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Forum: Space Applications
Re: Question How to define the flux of particles? (Lee Xuesheng)
Date: 07 Mar, 2006
From: Hugh Evans <Hugh Evans>

Hello Lee,

I would recommend the use of the GPS module in G4 for setting up the primary

To establish a particle source you need to define:
1. the particle source surface - the surface on which the primaries are
2. the angular distribution of the primaries - in space this is usually
3. the energy spectrum

The surface for generating the particle sources is in the most simple, a
sphere that encapsulates the model.

The angular distribution of radiation in space is generally assumed to be
isotropic or omni-directional. There are deviations from this, e.g. at low
altitudes in the South Atlantic Anomaly, during the rising phase of a solar
proton event, or astronomical events such as gamma ray bursts. For radiation
belts, solar proton event and cosmic ray analyses, though, the
omni-directional assumption is usually valid. So, the omni-directional
assumption requires a cosine-law to ensure a correct angular distribution.

If it is radiation belt or solar protons that you are trying to simulate,
then I'd recommend the SPENVIS system ( and it's
mulassis model implementation to generate the energy spectrum GPS macro
calls. Mulassis is a 1D general purpose Geant4 application. It will also
provide you with examples on setting up the GPS parameters.

Then there is the issue of tuning all of the above to ensure each event
produces the data you require. This can be achieved through the biasing of
the angles, energies, etc.


H. Evans
Postbus 299
2200 AG Noordwijk
The Netherlands

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

Lee Xuesheng <> wrote on 07/03/2006 08:54:08:

> *** Discussion title: Space Applications
> Email replies to must include:
>   In-Reply-To: <"/space_app/16">
>   Subject: ...change this to be about your reply.
> When using the geant4 in application for Space Radiation,how can I
> define the flux of particles(e- or gamma)? thanks

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1 None: Re: How to define the flux of particles?   (Andres - 25 Mar, 2006)
3 None: Re: How to define the flux of particles?   (Andres - 25 Mar, 2006)
1 None: Re: How to define the flux of particles?   (Hugh Evans - 27 Mar, 2006)
2 None: Re: How to define the flux of particles?   (Lee Xuesheng - 05 Oct, 2006)
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