Use of USRBIN and intensity plotting for various x-ray energy

Scoring
9

Dear @uchow,

I looked at your files and I believe your results make sense. Indeed, a difference in attenuation is to be expected, but your method does not allow for a proper visualisation. A combination of two factors explains what you reported:

  1. Your materials are heavy or very heavy (Cu, Pb, W and U). As a result, only a small fraction of the X-rays make it through them. This makes difficult to observe differences in attenuation.

  2. It gets worse because of your spherical regions and the projection used to get the attenuation profile you shared above. Most probably your projection is not restricted to those bins along the centre of your spheres, but you are adding photons that did not pass through the spheres (but around them) to the tiny quantity that manages to go through them (see previous comment). Therefore, changes in that tiny quantity are difficult to visualise. Better statistics and logarithmic scale may help, but the solution would be to define a proper projection and/or change for a better setup.

In order to check by yourself, you can do the following:

  1. Try with lighter materials (e.g. water): the difference in attenuation for both energies will be much clearer.
  2. Restrict your projection to those bins across the centre of your spheres. Consider using cubes or similar instead of spheres so you can make a cleaner projection, at least until you fully understand the issue.

Finally, few comments about your inputs that may be of help:

  • Be careful with the ASSIGNMA card. I have seen one with an empty “Reg” field. By default, FLUKA will assign that material to the 2nd region of your geometry, VOID in your case, which would mess up your calculation ( WHAT(2) explanation in ASSIGNMAt | FLUKA).
  • When using a source routine, select a beam energy in the BEAM card above the maximum energy you will use in the routine (note 3 in SOURCE | FLUKA).
  • You are using a huge number of bins in your USRBINs. This will only consume memory and make things slower. Consider reducing them according to your needs.
  • Your beam definition is suboptimal. Using a fully isotropic source, you are spending a considerable amount of time sampling, simulating and scoring photons that will never reach your spheres. To avoid this, you can restrict the photon sampling to those directed towards your area of interest.

Let us know in case the problem persists.

Kind regards,
Francisco