Dear Developers, We are concerned that there is something wrong with Gate_v3.1.2. We have been running simulations for quite a long time using Gate_v3.1.1 and recently we have installed the new version of Geant (v4.9.0_p01 ) and ROOT (v5.14.00) together with Gate_v3.1.2. The results we obtain running the same simulations as before, totally defer from each other. The simulation parameters are as follows: Cubic water phantom 30x30x30cm, not voxelized or voxelized in 1cm or 0.4cm cubic voxels, center in (0,0,0) The source is in the center (0,0,0), slightly translated with 1e-7cm to avoid setting up the source on the intersect between voxels Source activity is 1e6 bq. The simulation Run is 10s long. We are using General Electric scanner. We are interested in the total singles and coincidences produced by the simulations. The number of singles we obtain from both versions match quite well. But the problem is that the number coincidences (true scattered and true unscattered) differ from each other by an order of magnitude, which in our opinion is quite disturbing. Performing one and the same simulation (with exactly the same mac files in exactly the same directory) with one and the same initial random seeds gives a huge difference in the number of coincidences, which obviously is statistically significant. An example is shown below: *** Gate_v3.1.1 *** Phantom: WaterBox, 1.0cm Vox Singles: 708469 Random Coins.: 109 True Unscattered Coins.: 27304 True Scattered Coins.: 17191 Total: 44604 Events: 9995991 *** Gate_v3.1.2 *** Phantom: WaterBox, 1.0cm Vox Singles: 717897 Random Coins.: 111 True Unscattered Coins.: 2497 True Scattered Coins.: 5355 Total: 7963 Events: 9998927 Some time ago we have also noticed 2 more problems, this time with Gate_v3.1.1: 1) We have prepared simulation files (again we were interested in the number of singles and coincidences produced). Running the simulation gave us a set of results (let's call them 'Results1'). Then, changing ONLY the line: /control/verbose 0 to: /control/verbose 2 Gave us another set of results (let's call them 'Results2'). It was quite interesting to find that Results1 had nothing in common with Results2. We have retested this many times and everytime the 'anomaly' was observed. What has the verbosity to do with the number of singles and coincidences produced by one and the same simulation? 2) This problem is quite similar to the one mentioned above. This time the ONLY thing we've changed in the mac files, was the name of the ROOT output file. Again the two sets of results we obtained had nothing in common. This was also retested many times. Investigating the 'anomaly' we found out that the set of results we obtain each time depends on the length of the ROOT output filename. All of the problems above where observed on two different machines. Has anyone noticed problems, similar to those above? Is there a version of Gate that is known to be stable? Any suggestions and support will be appreciated. Georgi Gerganov & Yordan Madzhunkov Bulgaria, Sofia University