Versions
FLUKA: 4-5.1
Flair: 3.4-5.2
Operating system: linux ubuntu
Description
Hello FLUKA Experts,I am simulating a nuclear physics setup aimed at obtaining the double differential cross-sections (d^2\sigma/dEd\Omega) of secondary particles (neutrons and protons) originating strictly from the first act of collision. I’m using proton beam with a kinetic energy of 160 MeV. My target is a sphere (Radius = 0.5 cm) made of Scandium-45 (^{45}\text{Sc}). Rather than implementing complex geometries, I am utilizing a single-cell approach combined with the LAM-BIAS card to artificially mimic an infinitely thin target. By setting the interaction length of secondary particles to an artificially high value (1.0\times 10^{3} ), I turn off secondary interactions completely. This ensures that I record a clean particle yield solely from the primary interaction vertex.For scoring I am using USRBDX. Is this a suitable approach for calculating cross sections? The yield Y(E,\theta) collected by USRBDX will be converted to the differential cross-section using the following relation:\frac{d^2\sigma}{dEd\Omega}=\frac{Y(E,\theta)\cdot\mathrm{Area} }{\mathrm{Number\ of\ target\ atoms}}\cdot\mathrm{Normalization\ factor} Since the target behaves as a quasi-thin layer due to biasing, the normalization factor is essentially 1/N, where N is the number of target atoms per \text{cm}^2
The Problem:
To ensure correct physics for the production of light fragments (deuterons, alphas, etc.) during the intranuclear cascade stage, I activated the coalescence model (COALESCE via PHYSICS).Upon running, the simulation immediately aborts with the error:Coalescence activated and beam above BME limit with no rQMDExecution terminated. Since the primary beam is a 160 MeV proton beam—which should be natively managed by PEANUT—I am unsure why the BME/rQMD threshold conflict is halting the run.
My Questions:
-
What is the root cause of this crash given a proton beam, and how should I properly handle COALESCE for this type of problem?
-
Are there better alternative practices or different scoring ideas within FLUKA to extract fundamental double differential cross-sections (\frac{d^2\sigma}{dEd\Omega}) or specific isotope production cross-sections directly, without relying on the LAM-BIAS thin-target approximation method? For example, is using USRYIELD, USERDUMP or tracking the primary interaction vertex preferred for this kind of nuclear data extraction?
Thank you for your insights and support!
Input files
work_test_01.inp (1.9 KB)