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

From: Andrea Mattera <>
Date: Thu, 31 Mar 2016 21:19:58 +0200

Hi Mario,

thanks for your reply!

I think I do already have a GLOBAL set to negative (in Flair I select
the drop-down menu as 'Analogue' that sets a value to -1. - which I
assume is what(2)?). Is the card 'position sensitive'? Right now it is
in the very first line of my input file: should I perhaps move it
somewhere else?



On 03/31/2016 07:44 PM, Santana, Mario wrote:
> Hi Andrea,
> Maybe you could try to set GLOBAL card with what(2)<0 to make Fluka run
> Œas analogue as possibleš.
> -Mario
> 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!
>> /Andrea

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Received on Thu Mar 31 2016 - 22:44:50 CEST

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