Dear FLUKA experts,
Thank you to all who replied. I have resolved the issue.
Have a good weekend,
On Wed, Jun 27, 2018 at 5:27 AM, Mauro Valente <mauro.valente_at_gmail.com>
wrote:
> As Paola pointed out, mean excitation potential <I> of liquid water that
> was suggested as 75.0eV by protocols and worked reasonably well for photon
> and electron beams may not be suitable for protons or ions.
>
> Accordong to our recent research combining theoretical and simulations
> approaches along with comparisons with experimental data (in water
> ionizations for proton beams within clinical energy range), a suitable
> value for <I> is (77+-1)eV.
>
> FLUKA main code has the great advantage of allowing user to (carefully)
> change <I> value, so I may suggest to repeat your calculations modifying
> this parameter that strongly affect stopping power.
>
> best regards,
>
>
>
> Il giorno mer 27 giu 2018 alle 08:39 paola sala <paola.sala_at_cern.ch> ha
> scritto:
>
>> Hi Ryan,
>> on your slab dimensions, stopping power is constant up to the 4th digit.
>> The difference you see is due to nuclear interactions . You can see in
>> the .out file that there are some (few) of them. You can check by
>> yourself, using the THRESHOL card to turn off inelastic interactions.
>> If you are interested in precision, ICRU recently re-evaluated the
>> stopping powers for some materials, including water. This essentially
>> because the mean excitation energy (I) has been reevaluated to be 78 eV
>> instead of 75.
>>
>> https://www.nist.gov/sites/default/files/documents/2017/04/26/newstar.pdf
>>
>> To get these new values with FLUKA one should use the MAT-PROP card and
>> change the value for I.
>>
>> Hope this helps
>> Paola
>> On 06/27/2018 11:07 AM, Francesco Cerutti wrote:
>> >
>> > Hi Ryan,
>> >
>> > you are missing the fundamental concept that stopping power is not
>> > constant. It's increasing for decreasing energy (your proton is losing
>> > energy through the slab), which explains the higher energy deposition
>> > you found.
>> >
>> > Moreover, note that your expectation misses also the fact that delta
>> > electrons, generated by proton induced ionization and contributing to
>> > the proton stopping power, may actually leave your reference volume
>> > and deposit some energy outside.
>> >
>> > Kind regards
>> >
>> > Francesco
>> >
>> > **************************************************
>> > Francesco Cerutti
>> > CERN-EN/STI
>> > CH-1211 Geneva 23
>> > Switzerland
>> > tel. +41 22 7678962
>> > fax +41 22 7668854
>> >
>> > On Wed, 27 Jun 2018, Ryan Brosch wrote:
>> >
>> >> Dear FLUKA experts,
>> >> I have a simple setup of a 200 MeV proton beam incident on a 1mm slab
>> of
>> >> water. I am scoring energy deposition with SCORE.
>> >>
>> >> The stopping power for a 200 MeV proton is 4.491 MeV/cm or 449 KeV in
>> >> a 1mm
>> >> slab.
>> >>
>> >> However, SCORE shows about 463 KeV of energy deposition, 14 KeV more
>> >> than
>> >> expected. This is to much energy to be from nuclear stopping power.
>> >>
>> >> Am I missing some physics here? Surely the energy deposition should be
>> >> almost entirely due to inelastic coulomb scattering and should just be
>> >> dE=(dE/dz)dz where dE/dz is the stopping power.
>> >>
>> >> Thanks very much,
>> >>
>> >> --
>> >> Ryan Brosch
>> >> Ph.D Candidate
>> >> Department of Physics
>> >> Arizona State University
>> >>
>> >>
>>
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>> --
>
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> Prof. Mauro Valente, PhD.
>
> Medical Physics
>
> IFEG - CONICET &
> University of Cordoba
> Argentina
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--
Ryan Brosch
Ph.D Candidate
Department of Physics
Arizona State University
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Received on Sat Jun 30 2018 - 16:29:29 CEST