Two-particle three-hole structure of negative-parity states in 15N

Abstract

The 2p-3h character of negative-parity states of 15N was studied using the two-particle transfer 13C( 3He, p) 15N reaction. Absolute differential cross sections were measured at 5 MeV bombarding energy for all excited states below 8 MeV and for the 9.05, 9.152+9.155 and 9.22 MeV states. According to a two-particle DWBA analysis of these angular distributions, the 9.22 MeV state is assigned negative parity. From γ-γ angular correlation measurements of the 9.22–6.32–0 MeV cascade decay, a preferred spin value of 1 2 is found for this state. This is the first excited state in 15N of the same J π as the ground state. The Doppler-shift attenuation method was applied to Ge(Li)γ-ray spectra to obtain lifetimes of ≦ 100 fs for states from 7 to 10 MeV excitation in 15N. Analog states in 15N and 15O are identified with corresponding theoretical negative-parity states for the A = 15 system. The DWBA analysis indicates that the 9.22 MeV state has the configuration ( lp) −3(2 s 1 2 ) 2 and that the 9.152 MeV state is a mixture of the configurations ( lp) −3(2 s 1 2 ) 2 and ( lp) −3( ld 5 2 ) 2 . Small but significant admixtures of 2p-3h configurations are required to account for the measured angular distributions for the ground and 6.32 MeV states.