`end_of_day2.tar.gz` is our `work` directory at the end of day2 (Tuesday). This is where we will start from Wednesday. You can extract it by: tar -xzvf end_of_day2.tar.gz then go to the build directory, configure, build and execute: cd end_of_day2/build/ cmake ../ -DGeant4_DIR=$G4INSTALL/lib64/cmake/Geant4 make ./yourmain NOTE: there will be a segfault when you execute the program which is due to the fact that the G4RunManager is not constructed but used (i.e. nullptr when used in `YourDetectorContruction::SetTargetMaterial` that is invoked from the constructor of `YourDetectorConstruction`). You can correct this by creating the G4RunManager in `yourmain.cc` (just activate the code that is in comment there at lines #4 and #11).