Re: FLUKA: Question

[Alberto Fasso' <Alberto.Fasso@cern.ch>]

On Wed, 2 May 2001, foucher wrote:

> Dear FLUKA users,
> 
> I am trying to calculate the thermal neutron flux in different cells.
> For this purpose, I am using
> the USRTRACK card.
> My problem is that when I compare my results to others coming from
> different codes, the discrepancy is very important: 30 %.
> The materials where I wanted to have the thermal neutron flux is "Heavy
> Water", and water. The mistake is
> probably due to a bad definition of these elements in my input file.
> Is there anyone who has ever defined these materials ?
> If yes, could you give me the good input cards for the definition of
> thess materials and the peg files for these materials ?
> Thanks in advance.
> 
> Yann FOUCHER
> Paul Scherrer Institut

In the following example we define 3 types of water:
natural water, "light" water containing only 1H and no deuterium,
and heavy water containing only deuterium and no 1H.


*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....8
MATERIAL          1.   1.00797  8.988E-5        3.        0.        0.HYDROGEN
MATERIAL          8.   15.9994  1.429E-3        8.        0.        0.OXYGEN
MATERIAL          1.  1.007825  8.988E-5       19.        0.        1.HYDROG-1
MATERIAL          1.     2.014    1.8E-4       21.        0.        2.DEUTERIU
* Natural water
MATERIAL          0.        0.       1.0       18.        0.        0.WATER
COMPOUND          2.        3.        1.        8.        0.        0.WATER
* "Light" water (with only Hydrogen-1)
MATERIAL          0.        0.       1.0       20.        0.        0.LWATER
COMPOUND          2.       19.        1.        8.        0.        0.LWATER
* Heavy water (with only Hydrogen-2)
MATERIAL          0.        0.   1.10534       22.        0.        0.HWATER
COMPOUND          2.       21.        1.        8.        0.        0.HWATER


I remind you, however, about the following restriction (taken from the
manual):

           Important: the FLUKA hadron event generator cannot treat
           collisions with deuterium. Therefore it is necessary, for
           all materials containing hydrogen when used in hadronic
           problems, to define hydrogen as a monoisotopic material of
           A = 1 (set WHAT(6) = 1. in the MATERIAL card defining
           hydrogen). This is not necessary in pure electromagnetic or
           low-energy neutron problems. In problems with both high-energy
           hadrons and low-energy neutrons, it is possible (and
           recommended) to use monoisotopic 1-H above 20 MeV and
           natural hydrogen below. Note that the standard pre-defined
           FLUKA material is natural hydrogen and is not suitable for
           hadron transport above 20 MeV.


Here below you find PEMF inputs corresponding to the 3 types of water
described above.

COMP
 &INP NE=2, PZ=2.0, 1.0, RHO=1.00,IRAYL=1, ISSB=1, IEV=75.0, CBAR=3.5017,
   X0=0.24, X1=2.8004, AFACT=0.09116, SK=3.4773, &END
WATER
H  O
ENER
 &INP AE=0.611, UE=21, AP=0.01, UP=20. &END
PWLF
 &INP NALE=300, NALG=400, NALR=100 &END
DECK
 &INP &END


COMP
 &INP NE=2, PZ=2.0, 1.0, RHO=1.00,IRAYL=1, ISSB=1, IEV=75.0, CBAR=3.5017,
   X0=0.24, X1=2.8004, AFACT=0.09116, SK=3.4773, &END
LWATER
H  O
ENER
 &INP AE=0.611, UE=21, AP=0.01, UP=20. &END
PWLF
 &INP NALE=300, NALG=400, NALR=100 &END
DECK
 &INP &END


COMP
 &INP NE=2, PZ=2.0, 1.0, RHO=1.10534,IRAYL=1, &END
HWATER
H  O
ENER
 &INP AE=0.611, UE=21, AP=0.01, UP=20. &END
PWLF
 &INP NALE=300, NALG=400, NALR=100 &END
DECK
 &INP &END


Best regards,

    Alberto Fassò


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