K. F. Canter; A. P. Mills; S. Berko (1975). "Observations of Positronium Lyman-α Radiation". Phys. Rev. Lett. 34 (4): 177–180. Bibcode:1975PhRvL..34..177C. doi:10.1103/PhysRevLett.34.177.(Erratum: Phys. Rev. Lett. 34, 848 (1975))
K. F. Canter; A. P. Mills; S. Berko (1975). "Observations of Positronium Lyman-α Radiation". Phys. Rev. Lett. 34 (4): 177–180. Bibcode:1975PhRvL..34..177C. doi:10.1103/PhysRevLett.34.177.(Erratum: Phys. Rev. Lett. 34, 848 (1975))