Electric quadrupole strength inO16from theN15(p→,γ0)16O reaction reaction

Angular distributions of the relative cross sections and analyzing powers have been measured for the ${}_{}{}^{15}{}_{}{}^{}\mathrm{N}$(p→,${\gamma }_0$ ${)}^{16}$O reaction in ≊500 keV steps for excitation energies in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ between 17.8 and 24.9 MeV. All E1 and E2 transition matrix elements were determined using a partial-wave analysis. Below 22 MeV, little quadrupole strength was found in excess of that predicted in direct capture calculations. A clear enhancement of the E2 cross section was observed at energies above 22 MeV. Our data indicate that about 10% of the isoscalar E2 sum rule for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ is exhausted in the ${\mathrm{p}}_0$ decay channel between 18 and 25 MeV, with approximately (3/4 of this integrated strength concentrated between 22 and 25 MeV. The E2 strength seen in (γ,${\mathrm{p}}_0$) is strikingly different from that observed in (α,α’) or (α,α’p). The effect of the M1 state at $E_x$=18.8 MeV previously found in (p,γ) studies is clearly observed.