Geant4 - A Simulation Toolkit, Nuclear Physics News, Volume 17 Issue 2, 20 (Author Posting. (c) Taylor & Francis, 2007. This is the author's version of the work. It is posted here by permission of Taylor & Francis for personal use, not for redistribution. The definitive version was published in Nuclear Physics News, Volume 17 Issue 2, April 2007. doi:10.1080/10506890701404297 (http://dx.doi.org/10.1080/10506890701404297)).