Dear Agnieszka
Although I may not feel capable of answering about FLUKA technical details,
I might try to be useful addressing some issues I experienced when trying
to perform with FLUKA and other codes similar simulations as you described.
Ideally, current ratio obtained from experimental ionization chamber
measurements at different photon beam energies may be reasonably approached
by deposited energy ratio calculated by MC, but recombination and leakage
current effects could drive to differences. These discrepancies are energy
dependent, because mentioned effects (among others like specific
geometrical properties and, of course, gas thermodynamics conditions as
indicated by Alfredo) have relative higher impact at low energies.
Calculating ionizations within air volume (radiosensitive volume) would be
prefereable.
FLUKA experts may guide you if FLUKA includes tally for ionizations (like
USRBIN or other type), but being a powerful code I guess FLUKA provides
some mechanisms for accounting for ionizations (perhaps modifying some
specific subroutine).
Best regards
2018-07-04 15:10 GMT-04:00 Agnieszka Witkowska <
witkowskaagnieszka07_at_gmail.com>:
> Dear Francesco and Alfredo,
>
> Thank You for reply. Indeed I should change the density, I simply forgot
> about it.
>
> In real life experiment charge generated in ionization chamber was simply
> scored on a anode and chamber's response for different beam energies was
> compared (ratio of scores for different energies). I am trying to get those
> ratios however in Fluka I cannot directly obtain current measured by
> ionization chamber. I came up for the idea to score energy deposited in gas
> and divide such scores obtained for different energies (I was hoping it
> will show the same results as for ratio of the current).
>
> Can You please advise how to model in Fluka this life experiment? I do not
> need to get the results of the current, just the ratios. I was also
> considering to use DETECT card, however I am not sure how it works.
>
> Best regards,
> Agnieszka
>
> 2018-07-03 8:53 GMT+02:00 Alfredo Ferrari <alfredo.ferrari_at_cern.ch>:
>
>> Dear Agnieszka
>>
>> I am not sure it really matters for your problem, however if I understand
>> your input correctly, you want to have Argon at 25 atm as sensitive gas,
>> you (correctly) set the gas pressure to 25 atm with MAT-PROP, but you left
>> the density in the corresponding material card to the one at 1 atm, which
>> is changing quite a bit the energy deposition.
>>
>> Please forgive me if I misinterpreted something, I only gave a summary
>> look at your input.
>>
>> Alfredo
>> +----------------------------------------------------------------------+
>> | Alfredo Ferrari || Tel.: +41.22.76.76119 |
>> | CERN-EN/STI || Fax.: +41.22.76.69474 |
>> | 1211 Geneva 23 || e-mail: Alfredo.Ferrari_at_cern.ch |
>> | Switzerland || |
>> +----------------------------------------------------------------------+
>>
>> On Sun, 1 Jul 2018, Agnieszka Witkowska wrote:
>>
>> Dear Fluka Experts,
>>> I am trying to lead in Fluka real life experiment with usage of
>>> ionization
>>> chamber. I am measuring energy deposited in gas of the device. in real
>>> life
>>> experiment source of radiation was placed 2 meters from centre of
>>> ioniztion
>>> chamber.
>>>
>>> I assume that I do not know how to define correctly beam source to make
>>> it
>>> similar to real conditions. I defined monoenergic, rectangular beam with
>>> x
>>> and y beam 200cm to make sure that the whole device will be surrounded by
>>> radiation.
>>>
>>> I have obtained really strange results. With increasing energy the energy
>>> deposited in each simulation is increasing as well, what does not match
>>> with
>>> life experiments, as in some point no more electrons should be generated
>>> in
>>> gas.
>>>
>>> Can You please check my input file and advise what I am doing wrong? Or
>>> maybe I am missing some physics?
>>>
>>> Below I attached obtained results:
>>>
>>> beam energy [GeV]
>>> deposited energy
>>> 0,000059
>>> 1,79E-08
>>> 0,000186
>>> 2,68E-08
>>> 0,000667
>>> 5,73E-08
>>> 0,00117
>>> 8,85E-08
>>> 0,005
>>> 3,07E-07
>>> 0,01
>>> 5,11E-07
>>> 0,02
>>> 7,19E-07
>>> Best regards,
>>> Agnieszka
>>>
>>>
>
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Medical Physics
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Received on Thu Jul 05 2018 - 12:04:32 CEST