measured to be on the order of 0.5 (mu)b and varies from (TURN)2% to (TURN)15% of the total cross section at E(,(gamma)) (TURN) 18.5 MeV and (TURN)25.5 MeV, respectively. In ('20)Ne both the E1 and E2 strengths show doorway structure, although for the E2 strength it appears to be less pronounced. The calculated direct capture E2 strength can account for most of the measured strength for E(,(gamma)) (GREATERTHEQ) 23.5 MeV. However, a sizable E2 strength in excess of that calculated for direct capture was measured for E(,(gamma)) (LESSTHEQ) 23.5 MeV. The measured E2 energy weighted sum rule of the ('19)F((')p,(gamma)(,0))('20)Ne reaction for excitation energies of 15.8 to 25.6 MeV exhausts 9.2 (+OR -) 0.8% of the total isoscalar E2 energy weighted sum rule. This is comparable to a recent ('20)Ne((alpha),(alpha)'p) measurement. The location of the E2 strength found in the present work is consistent with that found in a study of the ('20)Ne((alpha),(alpha)')('20)Ne reaction.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1986
- Bibcode:
- 1986PhDT........64W
- Keywords:
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- Physics: Nuclear