Re: [fluka-discuss]: Simulation of coincidence summing effects in HPGe efficiency calibration

From: Santana, Mario <>
Date: Thu, 31 Mar 2016 17:44:29 +0000

Hi Andrea,

Maybe you could try to set GLOBAL card with what(2)<0 to make Fluka run
Œas analogue as possible¹.


On 3/30/16, 4:04 AM, " on behalf of Andrea
Mattera" < on behalf of> wrote:

>Dear Fluka experts,
>I am trying to simulate the detection efficiency of a HPGe; specifically
>we are interested in the coincidence summing effects if a source with
>multiple gamma lines is placed in close proximity of the detector. In
>order to do this I am using a BEAM ISOTOPE and the HI-PROPE cards to
>define a radioisotope as a source and I am detecting the energy in the
>HPGe using a (series of) DETECT [input file attached].
>We are comparing the Fluka simulation with measurements performed in
>very similar geometries and with the same sources (152Eu, 54Co, 133Ba):
>we could verify (see pag. 1 in the attached pdf) that the two efficiency
>curves agree very well over a wide energy range if we are in 'ideal'
>conditions (point-source placed at a relatively long distance to the
>source). This gave us some confidence that no big mistakes are there in
>the geometry and/or the scoring of particles.
>However, once we reduce the source-to-detector distance - i.e. when we
>expect the first effects of coincidence summing to appear - problems
>start to arise. Our simulation seems to largely over-estimate the
>effects of coincidence summing for most points (sometimes even by a
>factor of 3 or more, compared to the measurement) - see pag. 2.
>[OBS: another difference between the 'far point-source' vs 'close
>geometry' is that, in the latter case (both in measurement and
>simulations), the source is extended and mixed in concrete powder to
>account for self-absorption effects in the source]
>My first question to you is: is Fluka able to simulate these effects
>with the settings above in the input file (ISOTOPE + DETECT)?
>I would like to stress that we are not interested in (time-dependent)
>pile-up effects on the efficiency (the activity of the sources and hence
>the count-rate in our detector are very low). We only want to simulate
>coincidences coming from gamma cascades in the same decay event. From
>simple tests (e.g. with a 60Co source) it seems like Fluka shows a
>summing peak, which makes me hopeful that this is a good path to explore
>for our application [pag. 3].
>But: am I missing something in the physics or in the implementation? If
>our approach is in principle correct, do you have any guesses or hints
>at where we should look for an error that could explain the differences
>between simulation and measurements?
>Thanks a lot in advance for your help!

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Received on Thu Mar 31 2016 - 21:11:27 CEST

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