Angular distribution and correlation measurements on 15N(p, γ 0, 1, 2) 16O in the region Ex = 18–33 MeV and an excited-state giant resonance in 16O

Abstract

Previous data on excitation functions for 15N(p, γ 1 + γ 2) 16O have been extended to cover the energy range E p = 6–22 MeV ( E 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 E p = 8.86 MeV. From the data, and from comparison with other work, spin assignments are made for resonances as follows: E x = 18.02 MeV, J = 3; E x = 18.98 MeV, J = 2, 4; E x = 19.90 MeV, J = 3; E x = 20.43 MeV, J π = 2 −; E x = 24.77 MeV, J π = 2 +, 4 +; E x = 26.42 MeV, J π = 2 +, 4 + and E x = 27.36 MeV, J π = 2 +, 4 +. Radiative widths are also deduced. The region E x = 23–32 MeV is identified as a giant dipole resonance on the 6.13 MeV, J π = 2 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 J π = 2 + and 4 + with configuration (1 p −1 1 2 (2 p, 1 f)) in this region.