Problem 304

Summary:	questions about operation of particle cuts, also low energy question
Product:	Geant4	Reporter:	hopkins
Component:	processes/electromagnetic/lowenergy	Assignee:	Maria.Grazia.Pia
Status:	RESOLVED FIXED
Severity:	normal
Priority:	P2
Version:	1.0
Hardware:	Other
OS:	Windows

Description hopkins 2001-09-26 14:57:39 CEST

I have two questions rather than "problems" to report.

1.  I have been under the impression that a particle cut value as a value
against which a  mean free path for the current particle/environment was
compared - a mean free path less than the cut value caused the energy to be
deposited at the current location.  According to this, when I increase the cut
value, the processes should continue.  I am looking at a simple case of energy
deposition with a single energy (e.g. 50 keV) photon in a single material (e.g.
CsI). When I increase the cut for photons and electrons from 0.01mm to 0.10 mm,
I see more dispersion of energy spatially - implying to me that implies the
energy loss processes were allowed to extend further spatially.  I would have
expected the opposite, if my original interpretation were correct.  In effect,
when you increase the cut value, you extend the interactions to a greater
spatial distribution.  Comments?

2.  I am interested in very low energy events (<10 keV photons and electrons).
I know the low energy package was added to Geant4 - I note the message about
handling electons down to 250 eV in energy. Do you have validation to support
the accuracy of the modeling down to energies in that region, including the
loss of energy/stopping ranges of electrons in the 0.25-5 keV range, and is
there some way to handle electrons below 250 eV in energy?

Thanks for help.
Forrest Hopkins

Comment 1 kurasige 2001-09-27 19:44:59 CEST

Dear Forrest,

  Here is my answer to your first question.

  In Geant4, the cut associated with the particle is a (recommended) production
threshold of secondary particles. Cut value is given in length by users but it
can be converted to energy for each material. It means that particles which
energy is less than the cut are not produced by processes.
  For example, number of delta rays which are produced along the charged track
decreases by setting higher range cut value because low energy gamma below
energy cut value are suppressed.

  You can see the detail of "cut in Geant4" in
  Geant4 User's Guide For Application Developers
   3.18 Production Threshold versus Tracking Cut

Regards,
                              Hisaya

Comment 2 pia 2001-09-28 03:50:59 CEST

Documentation about the validation of Geant4 Low Energy Electromagnetic package
can be found on the web site of the project, http://www.ge.infn.it/geant4/lowE/
In particular, one can follow the "Results" link on that page to access a
collection of validation plots. Other results are also contained in the various
papers accessible from the "Publications" link.
Concerning extensions below 250 eV, the Geant4 Low Energy Electromagnetic
Working Group has plans to further extend the coverage below the current
threshold. The time scale is currently under evaluation.

Best regards,
Maria Grazia Pia