Neutron decay from the giant resonance via the 10B(e,e'n) reaction

The cross sections and angular correlations for neutron decay into various states in the residual nucleus following the 10 B(e,e'n) reaction have been measured over the excitation energy range of 18-33 MeV at an effective momentum transfer of 0.56 fm -1 . In the giant resonance, neutron emissionleads to the population of two higher excited states in addition to the ground-state transition: 6.97 MeV 7/2 - (n 5 ) and 11.70 MeV 7/2- + 12.06 MeV 3/2 - (n 6 , 7 ). This is the first observation of the neutron population of these states. The angular correlations for n 0 show a strong forward-backward asymmetry, which suggests interference from a transition with the opposite parity to E1. The angular correlations for n 5 and n 6,7 have a peak shift of about 50° at lower excitation energy and recover above about 24 and 25 MeV for n 5 and n 6,7 , respectively. Their patterns are considerably different from that for n 0 . The angular correlations for each transition were fitted with a Legendre polynomial. The longitudinal-transverse interference coefficient C 2 /A 0 is negligible for all populations. For n 0 decay, all Legendre coefficients b i are positive, but b 2 and b 3 for the n 5 and n 6,7 decays are negative at lower excitation energy, and the latter causes a shift of the forward peak. The negative values may come from the signs of the phase differences of cos δ 21 and cos δ 20 . The 10 B(e,e'n) cross section measured up to E x∼ 32MeV agrees well with that of 10 B(γ,n), except for a peak at 23 MeV of the giant resonance. In comparison with shell-model calculations, the partial cross section for n 0 is sizable up to higher excitation energy, and predicted large partial cross sections populating the 6.97 MeV 7/2 - and 11.70 MeV 7/2- + 12.06 MeV 3/2- states in the giant resonancewere not observed.