Monte Carlo simulation of liquid scintillation neutron detectors:

BC501 vs. BC537

J.L. Taintain@ific.uv.es

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

C6D6 detectors at n_TOF-CERN

(n,n)

(n,)

1keV 1MeV

BC501 BC537

En=2.5MeV

En=4.3MeV

From S. Williams (TRIUMF) : (@ Warsaw, Oct 2007)DESCANT: DEuterated SCintillator Array for Neutron Tagging

Motivation:

102.5cm

!?

BC501/NE213 liquid scintillators

Mono-energetic neutron response

C1H1.212

= 0.874g/cm3

n (@425nm) = 1.53 = 3.2 (32.3, 270) ns

5cm5cm

NIMA476 (02) 132

255cm

Neutron scattering

s-wave (l=0) elastic scattering:

A

n

min

There is a minimum neutron energy (maximum recoil energy) after the collision, A dependent:

Isotropic in CMS:

Energy-momentum conservation:

1-: H (1.0), D(0.89), C(0.28), Fe(0.069), Pb(0.019)

ELASTIC SCATTERING ANGULAR DISTRIBUTION

1H 2H

12C 208Pb

CM system

Angular distribution in the LAB reference frame

1H

2H

En = 1MeV

En = 5.5MeV

Monte Carlo simulations of liquid scintillation neutron detectors

• General purpose codes: GEANT3, Geant4,… and specific codes: NRESP, SCINFUL, …

• Requires nuclear reaction data (missing information on 12C(n,n3), …)

• Requires material response (light production, …)

ENDF/B-VII.0

Luminescence in organic materials

Several time components

The non-radiative transfer mechanism between excited centers induces an energy-loss dependent light production …

dxdE

kB

dxdE

S

dx

dL

1… and a varying time distribution

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

Light production curves:

(In reality there is some dependence on chemical composition, fabrication, age, …)

EELELL (assumed same and 12C light curves in BC501 & BC537)

(10x10cm)

“ENERGY CALIBRATION”

Neutron interaction time

t=5ns:C6D6: 98.3%BC501: 95.6%

CONCLUSION: !?

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

En15cm15c

mMULT 1 MULT 2 MULT 3 M2/M1

1 MeVBC501 76.4% 15.5% 0.5% 20.3%

C6D6 69.3% 12.5% 0.24% 18.1%

5 MeVBC501 49.5% 22.3% 2.3% 45.2%

C6D6 45.3% 18.6% 2.4% 41.1%

En = 1 MeV En = 5 MeV

Eth=100keV

En 5cm15cm MULT 1 MULT 2 MULT 3 M2/M1

1 MeVBC501 61.5% 5.1% 0.1% 8.28%

C6D6 44.1% 3.9% 0.04% 8.87%

5 MeVBC501 31.8% 3.6% 0.2% 11.35%

C6D6 27.1% 2.9% 0.15% 10.55%

En = 1 MeV En = 5 MeV

Eth=100keV

En

15cm15cm

BC501 C6D6

1 MeV 2.8% 5.6%

5 MeV 6.3% 10.4%

Ratio of counts scattered to outer detectors respect to central detector in the energy window [Emax/2,Emax]

En

5cm15cm

BC501 C6D6

1 MeV 1.4% 2.5%

5 MeV 2.6% 3.5%

En = 1 MeV En = 5 MeV15cm15cm

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