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

  <!-- Sphere with no boundary condition -->
  <surface id="1" type="sphere" coeffs="0.0 0.0 0.0 80.0" />
  <surface id="2" type="sphere" coeffs="0.0 0.0 0.0 10000.0" boundary="vacuum" />
  <cell id="1" material="1" region="-1" />

</geometry>
