Transcript Investigation of Tetrahedral Symmetry in Nuclei

“Universa Universis Patavina Libertas”
LIGHT-OUTPUT SIMULATIONS
FOR NEDA
Andrea Gottardo
Università di Padova
18/07/2015
NEDA meeting
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Plan of presentation
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Introduction : The importance of light-output
response in scintillators
Calculations for light-output produced by neutrons
Light-output spectra
First estimations of efficiency and cross-talk for
NEDA
Conclusions
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Light-output response: why?
The light-output response of a scintillator has to be addressed carefully
when estimating the efficiency or the cross-talk effect
In fact, the actual signal intensity from a PMT depends on the lightoutput.
Scintillator
PMT
light
Neutron
charge
electronics
Neutrons with the same energy do not always produce the same light
output, i.e. the same signal intensity
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Scintillator light response
• The energy of the particle(s) scattered by
collisions with the incoming neutrons
• The kind of the particle(s) scattered by
collisions with the incoming neutrons
The light-response
depends on:
• Other characteristics of the scintillator
such as the optical coupling to the PMT,
the light transport and reflection in the
scintillator itself…
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Light-output importance for NEDA
Simulation for neutron detector
Realistic estimation
of the intensity of
output signals
J. Ljungvall et al., NIM
A 528 (2004), 741.
The final goal is to obtain a credible evaluation of some key
parameters such as efficiency and cross talk
NEDA as multiplicity filter to select n-rich reaction channels
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Light-output definition
The light-output L is usually given in MeVee: the particle energy required to
generate 1 MeVee of light is defined as 1 MeV for fast electrons
Light: 1MeVee
e- @ 1 MeV
PMT
e- range
L is generally less for heavier particles such as protons, deuterons, alphas,
beryllium, carbon…
Therefore, the light output L in a certain path dx is a function of the
deposited energy E in dx: L(E)
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Light-output estimation
dL
 dE 
 dE 
 dE 
 S
1  kB
  C

dx
 dx 
 dx 
 dx 
The Birks-Chou formula provides
a theoretical description of the
light emission
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



1
However, an easier phenomenological formula is also available
ΔL = light output of the particle
scattered by a neutron in a single ith
step of its stopping process
L   Li
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i
E - ΔE
E
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Light output parametrization (1)
Dekempeneer et Liskien
NIM A 256 (1987) 489-498: NE213
The light-output function provided
for protons is a polynomial one
(3rd order ) :
LP(E)=A0+A1E+A2E2+A3E3
Carbon, Boron: L(E) = 0.0097 E
Deuteron: L(E) = 2 Lp(E/2)
Be: L(E) = 0.013E
Alpha: L(E) =
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•0.0201E1.871
E < 6.76 MeV
•-0.6278+0.1994 E E ≥ 6.76 MeV
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Light output parametrization (2)
Many parameterizations exist in literature, also for energies above 16 MeV.
R.A. Cecil et al. NIM 161 (1979) 439-447, for example
N.P. Hawks et al., NIM A 476
(2002) 190
D. Cano-Ott and
collaborators, private comm.
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Light output parametrization (3)
µ = 0.045
Gaussian resolution for L
FWMH  μ 2 L2 + β 2 L + Y 2
H. Schölermann and H. Klein, NIM 169 (1980), 25
β = 0.075
Y = 0.002
The resolution describes:
1. Light transmission from different points (µ)
2. Statistical effects on light production (β)
3. Noise (Y)
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Light output for 10 MeV neutrons
(electrons)
Deposited energy
10* keV
16/06/2009
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Light output
10 * keVee
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Light output for 10 MeV neutrons
(protons)
Deposited energy
10 * keV
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Light output
10 * keVee
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Light output for 10 MeV neutrons
(carbon)
Deposited energy
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10 * keV
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Light output
10 * keVee
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Light output for 10 MeV neutrons
12
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4
(alphas from C+n-> Be+ He)
Deposited energy
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10 * keV
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Light output
10 * keVee
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Light output for 10 MeV neutrons
9
12
9
4
( Be from C+n-> Be+ He)
Deposited energy
10 * keV
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Light output
10 * keVee
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Light output for 10 MeV neutrons
(deuterons)
Deposited energy
10 * keV
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Light output
10 * keVee
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Light output for 10 MeV neutrons
(all)
Deposited energy
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10 * keV
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Light output
10 * keVee
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Efficiency
The efficiency of the NEDA prototype is calculated for an emission at 1m
distance with an angular aperture of θ =14°
θ
Tayfun Huyuk,
source
private comm.
1m
The efficiency has been calculated for 4 different thresholds as:
N 1
eff 
N sent
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Efficiency: results
1 MeV n
Threshold
(MeVee)
Efficiency
%
0
74.6
0.25
6.5
0.50
6.0
0.75
5.5
0.75
0.50
0.25
10 keVee
8 MeV n
Threshold
(MeVee)
Efficiency
%
0
63.6
0.25
40.1
0.50
36.2
0.75
33.1
0.25
0.75
0.50
10 keVee
16/06/2009
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NEDA meeting
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Cross talk
n'
Cross talk: the same neutron can be
scattered and detected among different
scintillators
Cross talk:
N  2 hits
N1hit
Tayfun Huyuk,
n
private comm.
We calculated it for 19 detectors, in the same conditions as the efficiency
simulation
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Cross talk: results
1 MeV n
Threshold
(MeVee)
Cross talk
%
0
46.8
0.25
16.2
0.50
8.7
0.75
3.8
8 MeV n
Threshold
(MeVee)
Cross talk
%
0
39.4
0.25
17.6
0.50
12.0
0.75
8.3
0.75
0.50
0.25
10 keVee
0.25
0.75
0.50
10 keVee
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Conclusions and open problems
We have implemented in Narray code the calculations for the light
output of a scintillator, considering the different kinds of recoils
involved.
HOWEVER…
1. What parameterization to be used?
Several available, situation more confused
for energies above 16 MeV
2. Is the light-output really a universal function?
3. Need to test the scintillator to validate simulations?
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Light output for 10 MeV neutrons
(photons)
Deposited energy
16/06/2009
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10 keV
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Light output
10 keVee
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