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Forum: Space Applications
Re: Question Unexpected results for fluence and TID using Spenvis/GRAS (Svetlana Shasharina)
Re: More Re: Unexpected results for fluence and TID using Spenvis/GRAS (Roger Byrd)
Date: 09 Apr, 2016
From: Svetlana Shasharina <Svetlana Shasharina>

This line in GRAS is important:

/gras/analysis/setSourceFluenceType CURRENT/FLUX

Spenvis defaults it to

/gras/analysis/setSourceFluenceType FLUX.

GRAS results in FLUX are 4 times larger than in CURRENT (both for TID 
and fluece).

Using CURRENT gives TID consistent with G4, but the fluence is still 4 
times lower than the one that I expect from comparing with integral 
fluence given as input for simulation.

Using FLUX results in TID 4 times smaller than from G4 and in fluence 16 
smaller than expected.


On 4/2/16 10:03 AM, Roger Byrd wrote:
> *** Discussion title: Space Applications
> I have tested a normalization approach that seems to help with the
> various GRANT-based MULASSIS and GRAS routines.
> In many space applications with omnidirectional or plane-parallel
> sources, the generated fluence is uniform throughout the problem
> geometry in the absence of particle interactions -- that is, with
> virtual geantinos or with the VOID entry used in the MCNP program.
> For SPENVIS, the equivalent approach replaces the shielding materials
> with Vacuum and then analyzes (tallies) the resulting fluences
> throughout the geometry, whether using MULASSIS, GRAS/MULASSIS, or
> GRAS/GDML. One often finds that a generating source that was expected to
> produce a unit fluence in fact produces two or four times that result.
> One can then either renormalize the doses by the observed factor or
> adjust the input source fluence to produce an observed result of unity.
> This approach has worked with both MULASSIS and GRAS, using parallel
> beams or omnidirectional sources, with both slab and shell shielding.
> -------------------------------------------------------------
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