不安定核反応実験における 高速中性子の検出 Fast Neutron Detection in Unstable Nuclei Reaction Experiment

1. 不安定核反応実験における高速中性子の検出Fast Neutron Detection inUnstable Nuclei Reaction Experiment Ryuki Tanaka Tokyo Institute of Technology

2. Background Proton-rich n 9Li n Oxygen Anomaly proton number 11Li Neutron Halo (11Li, 14Be, 22C, etc.) Stable Neutron-rich neutron number Breakup reactions of extreme neutron-rich nuclei at Intermediate energies  Invariant Mass Spectroscopy involving Detection of Fast Neutrons

3. Invariant Mass Spectroscopy "Mass" measurement of 26O (Unbound) for study of the Oxygen Anomaly E 26O Erel(relative energy) 24O+n+n Neutron Measurement 26O (unbound) n 27F 24O n E/A ~250 MeV C target @ RIBF, RIKEN

4. 1. Development of the large acceptance neutron detector "NEBULA" 3. Development of next generation neutron detector "HIME" 2. Evaluation of newly developed simulator

5. Momentum of Neutron 5 Photomultiplier Tube y tl z Plastic scintillator x target (r1, t1) ~10 m (r0, t0) p n n n beam n+C, n+H → charged particles (p, α, etc.) Time of Flight (TOF), Position →E, p t1 ∝tl + tr x1 ∝tl - tr y1,z1=geo. tr

6. Development of NEBULA

7. Neutron Detector "NEBULA" NEutron-detection system for Breakup of Unstable-nuclei with Large Acceptance ✔ Key Component of spectrometer SAMURAI@RIKEN 24cm+24cm 180cm x 120 modules wall2 p n 360cm wall1 NEUT VETO (distinguish charged particle) a Single Module (NEUT) 180cm 12cm SAMURAI Commissioning Experiment in March 2012 12cm → evaluation of NEBULA

8. SAMURAI Commissioning Experiment 1 ・Quasi-monoenergetic ・Single Neutron ・Cross Section is well known → TOF Resolution, Efficiency 7Li(p,n)7Be(g.s.+0.43 MeV) SAMURAI Magnet Bmax=3T, superconducting p p n natLi 200 MeV (250 MeV) NEBULA

9. Time of Flight Resolution Threshold level = 6 MeVee θlab < ±40 mrad 7Li(p,n)7Be(g.s.+0.43MeV) σTOF=335(5) ps Counts total 7Be other excited states + scattered neutrons 6Li(p,n)6Be (4.4%) All effects not related to NEBULA taken into account TOF(measured) - TOF(calculate) (ns) Intrinsic Resolution: σTOF=263(6) ps cf.) ~300 ps (design value)

10. Efficiency Threshold level = 6 MeVee θlab < ±40 mrad 7Li(p,n)7Be(g.s.+0.43MeV) 32.3(4) % Counts total 6Li(p,n)6Be (4.4%) 7Be other excited states + scattered neutrons ~6% correction for neutron flux loss, etc. Intrinsic Efficiency: 34.7±0.4(stat.)±1.0(syst.)% En (MeV) cf.) 37% Geant4 with INCLXX 40% DEMONS

11. SAMURAI Commissioning Experiment 2 C(14Be,12Be+n+n) ・2-neutron event → cross-talk rejection SAMURAI Magnet Bmax=3T, superconducting n n 14Be C 220 MeV/A NEBULA 12Be

12. 2-neutron event and Cross-talk event wall2 β12 wall1 NEUT VETO p p n n n n Cross-talk event β02 cross-talk event satisfy β12 < β01 β01 → β12 > β01 can only be 2-neutron event 2-neutron event selection: β01/β12 < 1 2-neutron 1-neutron

13. 1-Neutron Event Pb(15C,14C+n) 2-Neutron Event C(14Be,12Be+n+n) fake 2-neutron Crosstalk 2-neutron Crosstalk (+ 2-neutron) Counts Counts 43% (~2% is fake) 13% → ~1/20 contribution β01/β12 β01/β12 (0 MeV < Erel <1 MeV)

14. C(14Be,12Be+n+n) 87(5) keV (1σ) preliminary Counts β01/β12 projection to x axis Erel (MeV) T. Sugimoto et al., Phys. Lett. B 654, 160 (2007) En=68 MeV/A 100 keV (1σ) 14Be (2+) β01/β12 < 1 is valid cross-talk rejection procedure !!

