Low-lying proton intruder state in 13B

Abstract The neutron-rich nucleus 13 B was studied via the proton transfer reaction 4 He( 12 Be,  13 B γ ) at 50 A MeV . The known 4.83-MeV excited state was strongly populated and its spin and parity were assigned to 1 / 2 + by comparing the angular differential cross section data with DWBA calculations. This low-lying 1 / 2 + state is interpreted as a proton intruder state and indicates a deformation of the nucleus.