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

  <!-- Reflective box -->
  <surface id="1" type="x-plane" coeffs="-5" boundary="reflective"/>
  <surface id="2" type="x-plane" coeffs="5" boundary="reflective"/>
  <surface id="3" type="y-plane" coeffs="-5" boundary="reflective"/>
  <surface id="4" type="y-plane" coeffs="5" boundary="reflective"/>
  <surface id="5" type="z-plane" coeffs="-5" boundary="reflective"/>
  <surface id="6" type="z-plane" coeffs="5" boundary="reflective"/>
  <cell id="1" material="1" region="1 -2 3 -4 5 -6" />
    
</geometry>
