Re: [fluka-discuss]: USRBIN volume

From: Santana, Mario <msantana_at_slac.stanford.edu>
Date: Tue, 15 Jun 2021 16:29:02 +0000

For the calculation of fluences, or dose, etc. in meshes FLUKA 'knows' what the volume of a given voxel is (in rectangular or cylindrical coordinates it can be easily computed, as you indicated) and does use that volume. If scoring over regions, then the story would be different.

Please, note also that "The energy lost is apportioned among different bins according to the relevant step fraction." -( FLUKA MANUAL )

I am not sure about your other assumptions, but I'd say that this estimator has been extensively benchmarked.

-M

________________________________
From: owner-fluka-discuss_at_mi.infn.it <owner-fluka-discuss_at_mi.infn.it> on behalf of Ryan Brosch <rbrosch_at_asu.edu>
Sent: Tuesday, June 15, 2021 6:34 AM
To: fluka-discuss_at_fluka.org <fluka-discuss_at_fluka.org>
Subject: [fluka-discuss]: USRBIN volume

Dear FLUKA experts,

I am trying to understand how FLUKA determines the volume when calculating dose in USRBIN (228). Does FLUKA calculate the energy deposited in a volume element, then divide by the volume of that element to get the dose?

I ask because for a dose binning into volume elements in cylindrical coordinates with symmetry in θ a volume element ends up as V=dzπ(r2)^2-dzπ(r1)^2.

For a proton (or other charged particle) beam incident normal to the end of such a cylinder (in the z direction) one expects a gaussian fluence distribution in n r due to coulomb scattering. The energy should therefore be normally distributed along the fluence distribution as it passes through each cylinder element with thickness dz.

The volume of each cylinder element increases with r, however, and dividing the energy deposited in each element by the volume of that element produces a dose distribution which is non-gaussian in r.

However, when scoring dose distribution using USRBIN in FLUKA, I consistently obtain gaussian distributions in r.

So my question is, am I considering FLUKA's dose calculation wrongly in that energy deposited in each volume element are not divided by the volume of each element? If not, then what volume is considered for the dose calculation? Is it the volume of the entire region to be scored?

Thanks very much for your kindly assistance.

Ryan Brosch
Arizona State University


__________________________________________________________________________
You can manage unsubscription from this mailing list at https://www.fluka.org/fluka.php?id=acc_info
Received on Tue Jun 15 2021 - 20:02:17 CEST