Average energy of spallation neutron source

Dear Fluka experts,
After the flair gives .out file, it shows the n/p in the summary tab. However, average energy seems not shown in this section. It needed to be calculated by the user? or is there somewhere else to find these values (average energy and Fraction of high-energy neutrons)?

Dear @thanapong,

Thanks for your question.

As you said, you can obtain the neutron yield (neutron per primary) in the .out in the section:
“Number of secondaries generated in inelastic interaction per particle”.
Of course, It is only in the case that all your interactions are in one region (in your case, the material for the spallation)

In the cases of average energy of neutrons generated and fraction of high-energy neutrons, there is no way to obtain them from the .out file.

My suggestion to you is to use an extra scoring to obtain the yield of neutrons, and with this results you could calculate them.
You could obtain the three values using USRYIELD, using the EMERGING option, where you obtain “yields of particle emerging from inelastic hadronic interactions with single nuclei”.
An example of how you should use this card is shown here:

Here you see that we use the quantities of kinetic energy and particle charge.
We defined explicitely that we want to score NEUTRONS in the input, but USRYIELD scores double-differential yield, then we had to use also the particle charge as a quantity, giving the range or -0.5 to 0.5.
You should just fill the range of energies of your problem.

Finally you will obtain an spectrum where you can calculate by yourself the neutron yield, average energy and fraction of high-energy neutrons.

Let me know if it’s clear, otherwise we can keep discussing.

Best.
André

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Thank you for your kind information. May I ask a little bit more about getting the spectrum to calculate the neutron yield, average energy, and fraction of high-energy neutrons. Is it in the .out file or do I need to obtain the result from .lis file by using usysuw ?.

Dear @thanapong,

What you say is correct.
But in case your are using Flair for your simulations,
in the process of merging your results, what you are actually doing is
using the routine USYSUW.
This routine merges the results and gives you 3 outputs (MANUAL, Note 13):

tab.lis, sum.lis)

        It returns differential and cumulative fluence,
        with the corresponding percent errors, in a file, and differential
        fluence in another file formatted for easy plotting.

.yie)

        It also returns a binary file that can be read out in turn by USYSUW. 

As a quick check of your results, you can compare the results of neutron yield in
sum.lis → “Tot. response (integrated over x1)”
The value obtained should be similar to the one you see in the .out files.

To conclude… yes, you have to use USYSUW to obtain the tab.lis and sum.lis
from where you can calculate by yourself the three results that you are looking for,
but these files are obtained automatically in the process of merging the results.

I hope this can help you,
Cheers,

André

@adonadon Thank you so much, I will try on it.

One more question about .out file. If I want the number of low energy neutron yield, I have to see at the column “number of secondaries created by low energy neutron per beam” right? and What is the meaning of neutron and fission neutron in that column?

Thanks in advance.

Dear @thanapon,

Sorry for the delay in replying.

  1. If I want the number of low energy neutron yield, I have to see at the column “number of secondaries created by low energy neutron per beam” right?

That’s correct, BUT what you are getting there is the number of low energy neutrons generated from the reinteractions of low energy neutron. Is this what you are looking for?

In order to define properly what you need, it’s important to define the following:

Are you interested in neutron production by proton spallation reactions or do you want to include also neutron reinteractions?

Answering this question will allow use to properly define what we want to score and how to do it.
Let me know.

  1. What is the meaning of neutron and fission neutron in that column?

Fission neutron in that column means ‘neutrons generated in fissions induced by low energy neutrons’.
A bit info in the manual

Cheers,
Have a nice weekend

André

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Dear @adonadon ,

Thank you for your explanation.

I’m interested in neutron production by proton spallation reactions.

Have a nice day,
Thanapong

Dear @thanapong,

Perfect. Then, my recommendation is to use the USRYIELD card discussed above, and in order to get only the neutron production by proton spallation reactions, you should define a thin target ( <= Inelastic scattering length).

Doing this you will get what you are looking for.

Extra comment: In case you don’t know the scattering length just doing a simple run with 1 particle you can obtain it from the .out file.

Let me know if it has sense for you.
Have a nice day,

André