Monte Carlo simulation of liquid
scintillation neutron detectors:
BC501 vs. BC537
J.L. Tain
[email protected]
Instituto de Física Corpuscular
C.S.I.C - Univ. Valencia
BC537 as low neutron sensitivity -ray detector
State of the art detectors for (n,)
measurements using the Pulse
Height Weighting Technique at
time-of-flight facilities
(n,n)
1keV
1MeV
(n,)
C6D6
detectors at
n_TOF-CERN
Motivation:
BC501
BC537
En=2.5MeV
102.5cm
!?
En=4.3MeV
From S. Williams (TRIUMF) : (@ Warsaw, Oct 2007)
DESCANT: DEuterated SCintillator Array for Neutron Tagging
BC501/NE213
liquid
scintillators
5cm5cm
C1H1.212
 = 0.874g/cm3
n (@425nm) = 1.53
 = 3.2 (32.3, 270) ns
NIMA476 (02) 132
Mono-energetic neutron response
255cm
Neutron scattering
s-wave (l=0) elastic scattering:
Energy-momentum
conservation:
n
A
Isotropic in CMS:
There is a minimum neutron energy
(maximum recoil energy) after the
collision, A dependent:
min
1-: H (1.0), D(0.89), C(0.28), Fe(0.069), Pb(0.019)
1H
2H
CM system
ELASTIC SCATTERING ANGULAR DISTRIBUTION
12C
208Pb
Angular distribution
in the LAB
reference frame
1H
En = 1MeV
2H
En = 5.5MeV
Monte Carlo simulations of liquid scintillation
neutron detectors
ENDF/B-VII.0
• Requires nuclear reaction data
(missing information on 12C(n,n3), …)
• Requires material response (light
production, …)
• General purpose codes:
GEANT3, Geant4,… and
specific codes: NRESP,
SCINFUL, …
Luminescence in organic
materials
The non-radiative transfer mechanism
between excited centers induces an
energy-loss dependent light production …
dE
dL
dx

dx 1  kB dE
dx
S
… and a varying time distribution
Several time
components
Light production curves:
p, , 12C in NE213: Dekempeneer
et al. NIM A256 (1987) 489
d in NE230: Croft et al. NIM A316
(1992) 324
Simulations with
GEANT3/GCALOR 
(In reality there is some
dependence on chemical
composition, fabrication, age, …)
L  LE   LE  E 
(assumed same  and 12C light
curves in BC501 & BC537)
(10x10cm)
“ENERGY CALIBRATION”
CONCLUSION: !?
Neutron interaction time
t=5ns:
C6D6: 98.3%
BC501: 95.6%
C6D6 =12.2%
BC501=17.7%
(Eth=100keVee)
Does the use of C6D6 diminishes the cross-talk?
Simulation:
• cluster of 7 hexagonal
detectors
• diameter: 15 cm
• length: 5 cm and 15 cm
• maximal illumination of
central detector
• source at 1 m
• neutron energies: 1 MeV
and 5 MeV
En
15cm15cm
MULT 1
MULT 2
MULT 3
M2/M1
BC501
76.4%
15.5%
0.5%
20.3%
C6D6
69.3%
12.5%
0.24%
18.1%
BC501
49.5%
22.3%
2.3%
45.2%
C6D6
45.3%
18.6%
2.4%
41.1%
1 MeV
5 MeV
En = 1 MeV
En = 5 MeV
Eth=100keV
En
5cm15cm
MULT 1
MULT 2
MULT 3
M2/M1
BC501
61.5%
5.1%
0.1%
8.28%
C6D6
44.1%
3.9%
0.04%
8.87%
BC501
31.8%
3.6%
0.2%
11.35%
C6D6
27.1%
2.9%
0.15%
10.55%
1 MeV
5 MeV
En = 1 MeV
En = 5 MeV
Eth=100keV
Ratio of counts scattered to outer detectors respect to
central detector in the energy window [Emax/2,Emax]
15cm15cm
En = 1
MeV
5cm15cm
En
BC501
C6D6
1 MeV
1.4%
2.5%
5 MeV
2.6%
3.5%
En = 5 MeV
15cm15cm
En
BC501
C6D6
1 MeV
2.8%
5.6%
5 MeV
6.3%
10.4%
Conclusion:
The use of deuterated scintillators does not seem to
represent an advantage with respect to hydrogenated
scintillators in order to reduce the inter-module neutron
scattering