Electric quadrupole strength in 20Ne from the 19F(p

Abstract

The cross sections and analyzing powers of the $^{19}$F(p\ensuremath{\rightarrow},${\ensuremath{\gamma}}_{0}$${\ensuremath{\gamma}}_{1}$${)}^{20}$Ne reactions have been measured with high precision at nine angles for 24 incident proton bombarding energies in the range 3.5--13.3 MeV, corresponding to excitation energies in $^{20}\mathrm{Ne}$ of 16.0 to 25.5 MeV. At each energy, the E1 and E2 transition matrix elements were determined from a partial wave analysis of the angular distributions of ${\ensuremath{\gamma}}_{0}$. For excitation energies above 23.5 MeV, the calculated direct capture E2 strength can account for most of the measured strength. However, a sizable E2 strength in excess of direct capture was measured for ${E}_{\ensuremath{\gamma}}$\ensuremath{\le}23.5 MeV. Our results indicate that \ensuremath{\approxeq}9% of the isoscalar E2 sum rule is exhausted in the (${\ensuremath{\gamma}}_{0}$,${\mathrm{p}}_{0}$) reaction for excitation energies from 16.0 to 25.5 MeV. A comparison with (\ensuremath{\alpha},\ensuremath{\alpha}') results shows for the first time essential agreement between E2 strengths observed with the two modes of excitation. The analysis of the (p,${\ensuremath{\gamma}}_{0}$) data reveals strong evidence for an M1 resonance near an excitation energy of 17.7 MeV. The analysis of angular distribution measurements for the ${\ensuremath{\gamma}}_{1}$ decay channel is also reported.