High-resolution (e, e') study of isovector M1 and M2 transitions in the oxygen isotopes: (I). 16O

Abstract

The M1 and M2 transition strength distribution for 16O in the excitation energy range from 16 to 20 MeV has been measured in a high-resolution electron scattering experiment. The M1 strength is concentrated in three sharp states at E x = 16.22, 17.14 and 18.79 MeV (± 0.01 MeV) with B(M1, k)↑ = 0.20 ± 0.02, 0.32 ± 0.03 and 0.13 ± 0.03 μ N 2, respectively. An additional strength of 0.35 ± 0.09 μ N 2, distributed over eight weakly excited states with excitation energies E x = 17.4 to 18.0 MeV, brings the total measured M1 strength to B(M1, k)↑ = 1.0 ± 0.1 μ N 2. The experimental M2 strength is distributed over states at E x = 16.82, 17.78, 18.50 and 19.0 MeV (± 0.01 MeV) with B(M2, k)↑ = 19 ± 2, 13 ± 2, 59 ± 7 and 341 ± 51 μ N 2 · fm 2, respectively. Electric transitions were also measured to states at E x = 16.45 MeV (2 +, E2), 17.30 MeV (1 +, E1) and 18.20 MeV (2 +, E2). Calculations were performed using the modified surface delta interaction in a 2p-2h shell model for the M1 transitions and the random phase approximation for the M2 transitions. The results show the sensitivity of the M1 strength as a measure of ground-state correlations and compare well with results from the 15N( p , γ) reaction.