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

From: Mina Nozar <nozarm_at_triumf.ca>
Date: Tue, 30 Aug 2011 20:19:57 -0700

Dear Francesco,

This is clear to me now. I have just finished a set of runs to
investigate the number of fissions as a function of the
converter thickness. It is interesting to see how the number of fission
doesn't change by much as a function of the
converter thickness since for thinner converter, the photo-fissions in
the target are happening from the photons
converted in the target.

I will now move on to suggestions below since in the final design, a
slab of Al or Cu will be used to stop the remaining
electrons after the converter.

Wish you the best and thank you again for the explanations,

Mina

On 11-08-25 01:46 AM, Francesco Cerutti wrote:
>
> 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 Sep 01 2011 - 10:34:16 CEST

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