A coincidence study of electron and positron impact ionization of Ar (3p) at 1 keV Radu I. Campeanu, James H.R. Walters and Colm T. Whelan Eur. Phys. J. D, 69 10 (2015) 235 Published online: 29 October 2015 DOI: 10.1140/epjd/e2015-60315-1