Angular distribution and correlation measurements on 15N(p,γ012)O16 in the region Esub(x)=18-33 MeV and an excited-state giant resonance in 16O

Previous data on excitation functions for 15N(p,γ1 + γ2)16O have been extended to cover the energy range Esub(p)=6-22 MeV (Esub(x)=18-33 MeV). In addition, angular distribution measurements have been made throughout this range, and γ-γ angular correlation measurements made over the region of a resonance at Esub(p)=8.86 MeV. From the data, and from comparison with other work, spin assignments are made for resonances as follows: Esub(x)=18.02 MeV, J=3; Esub(x)=18.98 MeV, J=2, 4; Esub(x)=19.90 MeV, J=3; Esub(x)=20.43 MeV, Jsup(π)=2-; Esub(x)=24.77 MeV, Jsup(π)=2+, 4+; Esub(x)=26.42 MeV, Jsup(π)=2+, 4+ and Esub(x)=27.36 MeV, Jsup(π)=2+, 4+. Radiative widths are also deduced. The region Esub(x)=23-32 MeV is identified as a giant dipole resonance on the 6.13 MeV, Jsup(π)=3-, T=0 state of 16O from angular distribution measurements. The nature of this giant resonance is discussed and it is compared with the ground-state giant dipole resonance; it is shown that the main part of the excited-state giant resonance can be accounted for by broad states with Jsup(π)=2+ and 4+ with configuration (1psub(1/2)-1 (2p, 1f)) in this region. (Auth.)