Re: Liquid scintillator efficiency

From: Vittorio Boccone <>
Date: Fri, 1 Mar 2013 15:54:34 +0100

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Dear Beatrice,

On 02/25/2013 10:28 AM, Beatrice Pomaro wrote:
> gives a procedure to compute the scintillator efficiency, however I am
> not sure I have well understood: the so called 'absolute detector
> efficiency' for a specific neutron energy is computed as the ratio
> between the integral over the proton energy of the response function
> expressed in number of recoiling protons and the monochromatic
> incident neutron fluence. The dimension for this quantity is cm2.
I would say that this is the "intrinsic" detector efficiency not the
absolute. What you mention is the ratio that express the efficiency of
generating recoiling protons i.e. how many recoiling protons per
impinging neutron and depends only on the physics (cross section
material, dimensions) and not on the detector and background you might have.

> But which are the scoring card necessary in Fluka to enable this
> computation? I thought I needed a USRTRCK for protons to be integrated
> over the proton energy in order to have the recoiling
> protons/primary/cm2, in the assumption that up to a few MeV neutron
> energy only the recoil protons can be taken into account. However I do
> not reach realistic values for the detector efficiency and above all
> mine turns to be expressed into protons/primary/cm2; how can I have a
> non-dimesnional quantity out of it, as efficiency should be conceived,
> ranging from 0 to 1.
If you want to simply count the total number of generated proton recoil
(and their energy) and do a spectral analysis of your results I would
probably use the USERDUMP card toghether with an ad-hoc mgdraw.f user
routine and the do a bit of off-analysis line analysis afterwards.

> Thank you in advance,
> Sincerely,
> Beatrice
> Il 21-02-2013 00:22 Vittorio Boccone ha scritto:
>> Dear Beatrice,
>> the efficiency of a liquid scintillator detector depends on many factors.
>> The BC501a is not only a neutron detector but is also very sensitive to
>> gamma (and electrons) and allows pulse shape discrimination by
>> evaluating the ratio between the population of the different decay
>> components. If you have some neutron shielding around the neutron source
>> the gamma component might not be negligible.
>> The ratio of recoiling protons (only) divided by the number of neutron
>> will not represent the efficiency of your detector but only the average
>> number of protons recoils produced and you will neglect the the other
>> components. Your proton spectrum is already normalized per primary
>> particle so the integral will give you a the total energy deposited by
>> the protons per primary.
>> When you convert the proton spectrum in MeVee (presumably with the
>> empirical formula given by the Saint-Gobain) you just express the
>> response to protons in an "equivalent" electron response. To link this
>> number the actual quantity of photons detected by your device you need
>> to make assumption on the scintillation yield (for the BC501a it's given
>> with respect to Antracene), on the light collection efficiency of your
>> device
>> and on the detector (PMT or other) efficiency.
>> So if you are interested in simulating the scintillation light yield you
>> probably have to enable the production of the scintillation photons
>> (OPT-PROD) but you have also to set all the relevant parameters and
>> optical properties of the material (refraction index, absorption
>> coefficient ... ). Normally those type of detectors have a light yield
>> of 1.5-2 p.e./keVee, the correct value is normally determined
>> empirically as it requires the precise knowledge of many different
>> parameters.
>> I can't tell you if your thresholds are correct or not (it depends on
>> what exactly you want to measure). They look a bit high, but again it
>> depends on what you need to determine. I would anyway start from the
>> PRECISIOn default and set the EMFCUT down to values below your required
>> threshold in the BC501a.
>> Best
>> Vittorio
>> On 20/02/2013 10:03, beatrice pomaro wrote:
>>> Dear Fluka experts, I am analyzing the efficiency of a neutron
>>> scintillator; I consider several energies of the neutron beam
>>> against the detector, then score the proton spectrum at the region
>>> of the detector and convert it into light output (MeVee); at this
>>> step how can I proceed to calculate the detector efficiency? Is it
>>> correct to compute it as number of neutrons from the initial beam
>>> divided by number of protons (integral of the spectrum for the
>>> specific neutron energy). If this is true, how can I know the
>>> numerator from the simulations? I provide my input file in
>>> attachement and ask also if , for this problem, the input cards
>>> NEWDEFA and EMFCUT are the proper ones. Thank you for your
>>> attention, Sincerely, Beatrice
>>> ************************************************** Ing. Beatrice
>>> Pomaro Universita' degli Studi di Padova Dipartimento di Ingegneria
>>> Civile, Edile e Ambientale Via F. Marzolo, 9 - 35131 Padova (Italy)
>>> tel.: +39 049 8275605 e-mail:
>>> <>
>> --
>> Dr. Vittorio Boccone - University of Geneva
>> o Address:
>> UniGe: Département de physique nucléaire et corpusculaire
>> 24 Quai Ernest-Ansermet, CH-1211 Geneve 4, Switzerland
>> CERN: CERN, CH-1211 Geneve 23, Switzerland
>> o E-mail:
>> <>
>> <>
>> o Phone:
>> Mobile: +41 76 487 5737
>> UniGe: +41 22 379 6357/6353
>> CERN: +41 22 767 5821
> --
> **************************************************
> Ing. Beatrice Pomaro
> Universita' degli Studi di Padova
> Dipartimento di Ingegneria Civile, Edile e Ambientale
> Via F. Marzolo, 9 - 35131 Padova (Italy)
> tel.: +39 049 8275605
> e-mail:
Received on Fri Mar 01 2013 - 17:07:30 CET

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