Re: variation of efficiency with energy in BC 501A

From: Vittorio Boccone <Vittorio.Boccone_at_cern.ch>
Date: Thu, 1 Aug 2013 23:01:26 +0000

Dear Saneesh,
  in BC 501 the light output produced by the recoiling proton is not only proportional to the released energy.

In my opinion you should a plot which

As you probably know those scintillator are used to perform particle identification because they have different light yield for different particles, and the conversion between
the response of protons and electron (give by St.Gobain)is E~0.83*P - 2.82 [1-exp(-0.25*P^{0.93})] where P is the proton energy and E is the equivalent electron energy (both in MeV)

The energy of the proton recoils depends on the energy of the impinging neutron and it’s scattering angle. For elastic collisions the energy of the recoiling proton should be something like Ep=En (1-cos^2 theta). The recoiling proton will generate ionise and excite the atoms around. Depending on the energy of the recoiling proton part of the light production will be quenched due to the high ionization density of stopping proton. With FLUKA you can score the energy scaled by a quenching factor (Birk Law), but this is normally interesting only at low energies.

You only mention protons, you neglect that for larger energy Carbon has also a non negligible effect.

Another effect (more important) is that the real efficiency of your detector is determined by shape and the goodness of your light collectors (and reflectors) as well as the efficiency of your detector which often very complicate to model correctly.


P.S. Check out this master thesis
https://www.maxlab.lu.se/sites/default/files/karlsson2.pdf

P.P.S Just a suggestion: keep the material ID of the MATERIAL card empty (unless you really need it), so FLUKA will get you the next free one.

Best
V.
-- 
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:
  vittorio.boccone_at_unige.ch
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On 30 Jul 2013, at 14:37, saneesh_at_iuac.res.in wrote:
> Dear Fluka experts,
>                   I am trying to simulate the variation of efficiency with
> energy, for neutrons, in organic liquid scintillator BC
> 501A. Since the light output is proportional to the
> energy deposited by recoil protons, the variation of
> energy  deposited by recoil proton with neutron energy
> is expected to produce identical result. The result
> obtained is given below.
> Neutron energy (MeV)    Recoil proton energy (MeV)
> 0.5                       0.227
> 1.0                       0.468
> 2.0                       0.731
> 3.0                       0.905
> 4.0                       1.031
> 5.0                       1.163
> 6.0                       1.237
> 7.0                       1.310
> 8.0                       1.339
> 9.0                       1.385
> 10.0                      1.421
> 12.0                      1.480
> 14.0                      1.514
> 16.0                      1.502
> 18.0                      1.497
> 20.0                      1.576
> 25.0                      1.491
> 30.0                      1.554
> 
>      The result shows that efficiency saturates near 15 MeV. I have
> compared with the results of M.Drosg, NIM 105(1972) 573 (please find
> the attachments). Unlike my results, there is always a reduction in
> efficiency with energy >10MeV. And also I couldn't find a way to set
> the production threshold of secondary protons. I am attaching one of
> the input file along with mail (successive simulations are done by
> varying the energy only). Please help me to resolve the problems.
> 
> Thanks in advance
> 
> Saneesh N
> 
> 
> <P_recoil.inp><Efficiency_vs energy1.jpeg>
Received on Fri Aug 02 2013 - 09:36:41 CEST

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