diff --git a/bind/bindings.cpp b/bind/bindings.cpp
index 63d5907..a38bbb3 100644
--- a/bind/bindings.cpp
+++ b/bind/bindings.cpp
@@ -29,7 +29,8 @@ void makeG4System(M &m, std::string name)
 {
     py::class_<G4System>(m, name.data()).def(py::init())
     .def("init", &G4System::init, py::arg("cw")).def("run_visualize", &G4System::run_visualize, py::arg("partSpecies"), py::arg("minEnergy_GeV"), py::arg("maxEnergy_GeV"))
-    .def("run_gui", &G4System::run_gui).def("run_batch", &G4System::run_batch, py::arg("nEvents"), py::arg("partSpecies"), py::arg("minEnergy_GeV"), py::arg("maxEnergy_GeV"))
+    .def("run_gui", &G4System::run_gui)
+    .def("run_batch", &G4System::run_batch, py::arg("nEvents"), py::arg("partSpecies"), py::arg("minEnergy_GeV"), py::arg("maxEnergy_GeV"), py::arg("filename")="_1234567890_Hits.root")
     .def("applyUICommand", &G4System::applyUICommand, py::arg("command"))
     .def("displayEvent", &G4System::displayEvent)
    // .def("printMaterial", &G4System::printMaterial, py::arg("name"))
diff --git a/include/ActionInitialization.hh b/include/ActionInitialization.hh
index 0ceda01..0812553 100644
--- a/include/ActionInitialization.hh
+++ b/include/ActionInitialization.hh
@@ -32,6 +32,7 @@
 
 #include "G4VUserActionInitialization.hh"
 #include "PrimaryGeneratorAction.hh"
+#include "RunAction.hh"
 
 namespace B4
 {
@@ -66,12 +67,21 @@ class ActionInitialization : public G4VUserActionInitialization
       fDetConstruction = det;
     }
 
+    void setFileName(G4String fileName){
+      this->filename = fileName;
+      if(runact!=nullptr){
+          runact -> setFileName(fileName);
+      }
+    }
+
   private:
     B4::DetectorConstruction* fDetConstruction = nullptr;
     mutable B4::PrimaryGeneratorAction * gen = nullptr;
+    mutable B4::RunAction * runact = nullptr;
     G4double minEnergy=1000;
     G4double maxEnergy=1000;
     G4String partSpecies="e-";
+    G4String filename="";
 };
 
 }
diff --git a/include/G4System.hh b/include/G4System.hh
index d9274fe..7e118b8 100644
--- a/include/G4System.hh
+++ b/include/G4System.hh
@@ -19,6 +19,7 @@
 #include "Randomize.hh"
 
 class G4System{
+  friend class GeometryDescriptor;
 public:
 
 G4System(bool Gui=false):gui(Gui){};
@@ -37,7 +38,8 @@ void init(GeometryDescriptor &cw);
 void run_visualize(const std::string& partSpecies, double minEnergy_GeV, double maxEnergy_GeV);
 //runs the whole gui if available
 void run_gui();
-void run_batch(int nEvents, const std::string& partSpecies, double minEnergy_GeV, double maxEnergy_GeV);
+void run_batch(int nEvents, const std::string& partSpecies, double minEnergy_GeV, 
+           double maxEnergy_GeV, std::string filename="_1234567890_Hits.root");
 
 void applyUICommand(const std::string& command){
     check();
diff --git a/include/GeometryDescriptor.hh b/include/GeometryDescriptor.hh
index d86aba7..619ff42 100644
--- a/include/GeometryDescriptor.hh
+++ b/include/GeometryDescriptor.hh
@@ -7,7 +7,7 @@
 #include <string>
 //#include "G4VPhysicalVolume.hh"
 class G4VPhysicalVolume;
-
+class G4System;
 
 class Sensor{
 public:
@@ -90,7 +90,7 @@ class GeometryDescriptor{
 
 public:
   GeometryDescriptor(double xy_width=50);
-  ~GeometryDescriptor() {};
+  ~GeometryDescriptor();
 
   void addLayer(double thickness_cm, std::string material, bool isActive=true, int nx=1, int ny=-1);
   
@@ -134,10 +134,13 @@ public:
         }
     }
 
-
+    void setG4System(G4System* g4system){
+        this->g4system = g4system;
+    }
 private:
     double xywidth;
     std::vector<Layer> layers;
+    G4System * g4system;
 };
 
