Dose calculation - example radioprotection

I have a box shape target (aluminum) in front of a water detector. I am trying to simulate GCR spectrum with gps and evaluate the dose. I cannot use spenvis since i am working with mixtures, but I would like to do a similar type of analysis. For this purpose, i have modified the exampleB1 using the general particle source, and I am using macro file similar to that of the radioprotection example.
In the radioprotection example a sphere is used as the source:

type and distribution of beam

/gps/pos/type Surface
/gps/pos/shape Sphere

Set angular distribution

/gps/ang/type cos
/gps/ang/mintheta 0. deg
/gps/ang/maxtheta 0.003 deg
/gps/ang/minphi 0. deg
/gps/ang/maxphi 360. deg

  1. what is the meaning of minphi and maxphi?
  2. How is the normalization factor for the dose evaluation calculated If I consider mintheta = 0 and maxtheta=90? If I am not wrong, it should be Fmax (integral fluence at maximum energy)- Fmin (integral fluence at minimum energy) *piR^2, all divided by N = number of particles shot, or should I someway consider the mintheta and maxtheta values in the evaluation of the normalization factor?
  1. The primary is generated from a point P of the surface of the sphere. The primary particle direction is expressed in terms of theta and phi. Phi is the angle of the direction in the plane tangent to the sphere in P.

  2. In the calculation of the dose you should take into account the fact that the generation of the primaries is biased in terms of direction (theta max)
    I suggest to look at this presentation where these concepts are explained:

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Thank you very much.
I read the pdf by Dr. Santin, but I don’t understand the phi (flux) term of the normalization. According to the spenvis manual it should be the difference between the flux at minimum energy minus the flux at maximum energy of my spectrum. If so, is it referred to the differential flux (that for the radio protection example would be 202.26-0.000060364) or to the integral flux?

I think you can decide either to fix a phi angle in your primary or just not specify and then you normalize the generation of primaries afterwards.
I personally fixed only theta min and max in order to have a cone of primaries particles hitting the target, to fasten up the simulation and not losing time shooting particle 4Pi that won’t hit the target. The cone is generated for each random point on a sphere surrounding the target (this is set in the so you can avoid to fix the phi angle in the gps).
The output (number of events of energy deposition) has been normalized all over 4Pi to mimic the realistic isotropic exposition in space. For doing that I used the formula form G. Santin.
The phi flux term in the formula is the integrated flux of incident particles simulated
by SPENVIS, on the theta angle of interest, that you shot in your simulation.
If it is not clear, I can give you a few references.

Hi there! I actually stumbled across this thread as I am doing something similar. I was wondering if you could possibly send me the references that you’re talking about. Also, when you normalize, what are the units of the Ns term? I’m assuming just particle fluence but…

The units for Ns are simply counts, as it is the number of events simulated.
You can have a look at this published paper: S. Peracchi, et al., “Modelling of the Silicon-On-Insulator microdosimeter response within the International Space Station for astronauts’ radiation protection,” Radiation Measurements, vol. 128, September 2019, Art. no. 106182.
And also at the presentation link that Susanna attached in the first reply above.

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Ok thank you! I had a look through the power point pretty closely. So I have two Gamma spectrums (0.7MeV to 6 MeV for the first, and 0.7 MeV to 26.5 MeV for the second) and two different environmental geometries. The gamma spectra were measured using an NaI scintillator which I know the dimensions of. I’m just wondering how I go from just a regular old count rate, to an energy integrated one? I get that I have to integrate it over the whole spectrum, but I just am not using SPENVIS and im wondering if that will affect anything.

I personally used SPENVIS only to generate the input flux for the GEANT4 simulation.
So I think that you can simply consider our count rate and convert it to flux (integrated or differential) accordingly to your geometry specs.

THank you again! So by geometry specs you’re talking my detector geometry or my source geometry? Sorry just wanna make this super clear! I already have the simulation itself essentially done I just need to normalize my results now.

You’re welcome !
I meant your source geometry.
I do not know your source geometry, but if you want to have a 4Pi or 2Pi isotropic exposure as occurring is space, you need to normalize the counts you obtained from your geometry to the counts you would have got from a sphere (particles generated from each point on the sphere surface, and propagating inwards, towards the center where hypothetically you have your detector, for example).