FLUKA: USRBDX results and running speed

[Fan Lei <flei@scs.dera.gov.uk>]

Dear Fluka team,

I am new to FLUKA and I am trying to use it to evaluate the neutron and
gamma ray fluxes
at Tungsten and Aluminium targets with proton incidents. I started with a
simple geometry:
1cm thick w spherical shell with a 2 cm Al shell outside. 1 GeV protons were
fired isotropically
from the centre of the sphere, and I am recording the neutron flux (current)
exiting the W shell as well
as the flux exiting the Al sphere. Please see the attached .inp file for
more details. Of course i have also created the correponding .pemf file. The
code excuted ok, but there are a few things I feel are not right
I am pretty sure they are due to some misuses of the code. I will appreciate
any help to identify the cause of the problem.  Here are a few of my
questions:

1) The execution took >110000 s cpu time on a PII-400 linux machine (with
256 MB memory), for
    1E5 events. This is many times slower than similar problem running on
the same machine
     with MCNPX.
2) What is the meaning of running cycles in FLUKA? the execution always go
through  5 cycles no
    matter how many events you are tring to to simulate, is this right?
3) To my surprise the output files are not changes from cycle to cycle, i.e.
wal005_fort.47 is exactly the
    same as wal001_fort.47. The same for the residual nuclei files.
4) looking at the neutron spectra in *_fort.47 and fort.48, it seems there
are cut-offs at both low and high
    energy ends (at ~ 3E-7 and ~ 0.5 -0.6  GeV respectively). Is this right?
if so how to change them?

Regards

Fan

-------------------------------------------------------------------
Dr. Fan Lei
Space Department, DERA
G081, A8 Building
Farnborough, GU14 0LX
U.K.

Tel  . 44-1252-393904
Fax.  44-1252-396330
email: flei@scs.dera.gov.uk



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wal.inp