 #endif
\ No newline at end of file
diff --git a/include/RunAction.hh b/include/RunAction.hh
index 7324984..6c89fc2 100644
--- a/include/RunAction.hh
+++ b/include/RunAction.hh
@@ -65,6 +65,10 @@ class RunAction : public G4UserRunAction
     void BeginOfRunAction(const G4Run*) override;
     void   EndOfRunAction(const G4Run*) override;
 
+    void setFileName(G4String name){
+      filename = name;
+    }
+
 //now this is dumb but the way this is setup it has to be done like this
 
 //yeah mutable fine whatever
@@ -78,6 +82,8 @@ class RunAction : public G4UserRunAction
   mutable std::vector<int> hitLayer;
   mutable std::vector<int> hitCopyNumber;
 
+  mutable G4String filename;
+
 };
 
 }
diff --git a/src/ActionInitialization.cc b/src/ActionInitialization.cc
index e025696..d862832 100644
--- a/src/ActionInitialization.cc
+++ b/src/ActionInitialization.cc
@@ -62,7 +62,8 @@ void ActionInitialization::Build() const
   gen->setMaxPartEnergy(maxEnergy);
   gen->setPartSpecies(partSpecies);
   SetUserAction(gen);
-  auto runact = new RunAction;
+  runact = new RunAction;
+  runact -> setFileName(filename);
   SetUserAction(runact);
   auto eventAction = new EventAction;
   eventAction->setRunAction(runact);
diff --git a/src/G4System.cc b/src/G4System.cc
index a24ed72..9bd61b6 100644
--- a/src/G4System.cc
+++ b/src/G4System.cc
@@ -19,6 +19,7 @@ void G4System::init(GeometryDescriptor &CW){
     assigned_cw->unAssign();
   }
   assigned_cw = &CW;
+  CW.setG4System(this);//link both ways
 
   char* argv[]={(char*)"dummy"};
 
@@ -156,7 +157,8 @@ void G4System::run_gui(){
   }
 }
 
-void G4System::run_batch(int nEvents,const std::string& partSpecies, double minEnergy, double maxEnergy){
+void G4System::run_batch(int nEvents,const std::string& partSpecies, double minEnergy, 
+double maxEnergy, std::string filename){
   check();
 
 
@@ -165,6 +167,7 @@ void G4System::run_batch(int nEvents,const std::string& partSpecies, double minE
     UImanager->ApplyCommand("/run/initialize");
     UImanager->ApplyCommand("/vis/disable");
     actionInitialization->setGeneratorProperties(minEnergy, maxEnergy, partSpec);
+    actionInitialization->setFileName(filename);
     runManager->BeamOn(nEvents);
 }
 
diff --git a/src/GeometryDescriptor.cc b/src/GeometryDescriptor.cc
index 6f9bd82..ba63616 100644
--- a/src/GeometryDescriptor.cc
+++ b/src/GeometryDescriptor.cc
@@ -2,6 +2,7 @@
 
 #include "GeometryDescriptor.hh"
 #include "G4VPhysicalVolume.hh"
+#include "G4System.hh"
 
 Layer::Layer(){
     thickness = 0;
@@ -40,6 +41,13 @@ GeometryDescriptor::GeometryDescriptor(double xy_width){
     xywidth = xy_width;
 }
 
+GeometryDescriptor::~GeometryDescriptor() {
+    if(g4system != nullptr){
+        if(this == g4system->assigned_cw){ //unassign
+            g4system->assigned_cw = nullptr;}
+    }
+};
+
 void GeometryDescriptor::addLayer(double thickness, std::string material, bool isActive, int nx, int ny){
     if(ny<0){
         ny = nx;
diff --git a/src/RunAction.cc b/src/RunAction.cc
index 85b7360..160f566 100644
--- a/src/RunAction.cc
+++ b/src/RunAction.cc
@@ -96,12 +96,11 @@ void RunAction::BeginOfRunAction(const G4Run* /*run*/)
 
   // Open an output file
   //
-  G4String fileName = "_1234567890_Hits.root";
   // Other supported output types:
   // G4String fileName = "B4.csv";
   // G4String fileName = "B4.hdf5";
   // G4String fileName = "B4.xml";
-  analysisManager->OpenFile(fileName);
+  analysisManager->OpenFile(filename);
   G4cout << "Using " << analysisManager->GetType() << G4endl;
 }