Re: Question from Irina Semenova: Energy deposition in FLUKA (fwd)

From: Alberto Fasso' (Alberto.Fasso@cern.ch)
Date: Mon Dec 16 2002 - 15:26:12 CET


On Sat, 14 Dec 2002, Giuseppe Battistoni (for Irina Semenova) wrote:

> ......
> I have a few questions conserning FLUKA.
> ......
> 1.
> I want to have energy deposition in plastic scintillator from neutron beam, and
> I used EVENTBIN card for that (DEFAULTS ... CALORIMEtry):
>
> EVENTBIN 10. 208. 51. 50.8 12.7 688.86 FRONT01
> EVENTBIN -50.8 -12.7 678.7 1. 1. 1. &
>
> Results have been printed in ASCII output file.
> In this file, for example, for event #37 we can see :
>
> Binning n: 1, " FRONT01 ", Event #: 37, Primary(s) weight 1.0000E+00
> 3.2116E-02
>
> Because I want to know the energy depositions sorted by type of particle,
> I inserted few lines in GEODEN routine (under ENTRY GEODEN):
>
> ...........
>
> * User defined binnings
> IF ( LUSBIN .AND. LSCORE ) CALL USRSCO ( IJ, XA, YA, ZA, MREG,
> & RULL, ICALL, LLO,
> & ECONTR )
> *
> IF (MREG .EQ. 3) THEN
> XTUP(1)=INT(WEIPRI)
> XTUP(2)=JTRACK
> XTUP(3)=RULL
> CALL HFN(77,XTUP)
> ENDIF
>
> .............
>
> After processing ntuple, I got the following information for the same event #37:
>
> Event # 37
> --------------------------
> Fluka name Fluka number RULL
>
> 4-HELIUM -6 0.0199890565
> 3-HELIUM -5 0.
> TRITON -4 0.
> DEUTERON -3 0.
> PROTON 1 0.00140738138
> ELECTRON 3 0.
> POSITRON 4 0.
> PHOTON 7 0.
> NEUTRON 8 0.00228806818
> PION- 14 0.
> ENERGY 208 0.00843147002
> ------------------------------------------
> SUM 0.0321159773
>
>
> As you can see the SUM (of energy depositions) equals to
> the number printed in the output file (EVENTBIN card).
>
> My question is:
> What does the energy deposition from "generalized
> particle 208(ENERGY)" mean in this content? Is it some physical
> energy deposition or I have to subtract this value from the total
> energy deposition?
>

Energy deposition with particle code 208 means kerma energy, i.e. energy
transferred to particles which are not better identified and are assumed to
deposit all their energy at the point of production.
This happens mainly in low-energy neutron reactions where the recoils or
heavy fragments are not explicitely produced and transported.
In general, it is safe to assume that this kind of energy is deposited
very close to the point of production: however, note that "kerma" is intended
here in a wide sense of "residual excitation energy", including not only the
emission of charged particles, but also of gammas in the case of those nuclides
for which gamma production cross sections are not available.
Check on the manual, chapter 16, for instance:
 186W Tungsten 186 293 K ENDF/B6R8 Y 186-W 74 186 293 Y
    Re Natural Rhenium * 293 K ENDF/B-VI Y RHENIUM 75 -2 293 N
The "Y" or "N" in the last column indicates whether gamma production is
included in the cross section data.
The fact that in some cases gamma energy is deposited at the point of production
instead of being transported can lead to a more or less important approximation
in the dose distribution. It is recommended to check the list of cross sections
if this is judged to be a critical issue.

I would like also to point out that the concept of "energy depositions sorted by
type of particle" can perhaps be useful but is not well defined, since it
depends on the threshold which has ben set for delta ray production. In the
limit for this threshold tending to zero, ALL THE ENERGY IS DEPOSITED BY
ELECTRONS!

> 2.
> How does Birks parameter apply for particles with more
> than 1 charge unit in FLUKA?
>
> For example, in GEANT (subroutine gbirk.F):
> ........
> C --- correction for particles with more than 1 charge unit ---
> C --- based on alpha particle data ...
> ....
> IF (ABS(CHARGE) .GE. 2.) RKB=RKB*7.2/12.6
> ....,
> where RKB -first Birks parameter.
>

In FLUKA, the Birks model is implemented as Eq. (6.12) in "The Theory and
Practice of Scintillation Counting", by J.B. Birks, Pergamon Press, Oxford
1964. In this equation, derived from the analysis of Chou (Phys. Rev. 87, 904
(1952)), the quenching effect depends only on the stopping power S:
                dE' = dE/(1 + BS + CS**2)
(dE = energy loss, dE' = energy loss corrected). B and C are constants
provided by the user.
Therefore, for the same dE/dx, the correction is the same, independent of
the charge of the particle. Fig. 6.3 in the book of Birks, where many
experimental data are reported, seems to confirm that there is no need to
apply any correction for particles with more than 1 charge unit.
But perhaps you are aware of more modern evidence for this?

  Alberto FassÚ

>
> Thanks for your help.
>
> Sincerely,
> Irina Semenova.
>
> stepi@jlab.org
> Kent State University ,OH

-- 
Alberto FassÚ
CERN-EP/AIP, CH-1211 Geneve 23 (Switzerland)
Phone: (41 22) 767 2398    Fax: (41 22) 767 9480   Alberto.Fasso@cern.ch


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