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

  <surface id="1" type="sphere" coeffs="0 0 0 10" boundary="vacuum"/>
  <surface id="2" type="z-plane" coeffs="-100" />
  <surface id="3" type="z-plane" coeffs="100" />

  <cell id="1" fill="2" region="-1" />
  <cell id="2" universe="2" material="1" region="2 -3" />

</geometry>
