Observation of double electron-positron pair production by `gama´ rays reexamined - Maidana, Nora Lia; Brualla, L; Oliveira, José Roberto Brandão de; Rizzutto, Márcia de Almeida; Added, Nemitala; Fernandez-Varea, J M; Vanin, Vito Roberto (Physical Review C, 2009)