From: Vasilis Vlachoudis (Vasilis.Vlachoudis@cern.ch)
Date: Tue Nov 06 2007 - 17:28:16 CET
the production cross sections for the Be(g,n) reaction is of the order
of 0.5-1mb (for typical photon energies of a few MeV) which means that
you are generating neutrons almost proportional with the thickness of
your target (r). On the other hand Be is fairly transparent to
low-energy neutrons as well to the beam photons, so the neutron
diffusion on your target will follow roughly 1/r^2. Therefore one should
expect a decrease of neutron fluence inverse proportional to the
dimension of the cube, while the total number of neutron generated per
second will be proportional to the dimensions of the cube.
You have to remember that the best quantity that one wants to optimize
in neutronic applications is the neutron fluence, since it is the one
defining the reaction rate.
Please give a look in the FLUKA courses especially the one on scoring
about the use of the existing estimators (for your case USRBDX,
USRTRACK, USRCOLL and USRYIELD) and how to interpret their results. Also
the output file of fluka in the last section provides valuable
information about secondaries yield, as well energy balance.
Mr. Bhushankumar Jagnnath Patil. wrote:
> Dear fluka experts and useres,
> In short my question is
> I want to set a geometry in fluka to calculate yield of ouptput particle
> from a cubical target. How to do it.
> I am studing gamma, n reaction on Beryllium target. I want to measure a
> neutron yield comming out from cubical shape of beryllium target. I am
> expecting that as the cube length increses the netron yield should
> increases and after certain length due to self absorption in the target
> the netron yield goes on decreses. So that i can optimised the target
> I have made a setup like this
> Gamma particle is comming on the a cube of Beryllium and i have measured a
> neutron flux comming out from the each surface of cube.
> The result for this shows me that as the cube length of Beryllium
> increses from 1 cm to 35 cm the neutron flux from each surface of target
> cube is going to decreases. But the number of neutron/sec is going to
> Also I have made one cube of air (cube length=40cm kept const) covering
> the beryllium target(varying cube length from 1 ro 35).
> The result for this shows me that as the cube length of Beryllium increses
> the total neutrons comming out from the bigger air cube is going to
> If my expection is correct then where i am making mistake?
> If my expection is wrong then what will be the result. ?
> If possible at least suggesest me the refereces to setup the model in
> fluka for study yield.
> Waiting for your favorable reply.
> Thanking you in an anticipation.
> Mr. Bhushankumar Jagnnath Patil.
> Research Student
> Microtron Accelerator Lab.
> Department of Physics,
> University of Pune,
> Ganeshkhind, Pune 411007
> Ph. No. Off. 020-25692678 Ext. 421
> Webpage http://physics.unipune.ernet.in/~bjp
> Alternate e-mail firstname.lastname@example.org
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