///exercise: Xenon gas
  //
  G4Element* Xe = new G4Element("Xenon","Xe", z=54., a= 131.29*g/mole);
  
  //XenonGas1
  G4double temperature1 = 293.15*kelvin;
  G4double pressure1    = 1*atmosphere;
  G4double density1     = 5.887*mg/cm3;
  G4Material* matXe1 =
  new G4Material("matXenon1",density1, ncomponents=1,
                 kStateGas,temperature1, pressure1);
  matXe1->AddElement(Xe, natoms=1);
  
   //XenonGas2
  G4double temperature2 = 293.15*kelvin;
  G4double pressure2    = 48*atmosphere;
  G4double density2     = density1*(pressure2/pressure1)*(temperature1/temperature2);
  G4Material* matXe2 =
  new G4Material("matXenon2",density2, ncomponents=1,
                 kStateGas,temperature2, pressure2);
  matXe2->AddElement(Xe, natoms=1);