Hi Hedi,
since you want to find the 10,000 particles that you declare as source strength, I am making a simple case that I think could help us to understand what openmc did in photon transport.
I am making a simple 3D geometry consisting of a small cube with a size 1x1x1 cm in front of a shield cell, also a cube 1x1x1 on its back. A photon source was placed at -5cm (point source monodirectional monoenergetic) with a source strength of 10,000 as you want.
when all material being used by all cells (cell 01, shield, cube 01, and cube 02) is vacuum or dry air, the photon distribution will look like this
I am using a mesh tally with a size of 1 cm in the x and y directions because I noticed that the 10,000 particle strength was reported at this size, so I think the source strength was defined as 10,000 per cc for this source definition. then, because there is almost no interaction in dry air (vacuum), each mesh in front of the source will report that the particle is 10,000. that’s why the total sum of particles on this mesh tally is 250,000 because there is 25 mesh in front of the source and each reported 10,000 photons. you also noticed that the photon rays are slightly shifted to y negative, that’s because the point source is counted along the mesh on the x-axis. If you move this source to be centered on the x-axis, then your 10,000 particles will be divided into 2, or 5,000 because it was counted in separate mesh bins, but the total photon counted will still be the same ~250,000.
then the 2 cube cells (1x1x1 cm) were used for tallying, so in a vacuum, everything is perfect on 10,000 as you want. if you change the size of the cube, i.e. become 2x2x2 cm, then this cell will count 2x10,000 since it covers 2 cm on the x-axis.
then the plot of photons along the x-axis also shows a 10,000 as you want
and when it comes to changing the 5cm cube of shield cell’s material, let’s say we want it to become water, then the plot will change, and the peak count also drops from 10,000 on cube 01 to around ~1000 on cube 02 on the back of the water shield.
I think there is something interesting about the absorption rate plotted here, but if I activate heating (photon heating), any tally in a vacuum will drop around 0, so yeah, I hope the expert on this topic could help to explain this behavior because I notice this when using vacuum. it is different when I use dry air as shown below.
then this is when we used dry air instead of a vacuum surrounding the shield
and last one is when we use lead which terminates almost all photons counted on cube 02 cell behind the lead shield
I think this notebook could be used if anybody wants to try it. I am also open for any correction
void.ipynb (262.8 KB)
Wahid