Gun.py: when setting gun.energy, set both min and max

src/dd4pod/python/npsim/DDSim/Helper/Gun.py

@@ -113,7 +113,9 @@ class Gun(ConfigHelper):
   def setOptions(self, ddg4Gun):
     """set the starting properties of the DDG4 particle gun"""
     try:
-      ddg4Gun.energy = self.energy
+      ddg4Gun.energy = self.energy # ddg4Gun.energy actually sets momentum
+      ddg4Gun.MomentumMin = self.energy
+      ddg4Gun.MomentumMax = self.energy
       ddg4Gun.particle = self.particle
       ddg4Gun.multiplicity = self.multiplicity
       ddg4Gun.position = self.position