# Application of LAM BIAS card

Dear experts,

I have made a simulation with 16 MeV proton beam incident on a 1.24 mm of Al target.
I noted few observations:

1. From .out file, it was printed that inelastic scattering length of proton of 16 MeV energy in Al is 21.27 cm (please find the attached image).
2. From SRIM software, projected range of 16 MeV proton in Al target is 1.42 mm.

In view of this, I have few queries:

1. When we call a target as thick target or thin target, this is with respect to range, not with respect to inelastic scattering length, right ? Does Fluka also print range of particle (defined in the beam card ) in various material ?

2. In my present case, I feel I have to use LAM BIAS card to improve interaction statistics. Now, in ˣ λ inelastic, I can use 0.02 to reduce the scattering length by a factor of 50. In this case, if I use +0.02, then no Russian roulette is activated, but if I use -0.02, then, primary proton will survive/die playing Russian roulette. In this regard, my query is how to decide what I have to choose from plus or minus sign ? Should I try with plus sign first and if it takes large simulation time, then should I go for minus sign value??

Regards,
Riya

Dear @riya,

1.The definition of thick or thin target depends on the particular situation.
For your case, It is clearly more logic to associate the “thickness” of the target to the projected range. The projected range is defined as:

“Average value of the depth to which a charged particle will penetrate in the course of slowing down to rest”

Considering this, the majority of your protons will end up in the Aluminum due to the coulomb interaction with the electrons. Then, for this case a target of ~2mm would be “thick”, as you can observe in the following simulation:

But what if we have a 1 GeV proton instead?
Now the projection range would be ~6m and the inelastic scattering length ~40cm.
Here would be more reasonable to associate the thickness to the inelastic scattering length.
And No, FLUKA does not provide projection range.

1. You have a good feeling, the LAM BIAS will improve your interaction statistics. I do not think you should be worried about the simulation time. Killing or not the primary particle, for your case, should have a negligible impact. I just ran your case and both options gave me a time/primary of 0.2ms .

I hope this helps.
Cheers,
André

2 Likes

Thank you @adonadon for the reply. Adding LAM Bias, I am attaching my input here which gave me some error. It was working I guess, before I updated my ubuntu system to 22.04 version recently and moved to the new flair version as well. Also surprisingly, I cannot select ‘mass’ in the compound card. No matter how many times, I am clicking on the mass, it is remaining in the ATOM state.

I am not sure if I should post this query here itself. If required, please move it to a different thread.

Note: I have used .deb version of fluka and flair during installation.

input_1.flair (3.2 KB)
input_1.inp (4.6 KB)

Regards,
Riya

Dear @riya,

First of all, it does not change because you have to add a ‘-’ in WHATS 1 and 3.

And second. The error you get is because you are not providing the information of the beam intensity (WHAT2 for your case) in the IRRPROFIle card.

This presentation of the last fluka course may help you (in particular page 20):

Cheers,
André

2 Likes