I have attached the input file.
I am testing a deuteron beam hitting a titanium-trititium target for neutron production. Energy at 150 keV, and I have the deuteron cut set to 10 keV and multiple scattering turned off so it should track the deuteron down to 10 keV.
The TiTr (titanium tritium) target density does not appear to make any difference to the results. I get the exact same inelastic secondaries (fusion events) from DT regardless of the material density for TiTr.
Have I incorrectly defined this, or is something else happening in the model physics I’m not aware of?
As a side note, I miss the point of doing so, which by the way is not what your MULSOPT card actually does (as you implemented it, it rather alters the Molière screening angle).
In fact, over the tiny deuteron range in your target, a larger target density, while increasing their reaction probability (i.e., reducing their inelastic scattering length in TiTr, which is printed in the material table of the output file), reduces their path correspondingly, leading to the same number of reactions.
As for your USRBIN scoring, I guess you meant to get 4-HELIUM and not 3-HELIUM.
Finally, with the default neutron point-wise treatment, all LOW-MAT cards are useless.
I attempted to use the MULSOPT card to turn on single scattering, as per 2.3. Transport — FLUKA Manual so that I could track the deuterons down to 10 keV, as it says in the manual.
That makes sense about step length and density, appreciate the explanation.
In general, do you think Fluka should give good fusion results at these relatively low energies? 150 keV fusion events are a fair bit lower than the default GeVs.
That’s indeed an appropriate intention, but to do so you need to select the SDUM GLOBAL (and not MLSH-OFF), with WHAT(4)=WHAT(5)=1.0 and WHAT(6)=1001.0 (see the card manual at my above link).
We approach here the lower limit of FLUKA’s applicability, but the d(t,a)n reaction cross section at these very low energies was recently made accurate with respect to available data, so I’d expect a reasonable outcome.