Re: [fluka-discuss]: Interactions at surface between air and air

From: Kilian Baumann <baumann.kilian_at_gmail.com>
Date: Mon, 5 May 2014 14:34:13 +0200

Dear Vittorio and Luigi,

thank you for your answers!
Since the energy is given in GeV/n (n: nuclear unit mass) with a nuclear
mass of 12 (6 protons and netrons each for carbon-ions), I should state
0.960 GeV in WHAT(1) to get 80 MeV carbon-ions?
And in the graphs the Y-axis is stating the dose I have measured with the
USRBIN (unit 22 BIN) called "zoom".
However, when using a sufficient amount of primaries, can I ignore the
effects at the surface?
And concerning the different ransom seed: when simulating, I used 50 runs,
while each run gets a different random seed. To get the primaries, I only
changed the corresponding number in the start card. Is that what you meant?
Thank you very much for your help!
Best regards,
Kilian


2014-05-05 14:00 GMT+02:00 Luigi Salvatore Esposito <
luigi.salvatore.esposito_at_cern.ch>:

> Hi Killian,
> maybe it is superfluous, but let me comment that the 80 MeV kinetic energy
> that you have set is *per nuclear unit mass*,
> as it is stated in the FLUKA manual (BEAM card, WHAT(1)).
>
> Luigi
>
>
> On 5 May 2014, at 13:23, Vittorio Boccone <dr.vittorio.boccone_at_ieee.org>
> wrote:
>
> Hi Kilian
>
> So I wonder, what exactly is happening around the surface between the
>> sourounding air and the air in the region. Are there any effects, because
>> FLUAK is perhaps switching between multi- and single-scattering? Or is
>> Fluka adapting path.lengths of the particles, when being near to a
>> regionborder?
>
>
> Yes FLUKA is doing it, but you can fully control this with the MCS
> parameters (see the manual for more details).
>
> I have a doubt on what exactly are you plotting on the Y-axis of the 1D
> graph? Is it a slice of the USRBIN, the central bin or what?
>
> But I think this is not your problem.
>
> Your curves for 5E5 events have large errors; the curves for 1E7 are
> compatible with the both the 5E5 ones and, if you look carefully, the
> curves for 1E7 primaries are in the middle of both curves realized with 5E5
> primaries.
>
> The position of the peak tells you that the energy is the same e
>
> You can try to run again one of the case with a different random seed
> and try to see which are the effects. Be sure to average a few bins around
> the beam.
>
> Best,
> V.
>
>
>
>
>
>
>
>
>
>
> On Mon, May 5, 2014 at 12:35 PM, Kilian Baumann <baumann.kilian_at_gmail.com>wrote:
>
>> Dear Vottorio,
>>
>> thank you very much for your answer!
>> I have attached the input-file. As you can see, I measure the dose along
>> the beam-axis in a waterphantom. In front of this phantom there is a region
>> (1 cm thick, called "ripple") containing air. The sourounding of my set-up
>> is also air. So technically, this region should have no influence at all.
>> In a second set-up I have just removed this region. The rest remains the
>> same.
>> When using <1E05 primaries (80 MeV cabon-ions) the depth-doses for these
>> two set-ups do not match within their errors around the bragg-peak. The
>> more primaries I use, the smaller the diefference gets until, when using
>> >1E07 primaries there is almost no difference left. (I have attached the
>> graphs. For a better overview there are only a few error-bars).
>> So I wonder, what exactly is happening around the surface between the
>> sourounding air and the air in the region. Are there any effects, because
>> FLUAK is perhaps switching between multi- and single-scattering? Or is
>> Fluka adapting path.lengths of the particles, when being near to a
>> regionborder?
>>
>> Thanking you very much in advance!
>>
>> Best regards,
>> Kilian
>>
>>
>> 2014-04-30 23:13 GMT+02:00 Vittorio Boccone <dr.vittorio.boccone_at_ieee.org
>> >:
>>
>> Dear Kilian,
>>>
>>>
>>>
>>>> When assigning the material of the
>>>> region to air, it should be as if there is no region at all (because
>>>> the enviroment and the region consist of the same material).
>>>>
>>> You assign it to air. Was it vacuum before or just the geometrical
>>> representation of the phantom was different?
>>> Which sizes are we talking about (meters, cm, mm or um?)
>>>
>>> However, the depthdose-curve (for <1E05 primaries) in the water-phantom
>>>> is significantly different to the depthdose-curve, when there is no
>>>> region.
>>>
>>> What do you meas about significantly different? Did you check the
>>> statistical error of the simulation?
>>>
>>>
>>>> However this effect gets lost, when using >1E07 primaries.
>>>>
>>> This is a sign that you are very much dominated by the statistical
>>> error with less then 10 Millions of particles. This is realistic because
>>> the dose in air requires typically a lot of statistics or larger averaging
>>> bins/regions.
>>>
>>> Your input file would be probably useful to check which are your
>>> physics setting and the scoring you are performing.
>>>
>>> Best,
>>> V.
>>>
>>>
>>> On Wed, Apr 30, 2014 at 10:05 PM, Kilian Baumann <
>>> baumann.kilian_at_gmail.com> wrote:
>>>
>>>> Dear Fluka-experts!
>>>>
>>>> I have discovered a (perhaps) strange result, when analysing the
>>>> depthdose-curve and fluence, when irradiating a waterphantom with a
>>>> region in front of it. My whole setup consists of the beam source (80
>>>> MeV carbon-ions), a water phantom and a region between waterphantmom
>>>> and source. The enviroment is air. When assigning the material of the
>>>> region to air, it should be as if there is no region at all (because
>>>> the enviroment and the region consist of the same material). However,
>>>> the depthdose-curve (for <1E05 primaries) in the waterphantom is
>>>> significantly different to the depthdose-curve, when there is no
>>>> region. However this effect gets lost, when using >1E07 primaries.
>>>> Furthermore I analysed the fluence at the surface of the region, so to
>>>> say at the surface between air and air and indepent on the amount of
>>>> primaries one can see a change in fluence at the surface.
>>>> My question now is, what FLUKA is exacly calculating near this
>>>> surface/region (perhaps some artefacts with single-/multi-scattering)
>>>> and if any effects are negiglibly if using a sufficient amount of
>>>> primaries.
>>>> Thanking you in advance!
>>>> Best regards,
>>>> Kilian
>>>>
>>>>
>>>
>>
>
> Luigi
>
> ------------------------------------
> Luigi Salvatore ESPOSITO
> CERN, EN-STI-EET
> tel: +41 22 76 79132
> fax: +41 22 76 68495
> skype: luillo76
>
>
Received on Mon May 05 2014 - 15:36:36 CEST