<?xml version='1.0' encoding='utf-8'?>
<geometry>
  <cell id="1" material="void" region="-1" universe="1" />
  <cell id="2" material="void" region="1 -2" universe="1" />
  <cell id="3" material="void" region="2 -3" universe="1" />
  <cell id="4" material="void" region="3 -4" universe="1" />
  <surface coeffs="0.0 0.0 0.0 1.0" id="1" type="sphere" />
  <surface coeffs="0.0 0.0 0.0 2.0" id="2" type="sphere" />
  <surface coeffs="0.0 0.0 0.0 2.5" id="3" type="sphere" />
  <surface boundary="vacuum" coeffs="0.0 0.0 0.0 4.0" id="4" type="sphere" />
</geometry>
<?xml version='1.0' encoding='utf-8'?>
<materials>
</materials>
<?xml version='1.0' encoding='utf-8'?>
<settings>
  <run_mode>fixed source</run_mode>
  <particles>1000</particles>
  <batches>10</batches>
  <source strength="1.0">
    <space type="point">
      <parameters>0 0 0</parameters>
    </space>
  </source>
  <surf_source_write>
    <surface_ids>1</surface_ids>
    <max_particles>1000</max_particles>
  </surf_source_write>
  <seed>1</seed>
</settings>
<?xml version='1.0' encoding='utf-8'?>
<tallies>
  <filter id="1" type="cell">
    <bins>3</bins>
  </filter>
  <tally id="1">
    <filters>1</filters>
    <scores>flux</scores>
  </tally>
</tallies>
