[Gate-users] Abslength issue

[Sean Jones]

I am running a simulation of a phoswich detector.  In order to
determine light capture efficiency of the system, I am looking to
determine from the ASCII file output, the number of photons created
vs. the number generated.

I have spent much time and attention on the simulation.  However, I
seem to have run across and interesting observation that I believe may
be a bug.  Unfortunately, this is a large speed bump I must overcome
in order to move ahead with this research.

In running simulations I have input a value of 250 (units of cm) for
the property abslength in the materials.xml file.  When doing so I can
count optical photons that strike the photocathode.  When I run the
same simulation, and switch the value from 250 (with units of cm) to
2.5 (units of m), ALL of the optical photons generated are absorbed
before hitting the photocathode.  Each simulation generates a similar
number of optical photons, and in theory the two values should be
identical and yield similar results.  I've switched back and forth
various times, and it seems that the input depends on the magnitude of
the number input and disregards the unit used.  As such, I believe
I've encountered a bug in the GATE code and how it implements the unit
value for abslength property, or perhaps I've missed something
important between the two manuals.

Furthermore, I am uncertain of the definition of the abslength value
that must be used for optical materials.  I am aware that these are
empirical values:
Bulk absorption (discussed in the GEANT4 manual), and Bulk attenuation
(I believe reduces light by a factor of e^-1).  I have these two
values for only one of my materials from our detector manufacturer.
However, if you have any input as to what those values actually mean,
which one must be implemented in the GATE framework (specifically what
units the input seems to be stuck to, if it is somehow unchageable as
a bug), and where
one could find a list of this empirical data for various optical and
scintillation materials, I would be most appreciative.

Thank you for your time.

-- 
Sean Jones
Graduate Teaching Assistant
Department of Nuclear Engineering and Radiation Health Physics
Oregon State University
130 Radiation Center
Corvallis, Oregon 97331
Office C-128
Phone:541-737-2017