I used USRBDX card to score the fluence of the proton, neutron and photon in particular position when 70,80,90,100 MeV proton beam hitting on Al and solid water target in turn.
The results of neutrons and photons are fine. But when I looked into the output of proton, there is no output when the energies of the proton beam are 70 and 80, while for the 90 and 100 MeV beams, there is output. As shown below
But for 100 MeV proton beam, there is response.
So I’m wondering why this happens because the difference between them is only the beam energy.
Another question is about the error of the Tot. resp. in the last picture, it is 49%. Does it means I need to increase the primary number?
Here are the input files for 70 and 100 MeV proton beam. zhuozhou_70.inp (2.5 KB)
The energy has nothing or very little to do with this difference, unfortunately.
Considering your problem and what you want score (essentially low-energy protons that are scattered at 90° by a very thin aluminium target and then collimated) the issue is related to statistics and transport settings that may be required for very thin materials.
Having a look at the lecture on electromagnetic interactions and
transport of charged particles would be a good starting point
Thanks for your kindly suggestion, and I studied the lecture on “electromagnetic interaction and transport of charged particles”. If I understand it well, I need to enable the DELTARAY card to change the threshold (default threshold is 100 keV)? Does this mean the target is thin, so the collision number is small, and then we need to change the threshold? if it is, how do I set the threshold? Is there any rule of thumb?
Dear experts,
Follow the last post Doubts about the output about the USRBDX card.
Thanks for Davide‘s kindly suggestion, and I studied the lecture on “electromagnetic interaction and transport of charged particles”. But there is still problem.
If I understand it well, I need to enable the DELTARAY card to change the threshold (default threshold is 100 keV)? Does this mean the target is thin, so the collision number is small, and then we need to change the threshold?
I set the threshold of the DELTARAY card to 1e-5 as the lecture suggested, the CPU time increased, but the result was still the same.
In order to see if the region I cared about had the proton fluence, I enabled the USRBIN card to score the proton fluence, and also, in case the proton fluence in region 1 is too small to score, I added region 2 ( refer to the size of the detector used in the experiment). The result of the USRBIN (figure1) indicates there is proton fluence in region1 and region 2, but if we see the result of the USRBDX, the proton fluence from the Be region to region 1 is still zero (figure2), and the proton fluence from void to region 2 is discrete distribution (figure3), which is different from the experiment result(figure4).
So I want to know why this happened?
If your input file correctly describes your experiment in terms of geometry and scoring, you can certainly try to adjust the delta-ray production threshold. Considering the very thin target you may want to switch on single scattering via MULSOPT as the Molière theory of multiple Coulomb scattering is not applicable in your case. You can find all the details in the FLUKA manual or in the lectures I have linked you above.
