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Forum: Space Applications
Re: None Untitled (Andres)
Re: None Re: Untitled (Hugh Evans)
Date: 22 Feb, 2006
From: <Andres.Russu@uv.es>

Hello Hugh,



> 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).

From the MULASSIS Software Users Manual I have learnt about the 
Normalize factor. Now, I am multiplying each bin of the histogram for 
the normalisation factor.

 
> 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 my sphere is 5 m radius, I think I don't have to take into account 
the geomagmnetic shielding effects (they will be despreciable), Do I?
 
> If you mean the number of events that you need to simulate, then keep
> increasing the number until your statistics are acceptable. ;-)
> 

I am increasing the number until the spenvis fluence is reached. This 
point is in 7e3 particles(eg) but if I want to get the corrected 
fluence it is reached in 7e15 particles (eg) as my normalization 
factor is 1e12 (eg). So, Which is the fluence that I must reach to get 
good stadistics? 

> >
> > 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
> 

The second point will come later.

Thank you in advance,
Andres

*****************************************
Andres Russu
Andres.Russu@uv.es
Astronomy and Space Science Group (GACE)
Ph: 0034 96 354 36 79
Fax: 0034 96 354 36 77
*****************************************




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