First observation of β-delayed proton decay of the proton drip line nuclide 19Na

19Na, a nuclide on proton drip line, was studied by 20Ne(p,2n)19Na reaction. Experiment was performed on the proton linear accelerator at Institute of High Energy Physics, The Chinese Academy of Sciences. The new decay mode of β-delayed proton decay was observed for the first time. The half-life of 19Na was determined to be 47 +- 20 ms and its proton energy was measured to be 1.10 +- 0.-08 MeV which is corresponding to super-allowed beta transition of 19Na to excited state of 7.62 MeV, the isospin analog state with T = 3/2 in 19Ne, and subsequent proton emission to the ground state of 18F