Re: Is it possible to discard beam particles past a certain region?

From: Francesco Cerutti <Francesco.Cerutti_at_cern.ch>
Date: Thu, 25 Aug 2011 10:46:38 +0200

Dear Mina,

> Looks like setting the transport energy threshold for electrons to an energy
> above the beam energy will also not
> transport the secondary electrons and positrons below this energy.

correct, but the point was that electron transport thresholds can be set
on a region basis, through EMFCUT with SDUM blank. So Alberto recommended
to raise them in any region but the converter, transporting the electrons
only in the latter for photon production purposes, while I suggested to
create a dedicated fake region with high electron threshold downstream the
converter to kill the electron beam as well as the secondary electrons
escaping, this way keeping alive the electron/positrons generated by
photons in the U target (but do you need them?).

> I would have thought one could set the transport threshold for BEAMPART using
> the PART-THRES. I don't see BEAMPART as
> an option to use in for the PART-THRES.

No, BEAMPART is a generalized particle for scoring purposes only, and
moreover PART-THR, at least for the time being, is not intended for
electromagnetic particles.

> Francesco, is it possible to set the weight for BEAMPART in the usrmed
> routine? I haven't used user routines up to now
> but I will look into it.

Yes, BEAMPART's are identified by the generation number LTRACK=1 and you
can of course zero their weight WEE according to this condition. BUT for
your purposes, as already pointed out, this does not look at all needed
since an electron threshold selection on a region basis does more simply
the job. And then why would you like to kill just "primary" electrons and
not their Moller twins?

> Also, I have been looking at the BEAMPART distribution using the usrbin
> estimator. This does give me the beam particle
> distribution (electrons in my case) through the setup. And the ELECTRON
> distribution will show both the beam electrons
> as well as secondary electrons. Correct?

yes

Best

Francesco

**************************************************
Francesco Cerutti
CERN-EN/STI
CH-1211 Geneva 23
Switzerland
tel. ++41 22 7678962
fax ++41 22 7668854

On Wed, 24 Aug 2011, Mina Nozar wrote:

> Dear all,
>
> Thank you for your responses.
> Looks like setting the transport energy threshold for electrons to an energy
> above the beam energy will also not
> transport the secondary electrons and positrons below this energy.
>
> This must affect the secondary electron, as well as e+ and photon production
> as
>
> I would have thought one could set the transport threshold for BEAMPART using
> the PART-THRES. I don't see BEAMPART as
> an option to use in for the PART-THRES.
>
> Francesco, is it possible to set the weight for BEAMPART in the usrmed
> routine? I haven't used user routines up to now
> but I will look into it.
>
> Also, I have been looking at the BEAMPART distribution using the usrbin
> estimator. This does give me the beam particle
> distribution (electrons in my case) through the setup. And the ELECTRON
> distribution will show both the beam electrons
> as well as secondary electrons. Correct?
>
> As always, thank you very much,
> Mina
>
>
> On 11-08-24 07:57 AM, Francesco Cerutti wrote:
>>
>> Dear Mina,
>>
>>> My question is: is it possible to discard (stop) the primary beam
>>> particles (electrons) past the converter, in order
>>> to speed up the processing?
>>
>> yes, you can implement a very thin fake region filled with low density gas
>> downstream the converter and set there a high
>> electron transport threshold via EMFCUT (you need the gas since particles
>> cannot stop in vacuum). [This is a trick
>> already discussed by Alberto, though I cannot find now the proper link].
>>
>> As an alternative (needed for other particles to which EMFCUT do not
>> apply), you can selectively kill particles at a
>> boundary by zeroing their weight WEE inside the usrmed routine, to be
>> activated in connection with the downstream region
>> material via MAT-PROP (SDUM=USERDIRE, see the manual as well as the thread
>> http://www.fluka.org/web_archive/earchive/new-fluka-discuss/3152.html).
>>
>> I have then to warn you about the fact that the calculated photofission
>> yields are affected by the issue mentioned in
>> the release notes, responsible for significant underestimation especially
>> at low photon energies
>>
>> Best regards
>> Francesco
>> **************************************************
>
>> On 11-08-24 07:48 AM, Alberto Fasso' wrote:
>> Dear Mina,
>>
>> yes, it is possible to stop the electrons (but all electrons, you cannot
> discriminate between primaries and
>> secondaries)
>> when they enter a given region.
>> Set the electron transport cutoff very high in that region: higher than
> the
>> beam energy. Use for this purpose the EMFCUT command with SDUM blank, and
> set
>> WHAT(1) higher than the BEAM energy. If necessary, split one of the
> regions into two parts, if you want to stop the
>> electrons only in one of them.
>>
>> Using the same command, make instead WHAT(2) about 6 MeV in all 238U
> regions: you don't want to stop the photons, but
>> neither you want to track photons which are below the threshold for
> nuclear interactions (6.2 MeV for 238U).
>>
>> Regards,
>> Alberto
>> ***************************************************
>
>> On 11-08-24 01:45 AM, sujoy_at_vecc.gov.in wrote:
>> Dear Mina,
>>
>> In reply to ur previous mail, you can stop the electrons in the convertor
> by putting transport cutoff in the
>> convertor
>> more than the energy of the primary electron beam.
>
>>> Hi everyone,
>>>
>>> I am working on a setup, producing RIB out of photo-fissions in a Uranium
>>> Carbide.
>>>
>>> primary beam: electrons
>>> converter: to produce photons
>>> target: depleted Uranium Carbide
>>>
>>> In order to optimize the length of the converter, I look at number of
>>> fissions in the target as a function of the
>>> converter thickness (several runs with different converter thickness).
>>>
>>> My question is: is it possible to discard (stop) the primary beam
>>> particles (electrons) past the converter, in order
>>> to speed up the processing? I looked at the DISCARD card but this card
>>> doesn't allow for setting transport thresholds
>>> in a given regions or a set of regions.
>>>
>>> Thank you,
>>> Mina
>
>
Received on Thu Aug 25 2011 - 13:17:26 CEST

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