RE: [fluka-discuss]: Best way to generate decay-like unidirectional electrons

From: Joachim Vollaire <>
Date: Tue, 17 Sep 2013 14:13:22 +0000

Hi Francesco

I check and in fact what I have suggested is not correct !
As you point out, with the source routine one modifies the direction of the isotope which is anyway at rest which has no effect on the decay product direction.
So the only alternative is with the source routine to sample from the energy from the decay particle spectrum. Or to use the "blcakchole approach" to filter particles within a desired solid angle. You could play with the region importance to split the particles which exit your setup and optimize the CPU time...

-----Original Message-----
From: Francesco Collamati []
Sent: 16 September 2013 11:04
To: Joachim Vollaire
Subject: Re: [fluka-discuss]: Best way to generate decay-like unidirectional electrons

Hi Joachim, and thanks for your reply.
I see that those lines in the source routine should help to select the direction of the particle selected from the BEAM card.
So, in my case it should be the direction of my father isotopes, that i would generate still, to obtain just the decay of the isotope instead.
In other words, am I correct to suppose that generating at rest isotopes will give no importance to those lines, being the decay process itself isotropic?
or am I misunderstanding something?
Thanks again


Il giorno 15/set/2013, alle ore 22:44, Joachim Vollaire <> ha scritto:

> Hi Francesco
> The most elegant and efficient (thus require some little time investment on your side) is definitely option 3 but the energy could be specified using the input file and isotope/HI-PROPE card (don't touch the energy assignment part of the routine).
> What you need to modify via the source routine is the direction cosine to ensure that the decay radiation goes into a beam like direction
> (this part of the input)
> * Cosines (tx,ty,tz)
> To ensure it is working properly, it is always good to make a sanity check using a scoring volume/surface (usrtrack/usrbdx) and an energy dependant spectrum without any interaction....
> Hoping it will work
> Cheers
> Joachim
> -----Original Message-----
> From: [] On Behalf Of Francesco Collamati
> Sent: 13 September 2013 12:48
> To:
> Subject: [fluka-discuss]: Best way to generate decay-like unidirectional electrons
> Dear Fluka experts, I write to you not exactly for a question, but I would say for an advice!
> I would like to simulate a pencil beam (thus unidirectional) of electrons having the energy spectrum of Ittrium-90 decay (endpoint ~2.3MeV).
> I thought a few ways to do it, but I would ask to you which one (of this, or of others!) is the smarter in term of CPU usage:
> - Use Isotope Card, that is properly producing electrons, but in the whole solid angle. Then I can kill all the particles not in the right direction via som,e biasing technique, or using a very small sphere of "blackhole" with a small hole.
> - I saw in Flair that in Beam card there is under DeltaP a choice named "function", that however seems not to be selectable. Is it deprecated?
> - Use a user routine to create particles in my direction, but I would need an algorithm to generate electrons from Ittrium decay..
> So, am I forgetting a smarter way to do this?
> Consider that I am going to use this simulation for simple small cases. So if option number 1 (the simplest for me to setup) is let's say just 50% slower than option number 3...!
> Thanks for your attention
> p.s. I am using the last fluka and flairs..
> Francesco Collamati
Received on Tue Sep 17 2013 - 17:05:50 CEST

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