Re: [fluka-discuss]: Proton beams: deltarays artefacts

From: paola sala <>
Date: Fri, 11 May 2018 10:01:13 +0200

Dear Ana
as a general rule, it is never a good ida to set different delta ray or
transport thresholds in neighboring "interesting" regions, because the
electronic equilibrium will be lost. Think to your case: deltas are
produced only in one part of the target (let's call T10 , so they can
travel to the other parts, depositing energy far from the production
point.  T1 instead will not receive similar contibutions from the other
target segments, where deltas are not produced --> unbalance.

Why then in your case you get more energy ( would expect less in T1 from
previous consideration) ? Probably because there is a typo in your
input, the average ionization energy is never changed for medium WATER1,
while it is changed for medium WATER.

As I always say, ALWAYS look at the output file and check:
  Material n.    26(WATER   ) matched to WATER

  *****   dp/dx : material number  26 "WATER   "    *****

    ***** Average excitation energy : 7.8000E+01 eV, weighted Z/A :

Material n.    27(WATER1  ) matched to WATER

  *****   dp/dx : material number  27 "WATER1  "    *****

    ***** Average excitation energy : 7.5000E+01 eV, weighted Z/A :
5.5508E-01                *****

hope this helps (I did not do the final check)

On 05/01/2018 05:20 PM, Ferreira De Almeida Lourenco, Ana wrote:
> Dear Fluka experts,
> I'm simulating a SOBP in water with different deltaray thresholds as
> it can been seen in figure 1 below. The most energetic secondary
> electrons have a short range of <1 mm and therefore all energy
> transferred to electrons can be regarded as absorbed locally, thus,
> there is no difference between a depth dose-curve when using the
> default 100 keV deltaray threshold (green curve) or using an infinite
> threshold (blue curve). The curve in red results of a simulation with
> different transport parameters where in the middle of the SOBP (in the
> region between 14-16 cm) there is a "more accurate" transport. Figure
> 2 shows the middle of the SOBP in more detail. In this region,
> particles are transported with smaller step sizes and electrons are
> transported down to 1 keV. These parameters were optimised in previous
> simulations to obtain a particle transport accuracy better than 0.15%,
> important to model the response of ionization chambers.
> Looking at the results in figure 2, it seems that there is an artefact
> in the energy balance. Why is the dose higher in the middle of the
> SOBP for the simulation with a more accurate energy transport? How can
> I correct for this artefact?
> Attached the input files and the source file.
> Many thanks,
> Ana
> Fig 1
> -----------------------------------------------------------------------------------------------
> Fig 2

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Received on Fri May 11 2018 - 11:59:54 CEST

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