RE: [fluka-discuss]: Thermal neutron fluence using USRBDX scoring

From: Georgios Tsiledakis <>
Date: Thu, 16 Apr 2015 09:17:25 +0000

Dear Sunil,

Thank you very much for your answer...
I have tested what you proposed and its true that the beam particles dont hit the Cobalt target...
But since they are thermal neutrons, no matter how they are emitting from the beam, inside Water they should create a kind of thermal neutron gas travelling in all directions and finally hit the thin target...
My logic was that the presence of Germanium cylinder inside the Water volume should absorb many neutrons, resulting at a measured neutron fluence in the target smaller than the one without the presence of Germanium...
What I measured with high statistics was just the one way scoring of neutrons from Water towards Cobalt. Surprisingly, the results are the opposite I was expecting...
Is any mistake considering my DEFAULTs settings or any more appropriate PHYSIC card that could be used?

Thank you very much in advance

Best regards

From: Sunil C []
Sent: 13 April 2015 07:35
To: Georgios Tsiledakis
Subject: Re: [fluka-discuss]: Thermal neutron fluence using USRBDX scoring

Dear Georgios

I see that your beam is directed towards the positive Z, while your Co is somewhere in the -Y half. Thus the beam is not going anywhere near your cobalt. If you plot a USRBIN data containing the beam particles, you can see that this is indeed the case. I have attached such a plot. The difference in your 2 plots or the numbers you report do not seem to be very much and I suspect is due to statistical fluctuations. With 14-18% uncertainty, I will be very cautious with any conclusion.

Change your beam direction to point towards the -Y region and try.

Cheers Sunil

On Fri, Apr 10, 2015 at 4:19 PM, Georgios Tsiledakis <<>> wrote:
Dear fluka experts,

I have a cylinder of H2O and a beam of thermal neutrons that hits on it...
Inside the water cylinder there is a small thin box made of Cobalt (target) which
is next to a Germanium cylinder...
Using USRBDX scoring -one way- , I would like to demonstrate that the flux of neutrons from H20
that hit the Cobalt target is smaller with the presence of the germanium cylinder.

But the results as you can see at the attached picture are the opposite...

Why is that?

Is any other way to conclude concerning the effect of Ge in the neutron flux on the Co target?

Thanks a lot in advance

Best regards


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Received on Thu Apr 16 2015 - 12:44:32 CEST

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