Re: energy deposition in beryllium target

From: Anna Ferrari <anna.ferrari_at_lnf.infn.it>
Date: Tue, 16 Feb 2010 10:07:04 +0100 (CET)

Hallo Tristan,

in your input file I did not find an error, that could explane the big
difference you found by comparing your results with the ones, from another
simulation code.
>From your USRBIN results you should have obtained a plot like the one I
put in attachment, in the R-Z plane. To do this plot I used not your 20
bins in phi but the (default) 1 bin, because of the azimuthal simmetry of
the
problem: remember that in each bin the density of the deposited energy (in
GeV/cm3 per primary particle) is calculated by averaging on the volume of
the bin; this means that you inefficiently repeat the average in 20
volumes - each with the same probability of proton interactions - instead
of doing the average in one bin.

A question is: how did you calculate the total energy deposited in your
target? You can certainly do the sum of the energies deposited in all your
cells (having multiplied the energy densities by the volume of each cell),
but a very fast way to do this is to use another USRBIN card with only
1 bin in R, z and phi, corresponding to the dimensions of your dump. In
this way you directly get the average energy density calculated over all
the dump, and you can obtain the total deposited energy simply multiplying
by the dump volume.

I would like to add some minor considerations about your input file, that
only marginally affect your calculations:
- I have the impression that in your simulation the 60 GeV
  proton energy is "thought" as the total energy and not
  the kinetic energy of the beam...
  if I'm right, remember that, even if in this case the
  difference is neglectable due to the high energy of protons,
  the what(1) negative sign in the BEAM card refers
  to the kinetic energy of the beam, and not to the total energy.
- you put the origin of your beam at the boundary between
  two regions: your vacuum cylinder and your target. This is not
  good, try to put the origin a bit before the boundary.

Hope it helps,

Anna

------------------------------------------
Anna Ferrari
Inst. for Safety Research/
Inst. for Radiation Physics
Forschungszentrum Dresden-Rossendorf e. V.
PF 510119 D-01314 Dresden (Germany)

>
> Dear Fluka Users,
>
> I am trying to calculate the energy deposition in a cylindrical pure
> beryllium target as a result of a monoenergetic 60GeV proton beam. The
> beam has a Gaussian distribution with sigmax=sigmay=3.5mm and enters the
> target normal to the circular cross section of diameter 2.1cm. The
> target is a 100cm long cylinder. I have got some results for total
> energy deposition but they are about 40% less than MARS results obtained
> by colleagues. I would appreciate it if you could take a quick look at
> my input file (attached) and see if I am neglecting anything important
> for calculation of total energy deposited in the target.
>
> Kind Regards
>
> Tristan
>
> Tristan Davenne =20
> STFC Technology
> G19 R65
> Rutherford Appleton Laboratory
> Chilton, Didcot, Oxfordshire OX11 0QX, UK
> Tel: +44 (0)1235 445485
> Email: tristan.davenne_at_stfc.ac.uk <mailto:t.r.davenne_at_rl.ac.uk>=20

Received on Tue Feb 16 2010 - 11:02:35 CET

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