The energy spectrum selection for the mission based environment depends on which SPENVIS radiation model has run before. If the Trapped proton and electron fluxes, the Solar particle mission fluences or the Galactic cosmic ray (GCR) fluxes models have run then the options are averager trapped particle fluence, solar particle fluence and GCR particle fluence respectively.
Next, the user then to give the number of incident particles he wants to simulate in the Monte-Carlo run. As the total time for the run is limited, this number should be chosen as small as possible but large enough to provide statistically meaningful results. As a guideline, users should first make a run with a limited number of incident particles. When the results seem to make sense, a new run with more particles can be made to improve the statistics.
Warning: The particle track visualisation will be disabled when the number of particle is greater than 100!
The type of incident particles can be selected with the menu electronpositronproton neutronalphaiongamma geantino. Only when selecting the ion option, additional inputs are required. These consist of:
Note that the type of incident particles is related to the environment selection. Therefore, when a mission based environment is chosen only electron (trapped particles), proton (trapped particles, long-term solar particles) or ion (GCR particles) are available.
Note that it is assumed that all of the particle spectra are omnidirectional, or have been integrated over 4π, i.e. there are no units for sr-1. The particle spectra can be either flux or fluence spectra. For this reason, the unit (s-1) is placed between brackets. The units for other terms depend on the angular distribution (see below).
As the spectra obtained from the trapped particle, long-term solar particles and GCRs models, as well as the user-defined spectrum consist of pointwise data, these can be interpolated for other energies using several interpolation methods. The methods available are: linearpower-law exponentialcubic spline.
The energy E is expressed in MeV, and the default values for A and B are 1.0 and 0.0 respectively. The minimum and the maximum energy range must also be specified (these values default to 0.0 MeV and 100.0 MeV).
In this case, the exponent alpha has to be defined by the user (the default value is -1.0). The constant A has the same function as the source strength parameter defined above. In this case, the minimum and maximum energy to be considered have to be defined as well (the default values being 1.0 MeV and 100.0 MeV respectively).
The exponent E0 has to be defined (the default value is 1.0 MeV). As in the previous case, the value of the constant A has the same function as the source strength parameter defined above. Again, the minimum and maximum energy to consider in the spectrum have to be given (the default values being 0.0 MeV and 100.0 MeV respectively).
For a mission based environment the omnidirectional angular distribution is recommended.
The first normalisation factor n1 is related to the number of particles in the energy range for the different flux/fluence spectra. In the following table the formulas of n1 for all the possible types of incident particle spectra in SPENVIS are provided:
where I(E0) is the fluence/(flux) intensity and F denotes the integral fluence/(flux). For the User defined or SPENVIS generated spectrum, the normalisation factor is calculated by simply subtracting the fluence/flux at the maximum energy in the spectrum from the fluence/flux at the minimum energy.
Next, the normalisation factors n2 related to the angular distribution are provided:
Note that the one over 4π factor in the above formulas is because of the assumption that all of the particle spectra are omnidirectional, or have been integrated over 4π.
The two normalisation factors n1 and n2 are recorded as aliases in the generated macro file namely NORM_FACTOR_SPECTRUM and NORM_FACTOR_ANGULAR respectively.
Finally, note that SPENVIS is taking into account any unit transformation necessary in order to ensure that the normalisation factor is calculated in terms of particles per cm -2.