Monte Carlo simulation of liquid scintillation neutron detectors: BC501 vs. BC537 J.L. Tain 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

BC501BC537 E n =2.5MeV E n =4.3MeV From S. Williams (TRIUMF) : Warsaw, Oct 2007) DESCANT: DEuterated SCintillator Array for Neutron Tagging Motivation: 10  2.5cm !?

BC501/NE213 liquid scintillators Mono-energetic neutron response C 1 H  = 0.874g/cm 3 n = 1.53  = 3.2 (32.3, 270) ns  5cm  5cm NIMA476 (02)  5cm

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 1H1H 2H2H 12 C 208 Pb CM system

Angular distribution in the LAB reference frame 1H1H 2H2H E n = 1MeV E n = 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 12 C(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 … … and a varying time distribution

p, , 12 C 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, …) (assumed same  and 12 C 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% (E th =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

EnEn 15cm  15cm MULT 1MULT 2MULT 3M2/M1 1 MeV BC %15.5%0.5%20.3% C6D669.3%12.5%0.24%18.1% 5 MeV BC %22.3%2.3%45.2% C6D645.3%18.6%2.4%41.1% E n = 1 MeVE n = 5 MeV E th =100keV

EnEn 5cm  15cm MULT 1MULT 2MULT 3M2/M1 1 MeV BC %5.1%0.1%8.28% C6D644.1%3.9%0.04%8.87% 5 MeV BC %3.6%0.2%11.35% C6D627.1%2.9%0.15%10.55% E n = 1 MeVE n = 5 MeV E th =100keV

EnEn 15cm  15cm BC501C6D6 1 MeV2.8%5.6% 5 MeV6.3%10.4% Ratio of counts scattered to outer detectors respect to central detector in the energy window [E max /2,E max ] EnEn 5cm  15cm BC501C6D6 1 MeV1.4%2.5% 5 MeV2.6%3.5% E n = 1 MeV E n = 5 MeV 15cm  15cm

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