Dear Cristian,
As we discussed last time and as you observe when scoring on an event by
event basis (e.g. with EVENTBIN), for a monoenergetic neutron source <20MeV
you will get discrete energy deposition values, each corresponding to a
different nuclear species in your gas mixture.
If, as in your example, you detect 56 interactions, each depositing the
same value (e.g. 1 MeV) for a number of hitting primary neutrons Nprim,
then your reaction rate is of course 56/Nprim. This, however, does not tell
you what the real distribution of the energy deposition would be and so you
cannot tell how many would lie below a certain energy threshold relevant
for your detector.
This is very similar to a problem we encountered several years ago and was
addressed in the way I mentioned in my last reply, i.e. by a second
simulation generating e.g. recoil nuclei (HEAVYIONs) with appropriate
energy and angular distributions obtained from libraries (using the
recorded number of interactions in the first step to normalise to the
initial beam). Then you would get a full energy deposition spectrum. You
can find the relevant publication here, hoping it can provide some
inspiration:
http://www.sciencedirect.com/science/article/pii/S0168900212002446
Keep in mind that the method requires some custom processing of libraries
(ENDF) and a custom FLUKA source routine for the second step. It may be
somewhat impractical if you have to study many different beam energies, but
as far as I know, there is no other quick solution to your problem.
Best regards,
Andrea
P.S. As a small addendum, the number of interactions (e.g. 56) does not
correspond to a specific reaction channel but to all. One should look at
the corresponding cross-sections in ENDF and at the expected energy of the
corresponding secondary particles to see which may contribute more to the
energy deposition in the gas. E.g. will a recoil nucleus or a proton from
an (n,p) reaction be more important, or both? Are gammas important
(probably not in a thin gas detector)? etc... It could get messy depending
on the case, but if you can narrow down the problem to the most relevant
contributions, it can become manageable.
On Mon, Mar 27, 2017 at 9:17 AM, Cristian Antochi <
VasileCristian.Antochi_at_roma1.infn.it> wrote:
> Hello all,
> I am trying to estimate the interaction rate of low energy neutrons
> (~1-10MeV) in a gas target. Due to Kerma approximation the deposited energy
> doesn't give me an energy spectrum or a cut-off in order to estimate what
> could be the number of events seen by a possible detector but I have n
> interations with monochromatic deposition for example if I have a
> monochromatic beam. What I'm trying to say is, what is the energy threshold
> above which the interaction is registred?
> For example is there a way to say how many events will my detector see
> above 2KeV of deposited energy in a target where 56 low energy neutron
> interactions happen (monochromatic beam of 5MeV and monoenergetic mean
> kerma deposition of let's say 1MeV)?
>
> Thank you,
>
> Cristian Antochi
>
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Received on Mon Mar 27 2017 - 11:41:11 CEST