Hello Saeed, Yes you can disable the optical photons data in the root output file with the following command: <pre> /gate/output/root/setRootOpticalFlag 0 or 1 </pre><a href="http://wiki.opengatecollaboration.org/index.php/Users_Guide_V6.2:Generating_and_tracking_optical_photons">http://wiki.opengatecollaboration.org/index.php/Users_Guide_V6.2:Generating_and_tracking_optical_photons</a> You need to update your gate code with the latest version of the tarball from <a href="http://www.opengatecollaboration.org/releasedownload">http://www.opengatecollaboration.org/releasedownload</a>. vesna <div class="gmail_quote">On Sun, Dec 9, 2012 at 3:31 PM, Saeed Heidary <<a href="mailto:saeedheidary79@gmail.com" target="_blank">saeedheidary79@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> Dear GATE users Is there any resolution to stop producing optical photons in root outputs! It causes producing a huge volume of a root file! things like what is done for Singles or Hit (/gate/output/root/setRootHitFlag 0 /gate/output/root/setRootSinglesFlag 0). Many thanks </blockquote></div>