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Forum: Space Applications
Re: None Untitled (Andres)
Date: 06 Feb, 2006
From: Hugh Evans <Hugh Evans>

Hello Andres,


Andres <Andres.Russu@uv.es> wrote on 06/02/2006 10:34:35:

> *** Discussion title: Space Applications
> Email replies to space_app-g4hn@slac.stanford.edu must include:
>   In-Reply-To: <"/space_app/13"@geant4-hn.slac.stanford.edu>
>   Subject: ...change this to be about your reply.
>
> I have two questions about spacecraft geant simulation.
>
> 1.- The number of particles. I am using gps and sphere source with
> spenvis histogram but I am not sure how many particles per second I have
> to simulate.

The spenvis macro files are generated for the mission fluence over the period
you specified on the orbit definition page. Thus the results from a mulassis
run on SPENVIS will give the quantities (dose, etc) for the total mission
period.

If it is the space station that you're simulating, and only looking at the
contribution from trapped protons or trapped electrons, then you should be
able to divide the results you get by the mission duration in seconds to get
the results per second as a mission average quantity. Look for the
"/analysis/normalise" macro command in the SPENVIS file, that gives the scale
factor to convert from the simulation results to environmental results.
(NOTE: spenvis/mulassis automatically accounts internally for the surface
area of the particle source sphere. If you're not running mulassis, then
you'll have to further multiply the normalisation factor by the surface area
of your sphere source).

If you're using solar protons, then it's more complicated due to the
stochastic nature of the events. You'll have to pick some events and see what
the activation is on an event by event basis (bearing in mind that you'll
have to include the geomagnetic shielding of the event).

If you mean the number of events that you need to simulate, then keep
increasing the number until your statistics are acceptable. ;-)

>
> 2.- Long term radiation. I would like to simulate long term secondary
> particles coming from the desactivation of the ISS materials. Do you
> have any idea about how to do this?

For the long term radiation, I'd investigate the time constant of the decay
that generates the long term secondary particles. If this is less than an
orbital period, then you'll need to perform your analysis for a per orbit
simulation, e.g. a trajectory crossing the SAA or the polar horns, rather
than a mission average. If, however, the decay constant is greater than a
day, then you should be able to get by using the mission average values. The
models of the trapped radiation belts are long term averages, which
simplifies the analysis - you don't have to worry about short term
(weekly/monthly) variations (if you want to, then you'll have to go to data
sets of in-situ measurements). Then, it's a matter of running your simulation
for a representative day of the mission, and calculating the activitation
from that day. From this you can then determine the long term secondary
radiation.

Regards,
Hugh

-----
H. Evans
ESA/ESTEC/TEC-EES
Postbus 299
2200 AG Noordwijk
The Netherlands

Phone:+31 (0)71 565-5109
Fax:     +31 (0)71 565-4999



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