RE: [fluka-discuss]: FLOOD in BEAMPOSit

From: Anton Lechner <Anton.Lechner_at_cern.ch>
Date: Thu, 25 Sep 2014 14:19:57 +0000

Dear user,

I am not sure the FLOOD option is doing what you expect it to do. It is correct that photons are created homogeneously on the surface, but their direction is not pointing to the center of the sphere, but is isotropic (you say you want an isotropic source, but at the same time you say the photons should be pointing towards the sphere center, which is contradictory). Let me also quote the manual: "... such as to produce a uniform and isotropic fluence within the sphere.". Hence, no surprise that you don't see more photons in the bin close to the center.

Apart from that, it is no problem to set up particles in a material other than vacuum. However, as pointed out by Lefteris, the crash you encounter is indeed due to particles being set up on a region boundary by the FLOOD option (on the other hand, it should not be a problem to create source particles on a boundary when using for example the BEAM card).

Cheers, Anton



________________________________________
From: owner-fluka-discuss_at_mi.infn.it [owner-fluka-discuss_at_mi.infn.it] on behalf of Eleftherios Skordis [eleftherios.skordis_at_cern.ch]
Sent: 24 September 2014 09:41
To: akardeep_at_barc.gov.in; fluka-discuss_at_fluka.org
Subject: RE: [fluka-discuss]: FLOOD in BEAMPOSit

Greetings akardeep

As a good strategy it is advised to not have primary beam particles spawn directly at a boundary and much preferred to have them spawn in vacuum.
If you change the radius of the air sphere to be smaller by a micrometer (or your source to be a micrometer larger) [i.e. 100.0001 and 100 or 100 and 99.9999) you should not see problems any more.

Kind regards

Lefteris

-----------------------

Eleftherios Skordis
Dep. EN/STI, CERN
CH-1211 GENEVA 23
SWITZERLAND

OFFICE: +41-22-7679541

________________________________________
From: owner-fluka-discuss_at_mi.infn.it [owner-fluka-discuss_at_mi.infn.it] on behalf of akardeep_at_barc.gov.in [akardeep_at_barc.gov.in]
Sent: 24 September 2014 07:52
To: fluka-discuss_at_fluka.org
Subject: [fluka-discuss]: FLOOD in BEAMPOSit

I want to generate source points for photon emission, distributed
uniformly on a spherical surface. The direction of the emitted photons
should be directed inwards (preferably isotropic and directed towards the
center of the sphere).
I found FLOOD option along with extra BEAMPOSit card useful for this
purpose, as mentioned in the manual:
"for SDUM = FLOOD:
    the command defines a source distribution on a spherical surface, centred
    at the x,y,z point defined by another BEAMPOSit command with SDUM
blank or
    = NEGATIVE, such as to produce a uniform and isotropic fluence within the
    sphere. "

Using it, I made an input file and used USRBIN to score photons in a
parallelepiped passing through center and binned with 170 bins along
z-direction. (See attached flood.inp file).
My expectation was that more photons will be scored in the bin located
near the center of the sphere.
If I fill Water or lead inside VOID1, simulation runs fine. But if I
replace medium by air or any gas geometry error occurs. .out and .err
files are also attached with this email.
Please help me to resolve the problem.
Received on Thu Sep 25 2014 - 17:41:12 CEST