Monte Carlo simulations of semi-infinite clouds of radioactive noble gases T. J. Stocki, M.-C. Lo, K. Bock, L. A. Beaton, S. D.R. Tisi, A. Tran, T. Sullivan and R. K. Ungar Radioprotection, 44 5 (2009) 735-739 Published online: 06 June 2009 DOI: 10.1051/radiopro/20095134