diff --git a/src/SystemBuilder.cc b/src/SystemBuilder.cc
new file mode 100644
index 0000000..6e8cf91
--- /dev/null
+++ b/src/SystemBuilder.cc
@@ -0,0 +1,66 @@
+
+#include "SystemBuilder.hh"
+
+void SystemBuilder::init(ConstructionWrapper &CW, bool gui){
+
+  char* argv[]={(char*)"dummy"};
+
+  // Construct the default run manager
+  //
+  runManager =
+    G4RunManagerFactory::CreateRunManager(G4RunManagerType::Default);
+  runManager->SetNumberOfThreads(1);
+
+  G4String session;
+  ui = nullptr;
+  if ( gui ) {
+    ui = new G4UIExecutive((int)1, argv, session);
+  }
+
+  // Set mandatory initialization classes
+  //
+  detConstruction = new B4::DetectorConstruction(&CW);
+
+  runManager->SetUserInitialization(detConstruction);
+
+  auto physicsList = new FTFP_BERT;
+  runManager->SetUserInitialization(physicsList);
+
+  actionInitialization = new B4a::ActionInitialization(detConstruction);
+  runManager->SetUserInitialization(actionInitialization);
+
+  actionInitialization->setGeneratorProperties(100, 10000, "e-");
+
+  // Initialize visualization
+  //
+  visManager = new G4VisExecutive;
+  // G4VisExecutive can take a verbosity argument - see /vis/verbose guidance.
+  // G4VisManager* visManager = new G4VisExecutive("Quiet");
+  visManager->Initialize();
+
+  // Get the pointer to the User Interface manager
+  UImanager = G4UImanager::GetUIpointer();
+
+  // Process macro or start UI session
+  //
+}
+
+void SystemBuilder::run_gui(){
+    if(ui == nullptr){
+        throw std::runtime_error("GUI not initialized");
+    }
+    if ( true ) {
+    // interactive mode : define UI session
+    UImanager->ApplyCommand("/control/execute init_vis.mac");
+    if (ui->IsGUI()) {
+      UImanager->ApplyCommand("/control/execute gui.mac");
+    }
+    ui->SessionStart();
+  }
+}
+
+void SystemBuilder::run_batch(int nEvents, std::string partSpecies, double minEnergy, double maxEnergy){
+    actionInitialization->setGeneratorProperties(minEnergy, maxEnergy, partSpecies);
+    UImanager->ApplyCommand("/run/initialize");
+    runManager->BeamOn(nEvents);
+}
\ No newline at end of file