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<!--    1st version created:  Katsuya Amako, Dec-2006         -->
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<!-- ********************* QandA Section ******************** -->
<section id="qanda.PhysicsCuts">
<title>
Physics and cuts
</title>

<qandaset defaultlabel="qanda">


<!-- ******* QandA Entry ******** -->
<qandaentry  id="qanda.PhysicsCuts.HowProdCuts">

<question><para>
  How do production cuts (in range) work in Geant4 ? Are they also used 
  in tracking ? If a particle has an energy lower than the converted cut 
  in energy for the given material and the distance to the next boundary 
  is smaller than the cut in range, is the particle killed ? 
</para></question>

<answer><para>
  Geant4 does <emphasis role="bold">NOT</emphasis> have a "tracking cut". 
  The toolkit's default behaviour is to track particles down to zero range 
  (i.e. zero energy). Of course, it is possible for the user to create and 
  register a process that kills particles below a certain energy or range; 
  this is however <emphasis role="bold">NOT</emphasis> provided by default 
  in Geant4. So there's <emphasis role="bold">NO</emphasis> "tracking cut".
  For example, suppose a particle that is nearing zero energy will at some 
  point be proposed by its Ionisation process to undergo one final step, 
  from its current energy down to zero energy. This is still only a 
  proposal. If during this step the particle crosses a boundary, then the 
  transportation will limit the step at a length smaller than the 
  Ionisation -- so the particle will still see and cross the relevant 
  boundary, and another step will occur on the other side of that boundary.
  In summary the "production threshold" range and its equivalent in energy 
  are not utilised as a "tracking cut". A particle is not abandoned by 
  Geant4 below a certain range/energy unless the user registers a process 
  to do this by him/her-self.
</para></answer>

</qandaentry>


</qandaset>
</section>
