Structure study of 12B from the elastic scattering of neutrons from 11B

Abstract

Differential cross sections for neutrons scattered from 11B have been measured for 2.2 MeV < E n < 4.5 MeV. The differential cross section σ(θ) is fitted reasonably well by R-matrix parameters for broad states in 12B with assignments 1 − and (1) + at excitation energies E x = 5.8 and 6.8 MeV respectively. The broad 1 − state has not been previously observed and is believed to be the 1 − member of the 1 p 3 2 −11 d 5 2 particle-hole multiplet predicted to exist by earlier shell model calculations. Its existence completes the identification of all of the levels of this multiplet (3 −, 2 −, 4 −, 1 −). The broad (1) + level at E x = 6.8 MeV has not been previously observed. States at excitation energies E x = 5.61, 5.73 and 6.6 MeV have been assigned spins and parities of 3 +, 3 − and (1) + respectively. These states had previously been assigned spins of 2, 3 and ≧ 1 respectively. Work on T = 1 states in 12C ∗ has been compared with the present work.