Low-lying proton intruder state in 13B

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