Re: problem of input

Dear Hamideh,
many issues in your input file have been already pointed out by
George, I would like to stress some other things.

1. About the production/transport em thresholds:

Since you did not specify the DEFAULTS card in your input,
sdum=NEW-DEFAults is assumed for this card. This means (see the manual)
that you *must* specify the transport threshold for electrons/positrons
and photons: in your input you have set only the production threshold
(sdum=PROD-CUT), and not the transport cut-off (you need again the card
EMFCUT with sdum=blank). This is a very important point: we (users) must
always be aware about the DEFAULTS and have always the control of the
production/transport settings.
Moreover, you have set the production threshold at 10 KeV... are you sure
that you want a such low value for a problem (I guess) of shielding? I
would say that a value of the order of magnitude of at least 1 MeV is
better both for production and transport... it is up to you, but be aware
of this.

2. About the photonuclear reactions:

In your case (I guess you want to calculate the fluence rate and then the
dose rate beyond the shielding) you must be sure to take into account all
the important contributions, that means not forget neutrons and muons (in
addition to the electromagnetic part of the radiation).
If you enable photonuclear reactions via the card PHOTONUC with
sdum=blank you will get the neutron contribution + the muons coming from
the pion decays (don't forget to use the LAM-BIAS card to reduce in the
appropriate way the hadronic inelastic interaction length). You can try
for example:

* ..+....1....+....2....+....3....+....4....+....5....+....6....+....7.
PHOTONUC 1.0 HYDROGEN @LASTMAT
LAM-BIAS 0.0 0.01 1.0 7.0

to enable the photonuclear reactions on all the materials defined in your
input, with a hadronic inelastic interaction length smaller by a factor
0.01.
It is important to say that there is another important contribution from
muons: at high energy the direct photonuclear muon production becomes
important. You take it into account by using another time the PHOTONUC
card with sdum=MUMUPAIR and by setting in what(2) the interaction length
biasing factor. I tried to run your input by switching on also this
channel and I saw this contribution (any clarification/correction from
Alberto Fasso', which wrote this part of the code, is welcome!!!)

3. About the scoring:

As already pointed out by George, when you have scored photon fluence via
USRBDX at the boundary crossing between concrete shielding and external
vacuum you got some result: if you look at the example_usrbdx_50_sum.lis
file you read something like 7.56 E-2 photons GeV-1 per primary (0.15
photon/primary by integrating on the energy bin). For sure you did not
want to use only one energy bin... so check your card with the help of the
manual. Be careful also with the similar card for the neutron fluence: I'm
sure you did not want to set the upper bound of your neutron energy
interval equal to 50 GeV, that has not meaning in your case.

I would like to suggest you to try to use also a USRBIN card to see the
behaviour of electron and positron, photon, neutron and muon fluences in a
spatial mesh: you will see the penetration of the different components of
the secondary radiation in the shielding wall and you could better
understand the results .

Hope it helps,
regards,

Anna

PS: the card RANDOMIZ is correct.

> Dear FLUKA users
>
> I've programmed an input with a simple geometry to score neutron and
> photon fluence but all the results got zero. please help me to find
> the problem.
>
> Thanks In Advance
>
Received on Wed Nov 10 2010 - 19:03:26 CET