15. Development of Simulator

16. Development of Simulator ✔Simulation is Needed for Analysis and Development of Neutron Detector ・ response function ・ acceptance ・ efficiency etc. ✔ Simulator for neutron detector array is Not established for En ~ 250 MeV neutron → ・ developed new simulator with Geant4 ・ compare with SAMURAI commissioning data 7Li(p,n)7Be(g.s.+0.43 MeV) (En=200 MeV)

17. Evaluation of Simulator compare three physics models for n+plastic scintilator ・ BERT (intranuclear cascade model) ・ INCLXX (intranuclear cascade model) ・ MENATE_R (treat each reaction channel) Z. Kohley et al., Nucl. Instr. and Meths. A 682, 59 (2012). BERT Experiment Counts MENATER INCLXX Light Output (MeVee)

18. Evaluation of Simulator compare three physics models for n+plastic scintilator ・ BERT (intranuclear cascade model) ・ INCLXX (intranuclear cascade model) ・ MENATE_R (treat each reaction channel) Z. Kohley et al., Nucl. Instr. and Meths. A 682, 59 (2012). w/o 12C(n,p)12B MENATER MENATER MENATER Efficiency (%) Efficiency(sim.) / Efficiency(exp.) Experiment BERT INCLXX BERT INCLXX Light Output Threshold (MeVee) Light Output Threshold (MeVee) INCLXX gives best agreement

19. Development of HIME

20. Neutron Detector "HIME" HIgh resolution detector array for Multi-neutron Events 1.8m 12cm 12cm NEBULA sy~5cm, sx=sz~3.5cm, st~0.2ns DErel=84 keV (1σ) @1MeV 10cm 40cm 1.7m 40cm 1m 2cm HIME sx=sy~1.2cm, sz~0.6cm, st~0.1ns DErel=40 keV (1σ) @1MeV 4cm

21. Cross-talk Rejection Method NEBULA β01/β12 < 1 → lose about half of 2-neutron event NEBULA: ε4n~0.01%

22. Cross-talk Rejection Method HIME tracking of recoiled proton calculate the scattered neutron kinematics

23. Cross-talk Rejection Method Geant4 Simulation z 1010 1000 1020 1030 1040 x -20 0 20 20 Cross-talk event 10 p p p p p n n n n n n n n n y 0 2-neutron 1-neutron -10 -20 signal position of one event

24. Cross-talk Rejection Method Geant4 Simulation z 1010 1010 1000 1000 1020 1020 1030 1030 1040 1040 x x -20 -20 0 0 20 20 20 20 assume n+p elastic 10 10 y y 0 0 -10 -10 -20 -20 signal position of one event

25. Cross-talk Rejection Method Geant4 Simulation z 1010 1000 1020 1030 1040 x -20 0 20 20 Cross-talk event 10 p p n n n y 0 1-neutron -10 -20 signal position of one event HIME: ε4n~1% (goal)

26. conclusions ― large acceptance neutron detector NEBULA ― ・ TOF Resolution : 263(6) ps (En=200 MeV) → achieved the design value ~300 ps ・ Efficiency : 34.7±0.4(stat.)±1.0(syst.)% (En=200 MeV) → good agreement with newly developed simulator: 37% ・ Cross-talk rejection: β01/β12 < 1 ~1/20 contribution of cross-talk for 14Be measurement ― Simulation ― ・ New simulation code reproduce SAMURAI experiment ― next generation neutron detector HIME ― ・ Relative Energy Resolution 40 keV at Erel=1 MeV ・ 2-neutron event selection method is established

27. backup

28. Analysis of NEBULA 7Li(p,n)7Be(g.s.+0.43 MeV)

29. Time of Flight Resolution En = 200 MeV Threshold level = 6 MeVee θlab < ±40 mrad 7Li(p,n)7Be(g.s.+0.43MeV) σTOF=335(5) ps Counts total 7Be other excited states + scattered neutrons 6Li(p,n)6Be (4.4%) subtract fluctuation of ・ beam velocity ・ time of neutron origin TOF(measured) - TOF(calculate) (ns) σTOF=263(6) ps (En = 200 MeV) σTOF=257(8) ps (En = 250 MeV) NEBULA's contribution to TOF resolution:

30. Energy Resolution En = 200 MeV Threshold level = 6 MeVee θlab < ±40 mrad 7Li(p,n)7Be(g.s.+0.43MeV) σE=2.59(4) MeV Counts / 0.1 ns total 7Be other excited states + scattered neutrons 6Li(p,n)6Be (4.4%) subtract fluctuation of ・ neutron velocity ・ time of neutron origin Energy (MeV) σE=2.03(5) MeV (En = 200 MeV) σE=3.00(8) MeV (En = 250 MeV)

