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Hello Hugh, > Hello Andres, > > > Andres <Andres.Russu@uv.es> wrote on 06/02/2006 10:34:35: > > > *** Discussion title: Space Applications > > Email replies to email@example.com 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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