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Forum: Space Applications
Re: Question Unexpected results for fluence and TID using Spenvis/GRAS (Svetlana Shasharina)
Date: 08 Mar, 2016
From: Svetlana Shasharina <Svetlana Shasharina>

One more data point, when I switch from FLUX to CURRENT normalization, 
the TID becomes 4 times larger, while fluences become 4 times
smaller.

Sveta

On 3/8/16 11:07 AM, Svetlana Shasharina wrote:
> *** Discussion title: Space Applications
>
> I did the following calculations using Spenvis/GRAS(gdml):
>
> 1. Independent runs for two vacuum spheres with r = 19cm and r = 15 cm.
> Source: Monoenergetic (100MeV) electrons with fluence 100 (1/cm^2 s),
> sphere with r = 20cm.
>
> SPENVIS calculated fluences 28390 and 17644 for the first and the second
> spheres. The ratio of fluences/surface_area is constant for these cases
> (6.24 and 6.26) and is very close to 2pi :-) but is very different from
> the incident fluence (100).
>
> First confusion: I thought the calculated fluence is normalized to the
> target's areas. But looks like it is not. Second confusion: after
> dividing by the surface areas I still have a number very different to
> the incident environment number (100).
>
> Maybe I do not understand what the incident fluence really mean? How do
> I get a number that would relate to it?
>
> 2. Ta sphere r = 15cm, calculating TID in MeV with the source described.
> I get 1.6564e+06MeV/s.
>
> If all e were to absorb, I would expect 100(1/cm^2 s)*100MeV*SurfaceArea
> = 1e+4 MeV/s *2826cm^2 = 2.8e+7 MeV/s.
>
> So about 1/16 of the electrons gets absorbed, I guess? If I change
> normalization to CURRENT instead of FLUX, I will get 1/4 difference, I
> assume. Still a big difference. Any intuitive reaction to this
> difference?
>
> Best regards, Sveta
>
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