diff --git a/NPSimulation/Process/BeamReaction.cc b/NPSimulation/Process/BeamReaction.cc
index 07f42fcf5a43f69cea71093467eedfa6b5a1896a..3ace565b8b17d90d997573c35b3e04c19a6d6c44 100644
--- a/NPSimulation/Process/BeamReaction.cc
+++ b/NPSimulation/Process/BeamReaction.cc
@@ -123,6 +123,11 @@ G4bool NPS::BeamReaction::ModelTrigger(const G4FastTrack& fastTrack) {
   double out   = solid->DistanceToOut(P, -V);
   double ratio = in / (out + in);
 
+  m_Parent_ID = PrimaryTrack->GetParentID();
+  // process reserved to the beam
+  if(m_Parent_ID!=0)
+    return false;
+
   //cout<< "in:"<<in<<std::scientific<<endl;
   //cout<< "ou:"<<out<<std::scientific<<endl;
   //cout<< "ratio:"<<ratio<<std::scientific<<endl;
@@ -137,7 +142,7 @@ G4bool NPS::BeamReaction::ModelTrigger(const G4FastTrack& fastTrack) {
     m_ReactionConditions->Clear();
     shoot = true;
   }
-  else if ((in-m_StepSize) <= 1E-9) { // last step
+  else if (((in-m_StepSize) <= 1E-9) && shoot) { // last step
     //cout<< "LAST"<<endl;
     return true;
   }
@@ -157,7 +162,9 @@ G4bool NPS::BeamReaction::ModelTrigger(const G4FastTrack& fastTrack) {
         } else {
             return false;
         }
-    }else if(m_ReactionType=="TwoBodyReaction"){
+    }
+   
+    else if(m_ReactionType=="TwoBodyReaction"){
         if ( shoot && m_Reaction.IsAllowed(PrimaryTrack->GetKineticEnergy()) ) {
             shoot = false;
             return true;
diff --git a/NPSimulation/Process/BeamReaction.hh b/NPSimulation/Process/BeamReaction.hh
index b77c424d8885112d5152c7b1f2bf32b37999e16d..f5c9a41d28ea2248c90d17cb8aee2cadff4c0fb7 100644
--- a/NPSimulation/Process/BeamReaction.hh
+++ b/NPSimulation/Process/BeamReaction.hh
@@ -52,6 +52,7 @@ namespace NPS{
       double m_PreviousLength;
       bool   m_active;// is the process active
       double m_StepSize;
+      int    m_Parent_ID;
    
    private:
      TReactionConditions* m_ReactionConditions;