bug solved

include/B1SD.hh

@@ -22,7 +22,8 @@ public:
   G4bool ProcessHits(G4Step* step, G4TouchableHistory* ROhist);
 
   void Initialize(G4HCofThisEvent* HCE);
-  //void EndOfEvent(G4HCofThisEvent* HCE);
+
+  void EndOfEvent(G4HCofThisEvent* HCE);
 
 private:
   B1HitsCollection* hitCollection;

src/B1SD.cc

@@ -54,3 +54,7 @@ void B1SD::Initialize(G4HCofThisEvent* HCE) {
   if (HCID < 0) HCID = GetCollectionID(0);
   HCE->AddHitsCollection(HCID, hitCollection);
 }
+
+void B1SD::EndOfEvent(G4HCofThisEvent* HCE) {
+  track_id = 0;
+}