Re: Re: [fluka-discuss]: I: 18 MeV Neutrons on Carbon

From: Fasso, Alberto <>
Date: Thu, 16 Jul 2015 10:25:34 +0000

Dear Francesca,

there is one big issue in your input file (I confess that I have not even looked at the mgdraw routine, maybe I will have a look later).

In your LAM-BIAS command, you have set a biasing factor of 5.0E-12: that means that you have increased the cross section by a factor 2.E11!!!

If you look at the carbon cross section for 18 MeV neutrons, for instance on the Brookhaven NNDC site, you find that the total cross section

is about 1.4 b, and the inelastic cross section about 10 times lower. That means that if you set the biasing factor = 1.E-2 you have already

a 99% probability that the neutron will interact within the 5 mm of your target. That should be more than enough! Maybe you could even bias

a little less, say a biasing factor 0.05.

I did not find any other problem in your input file, but perhaps you could consider the following:

* I suggest that you could use DEFAULT PRECISION instead of NEW-DEFA

* command LOW-NEUT is not necessary. Everything is already there by default

* in the MATERIAL definitions, don't type the mass number (leave WHAT(2) blank). FLUKA has its own table of mass numbers and it is better not

   to interfere

* just a curiosity: why have you biased also the antineutrons? Do you expect any?

* you must be an old "customer", since in most of your input you use numbers instead of names. That was the way we used FLUKA many years

   ago, but now I have lost the habit and have had myself some difficulty in understanding your input. Try the names! They will make your life

   much easier :-)

Kind regards,


From: <>
Sent: Thursday, July 16, 2015 1:45 AM
To: Fasso, Alberto;
Subject: R: Re: [fluka-discuss]: I: 18 MeV Neutrons on Carbon

Dear Alberto,

         I apologize for sending files this way. The browser I use at work is preventing me to attach files, and I
am not allowed to make any change on the computer I am using.

I had interfaced the FLUKA output with ROOT because I am terrible in one
command line I insert 5 mistakes :)

A TFile is practically a folder and a TTree is a way to store data, like ntuple.
But you are right that the TTRee is not necesary (in my case it is even empty...).

I cleaned the input and put test.inp and mgdraw.f at the follwoing link

If i use instead than 18 MeV neutron, 0.1 GeV neutrons I obtain also residual nuclei....
Is the fact that I obtain practically nothing with 18 MeV neutrons linked to the low energy neutron treatment, please?
Or do i make some other basic mistake, please?

Thanks a lot,

----Messaggio originale----
Data: 16/07/2015 10.19
A: ""<>, ""<>
Ogg: Re: [fluka-discuss]: I: 18 MeV Neutrons on Carbon

Dear Francesca,

please forgive a Paleolithic person...

1) What is a TTree? I looked it up on Google and it looks that it is something to do with ROOT. But please consider that not everybody is using ROOT! In particular,

it is not necessary to know ROOT for using FLUKA

2) I had a look at the link you sent, and I was able to download the following:

NeutCarb.tar.gz_files/ (a directory)


The stuff seems to gzipped, but the .gz is an extension in the middle of the file (or directory) name. How does one gunzip them?

The bottom line is: can you please provide input file and user routines in a less sophisticated way, if you want to be helped by Paleolithic people? :-):-):-)

Just two simple ASCII files would be ok...


From: <> on behalf of <>
Sent: Wednesday, July 15, 2015 11:29 AM
Subject: [fluka-discuss]: I: 18 MeV Neutrons on Carbon

Dear all,

     I made a mistake. The link is


----Messaggio originale----
Data: 15/07/2015 19.35
A: <>
Ogg: 18 MeV Neutrons on Carbon

Dear all,

           I am trying to simulate the response of a diamond detector to a monochromatic pencil-like neutron beam.
I was expecting different reactions to take place and, as a consequence, to be able to score with mgdraw the
energy deposited by charged particles, for example alphas, in the carbon.

But I must be doing something completely wrong, since the energy deposited in the diamond is always 0
(not to get a large TTree for nothing, in the mgdraw routine I asked to dump the energy deposited only if it is higher than 0.
As a cosnequence nothing is written on the TTree).

To understand what'sgoing on, I edited also usdraw by following
and dump the results on the *.log file.
But I get always only neutrons.

I have problems in attaching files using the browser at work, therefore I uploaded the simulation at the link
(this time everyone should have direct access, at least for the download).

Could anyone give a look please?



To run the simulation:

-expand the file in a folder
-add to your .bashrc
        export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/folder_where_you_put_the_simulation
-source .bashrc
-digit make
-digit $FLUPRO/flutil/rfluka -e rootfluka -N0 -M5 test &

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Received on Thu Jul 16 2015 - 13:51:21 CEST

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