31. Efficiency En = 200 MeV Threshold level = 6 MeVee θlab < ±40 mrad 7Li(p,n)7Be(g.s.+0.43MeV) 32.3(4) % Counts total 7Be other excited states + scattered neutrons 6Li(p,n)6Be (4.4%) according to simulation ~ 6-7% correction need En (MeV) 34.7(4)% (En = 200 MeV) 34.3(7)% (En = 250 MeV) NEBULA's intrinsic efficiency:

32. 26.0(7) mbar/sr @ 200 MeV → 2.7 %

33. Efficiency En = 200 MeV Threshold level = 6 MeVee θlab < ±40 mrad 7Li(p,n)7Be(g.s.+0.43MeV) 32.3(4) % Counts total 7Be other excited states + scattered neutrons 6Li(p,n)6Be (4.4%) count right part of energy dist. → 20508 counts full fit procedure → 20191 counts En (MeV) 1.5% difference (FWHM) NEBULA's intrinsic efficiency:

34. TOF resolution correction

35. Efficiency correction ~ 6-7% correction ・ neutron flux loss by materials - Li target - neutron window - air between neutron window and NEBULA ・ scattered neutrons ~3% ~3% 6.9% (En = 200 MeV) 6.2% (En = 250 MeV)

36. One-Neutron Event Pb(15C,14C+n) Two-Neutron Event C(14Be,12Be+n+n) β01/β12 β01/β12 Erel (MeV) Erel (MeV)

37. One-Neutron Event Pb(15C,14C+n) Two-Neutron Event C(14Be,12Be+n+n) Counts Counts β01/β12 β01/β12 (0 MeV < Erel < 100 MeV)

38. ・ MENATE_R (treat each reaction channel) MENATE_R is ported code of neutron detector simulator MENATE written in FORTRAN

39. BERT, INCLXX (Geant4 built in class) ・ BERT: Bertini Intranuclear Cascade Model (Bertini: H. W. Bertini) - M. P. Guthrie, R. G. Alsmiller and H. W. Bertini, Nucl. Instr. Meth, 66, 1968, 29. - widely used ・ INCLXX: INCL++ → c++ version of INCL INCL: Liege Intranuclear Cascade Model (Liege: the Belgian city) - developed and validated against recent data - typical users are from the nuclear physics community studying spallation processes (Journal of Physics: Conference Series 119 (2008) 032024) Nuclear Instruments and Methods in Physics Research A 491 (2002) 492–506 model limit ~200 MeV < Ein < ~10 GeV

40. DEMONS

41. A. Del Guerra, Nucl. Instr. and Meths. 135, 337 (1976).

42. A. Del Guerra, Nucl. Instr. and Meths. 135, 337 (1976).

45. Efficiency(sim.) / Efficiency(exp.) 6 MeVee Threshold (MeVee)

46. Detection Method NEBULA HIME classical detection technic tracking detection ― reconstruct momentum by a signal from one module ― reconstruct momentum by a track of recoiled proton → efficient cross-talk rejection for multi-neutron detection NEBULA: ε4n~0.01% HIME: ε4n~1% (goal)

47. Cross-talk Rejection Geant4 Simulation 2n event Cross-talk event p p n p n p n n n n further simulation is ongoing

48. Time Resolution ordinary event tracked event (n>=3) Energy dependence of timing resolution

49. Efficiency and Erel Resolution ordinary event ordinary event Geant4 Simulation tracked event (n>=3) tracked event (n>=3) 8.8% 42 keV 18% 37% 3.3% 40 keV Relative Energy Resolution (keV) Efficiency (%) improve only ~5% En (MeV) Relative Energy (MeV) ・ optimization of timing calculation ・ HIME is to small ・ time resolution is already high (100 ps) (En = 250 MeV, 10 m, A=100) High Resolution is already obtained

50. Simulated Example 12B 10Li(1+,2+)9Li+n (RIBF exp. Planned @250MeV/nucleon) Two p-wave states ( p (p3/2)x n(p1/2)  1+, 2+) should be there! But not yet clarified . (Myo et al. TOSM) HIME NEBULA 10Li (1+ and 2+) 10Li (1+ and 2+) 2+ 1+ Erel(9Li+n) Erel(9Li+n)