Disabling inelastic interactions in a region

Dear FLUKA experts,

I’m simulating scattering of gold beam on a thin gold target and I’m trying to score the background that is created by the elastically scattered beam particles. Is there a way to disable inelastic interactions only inside the target while leaving them on in the rest of the geometry? I’ve tried using the LAM-BIAS card and putting the biasing factor larger than one but that didn’t work.

Regards,
Ondrej

Dear @hofmanond,

Thank you for your question. Have you considered using the THRESHOLD card, which allows disabling the inelastic interactions below certain energy threshold in every region?

Moreover, could you provide a bit of extra information about the ion energy of your simulation? How about the gold layer thickness?

Regards

Mario

Dear Mario,

thanks for your reply.

Yes, I’ve looked into the THRESHOLD card, but it was no use to me as I need to disable the inelastic interactions only inside the target so that the elastically scattered particles behave normally (interact both elastically and inelastically) everywhere else.

To answer your other questions, the beam energy ranges from 2 to 11 A GeV and the target is 0.25 mm thick.

Regards,
Ondrej

Thank you @hofmanond,

Unfortunately, the functionality to disable the inelastic interactions per region is not available.There may be brute-force alternatives which might yield to effect you are looking for, but these are definitely not free of caveats.

One option can be suppressing all of the secondaries generated in the unwanted inelastic interactions happening in the region of interest. This can be done by means of mgdraw.f (USDRAW), filtering by the variables MREG and ICODE and setting the weight of the particles to zero. This way, only the stories of primaries free of inelastic interactions will be propagated after the target. The final quantitative results will probably need correction to adapt the initial number of primaries to the actual final primaries. In your example, the target thickness is approximately 1/100 of the inelastic length for gold and the given ion properties, so you may expect losing 1% of the primaries with this method.

Please let me know if this is helpful.

Regards,
Mario