Re: Liquid scintillator efficiency

From: Vittorio Boccone <>
Date: Thu, 21 Feb 2013 00:22:55 +0100

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
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

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.


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
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Received on Thu Feb 21 2013 - 11:36:23 CET

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