Mikhail,
one must be careful to not confuse 3 different things: an isotropic point source, an
isotropic source uniformly distributed in a volume, and an isotropic fluence.
1) An isotropic point source emits radiation in all directions with the same intensity.
To define it, use command BEAM with WHAT(3) (divergence) > 2000 x PI mrad.
2) An isotropic source uniformly distributed in a volume can be defined with
command BEAMPOS and SDUM=SPHE-VOL (if the volume is a sphere or a spherical
shell) or CYLI-VOL (if the volume is a cylinder or a cylindrical shell), or CART-VOL
(if the volume is a parallelepiped or a Cartesian shell). In all these cases, the isotropy
of the source is obtained with a command BEAM with WHAT(3) > 2000 x PI mrad'
as in case 1).
3) An isotropic fluence is a very different thing: a volume containing particle tracks
oriented in all directions with the same probability. What you wrote:
> To implement an isotropic, uniform point-like (sphere with very small
> radius) source use BEAMPOS card with type FLOOD. Another BEAMPOS card
> set the position of the source.
is incorrect. BEAMPOS with SDUM=FLOOD does not describe a point-like source,
but a source distributed on a spherical surface, such that it produces an isotropic
and uniform FLUENCE inside the sphere. A second command BEAMPOS with SDUM
blank is necessary to define the centre of the sphere (NOT the position of the source,
which is distributed on the surface of the sphere, and does not emit particles
isotropically, but with a cosine distribution).
Alberto
________________________________________
From: owner-fluka-discuss_at_mi.infn.it <owner-fluka-discuss_at_mi.infn.it> on behalf of Mikhail Polkovnikov <νΙΘΑΙΜ πΟΜΛΟΧΞΙΛΟΧ> <pmk_at_ihep.ru>
Sent: Thursday, August 20, 2015 2:55 AM
To: teterev; fluka-discuss_at_fluka.org
Subject: Re: [fluka-discuss]: BEO
On 20.08.2015 10:45, teterev wrote:
> Hello!
> Can I calculate the number of emitted neutrons by using Fluka, if the
> source of neutron is located in the middle and around it located BEO?
> I do not know how to build the geometry, if it is possible to make
> this calculation, how to determine the neutron source? Set in the
> middle of a neutron as BEAMPOS? And can I calculated the neutron yield
> around BEO by using USRYIELD?
> Thank you very much!!!
To implement an isotropic, uniform point-like (sphere with very small
radius) source use BEAMPOS card with type FLOOD. Another BEAMPOS card
set the position of the source.
*...+....1....+....2....+....3....+....4....+....5....+....6....+....7....+....
BEAM -0.001 -1.0NEUTRON
BEAMPOS 0.0 0.0 0.0
BEAMPOS 0.0001 0.0 0.0 FLOOD
Best regards,
Mikhail
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Received on Thu Aug 20 2015 - 16:25:46 CEST