RE: Spontaneous decay of cobalt-60 and random BEAMPOS?

From: Giuseppe Battistoni <>
Date: Mon, 26 Apr 2010 10:13:27 +0200

Dear Georgios
our CERN colleague T. Otto correctly alerts that there is a mistake in
my answer about
the sampling of position in the spherical shell:

Since the subroutine RACO samples a point on the surface of a unit sphere,
in order to score correctly the radius. you must sample R from a
probability distribution proportional to R**2 and not to R, otherwise
there is a higher concentration
towards the internal layer of the shell
The reason is the that the volume element in spherical coordinates is
R**2 dR dcosTheta dPhi

-----Original Message-----

[] On Behalf Of Giuseppe Battistoni
Sent: Saturday, April 24, 2010 12:13 PM
To: Georgios Tsiledakis
Subject: Re: Spontaneous decay of cobalt-60 and random BEAMPOS?

Dear Georgios
This is a typical problem that can be tackled only by means of user
In particular you have to use the SOURCE command and program
the source.f routine, which will be compiled and linked to build a
FLUKA executable for your program.
In the source routine you will inject the two monochromatic photons
originanting in a random position in the Co shell and emitted according
to an isotropric angular distribution.
It's easy but not totally trivial if you never did it before.
You have to study the chapter about user routines in the manual, learn
how to call
the random number generation functions of FLUKA and implement the
correct algorithms to sample correctly position and emission angles.
Beyond the manual I recommend the slides of one of the lectures at
previous FLUKA courses.
For instance:

In your case, the non usual situation is that you must inject two
particles (photons) for each event.
In order to achieve that, inside source.f you have to:
a) define the energies of the 2 photons, for instance using a vector
with 2 components
      Egamma(1) = 0.00117
      Egamma(2) = 0.00133
      IJBEAM = 7 ! that means photon

b) insert a loop before the fundamental instruction NPFLKA = NPFLKA +
something like:
    DO N = 1, 2
       NPFLKA = NPFLKA + 1
   END DO ! (the END DO instruction gose just before the final RETURN
of source.f)

c) Inside the loop, at the first cycle you give as energy Egamma(1), at
the second Egamma(2)
Something like:
* Kinetic energy of the particle (GeV)
         TKEFLK (NPFLKA) = Egamma(N)
* Particle momentum
    & + TWOTWO * AM (IONID) ) )


All this is trivial if you have experience of coding and have a careful
studying of these advanced
topics in FLUKA. Furthermore let me stress the importance of defining
the correct algorithms
for sampling position and directions.
For both cases there is a FLUKA routine which might be useful. If you
    CALL RACO(tx,ty,tz)
you will find in tx ty and tz 3 random numbers which represent the
direction cosines
of a random direction in space. These are necessary not only to sample
direction, but also position,
because they represent also a random point on the surface of sphere or
unit radius.
By scaling with an actual radius values (sampled uniformly between your
Rmin and Rmax) you get
what you need.
Let me also recall the importance of working always in double precision.

If you will need help for further understanding please write to the list

or look at for some
expert colleague who might explain directly the matter
Good luck!
    Giuseppe Battistoni

Georgios Tsiledakis wrote:
> Dear FLUKA experts,
> I have one spherical gas volume ,69cm radius, Ar-CH4 2%.
> The outside spherical shell of 1cm width (Rin=69cm, Rout=70cm) is made
> of a compound material Copper + 1 % Cobalt-60.
> Cobalt has 2 gamma rays with energies of 1.17 and 1.33 MeV, and these

> through
> Compton in Copper creates in our (gas)detector a background.
> One trick to estimate that background is to place by hand an
> isotropic
> photon of 1.33 MeV in the middle of the spherical copper shell via
> cards. That what I did and with the EVENTBIN card I am able to plot
> energy deposition
> per primary.
> My questions are the following:
> 1)
> Is any way to implement easy this spontaneous decay of Cobalt and use
> as a gamma BEAM?
> I do know know how to use these gammas from the cobalt as a BEAM imput
> card... Should I use in the beginning Co-59 and activate it with a
> source? If yes, what energy? I tried to use RADDECAY but in vein...
> How I could be sure the atoms of cobalt that are ramdomly distributed
> being 1%
> in the copper shell decayed and transport gammas/betas in the gas?
> I am interested to use the same EVENTBIN file...
> I provide the input I have used with photon energy of 23 keV just for
> test.
> 2)
> How I could force the isotropic photon of the input I use have not one

> specific position given by BEAMPOS card BUT it can come from every
> possible position of the spherical shell made of copper (Rin=69cm,
> Rout=70cm)? I do not know fortran and I wonder if one of you has any
> source.f who can do that.
> Thank you very much in advance
> Every piece of help is highly appreciated
> Best regards
> Georgios Tsiledakis
Received on Mon Apr 26 2010 - 11:11:09 CEST

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