# Region value of USRBIN and 1D projection

Dear FLUKA experts,
The attachment is my project file.I want to use USRBIN named “count” with “region” to get total photons that get into the region.After run the file,I change the .bnn file to ASCII and get the value 2.5086E-02,then I get 1D project of USRBIN named “photon”,if I understand it right ,the Y-axis is 1/cm^2*per primaries.The maximum value of the curve is about 70,my question is below:
for one binning,the fluence should be 70 and total fluence should be the area ,not equal to 2.5086E-02,why the reason?
mix.flair (3.5 KB)

Dear FLUKA experts,
Except use USRBIN with “region”,is there any simple way to count total number(fluence) of specific geometry region(at least get the value)?

Hi!

On the manual it is written the following regarding USRBIN with “Region” as scoring type:
“The results from USRBIN are normalised per unit volume and per unit primary weight, except region binnings and special user-defined binnings, which are normalised per unit primary weight only,”.
Since the fluence is calculated in terms of track length (cm), in case you ask for region type the units of the output values is given in “cm per unit primary weight”, while the R-phi-Z type is given in “cm-2 per unit primary weight”. Therefore, in the first case you have to divide by the volume of the region in order to get the same units as in the second case.

For your second post, up to my knowledge, USRBIN with “region” is actually the easiest way to get the average fluence in a region.

Kind regards,
Marta

Remember that fluence is a density-like quantity (specifically tracklength density) and as such is not additive in the space (being an average over the considered volume).

Dear@msabateg ,
Thank you for your help，I use fluence‘s graph integrate its volume，the value sames equal.

Dear@ceruttif ,
That is to say,if I want to get total number of optical photon,II need to integrate the volume of the fluence’s 1D projection,right?

Please note that the total number of optical photons over a region is an ill-defined quantity that makes little sense. The number of particles ( = current ) is well defined on a surface, not inside a volume, where one particle fully traversing it cannot be counted as one particle generated there and absorbed right after.
Indeed, when you score a particle type with USRBIN by region, you get the total tracklength (cm) traveled by that kind of particles inside a geometry region. If you divide it manually by the region volume, you get the average fluence (cm^-2) over the region, which is not the number of particles.
When you score with a different USRBIN type featuring a Cartesian or cylindrical mesh, you get the average fluence in each 3D bin. Now, if you plot the results of that USRBIN as 1D projection as a function of one spatial dimension, say z, you get a fluence profile averaged over the other two spatial dimensions, i.e. the xy or r-phi 2D slice corresponding to a given z bin. This gives you the number of particles going through each 2D slice if you multiply it by the slice area (not volume).

Dear@ceruttif ,