<?xml version="1.0"?>
<materials>

  <!-- Definition of materials -->
  <material id="1">
    <density value="4.5" units="g/cc" />
    <nuclide name="U235" ao="1.0" />
  </material>

  <material id="2">
    <density value="1.0" units="g/cc" />
    <nuclide name="H1"  ao="2.0" />
    <nuclide name="O16" ao="1.0" />
  </material>

</materials>
