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 Ryuki Tanaka Tokyo Institute of Technology Background 17 Ne 18Ne 19Ne 20Ne 21Ne 22Ne 23Ne 24Ne 25Ne 26Ne 27Ne 28Ne 29Ne 30Ne 31Ne 32Ne 34 Ne Proton-rich proton number C C 8 3 1 H 6 Li He 4He 2 H 3 H F 20 F 21 Li 6 He 22 O O O O F 23 F 24 F 25 O O O O F 18 19 20 21 22 23 24 12 13 14 15 16 17 18 19 20 21 22 23 11 12 C 13 14 15 16 17 18 19 20 11 B 12 13 14 15 C N O N C B N C B N C Be 10Be 11Be 12Be 7 F 17 O 9 Be Stable 19 16 B 7 F 15 10 B 18 14 N 10 F 13 O 9 17 8 Li 9 Li B N C N B C N C 17 B N C N C 19 B N O 26 F 27 26 F 29 O 28 31 F F O N Oxygen Anomaly 22 C 11Li 14 Be 11 Li Neutron Halo (11Li, 14Be, 22C, etc.) n 9Li 8 He Neutron-rich n neutron number Breakup reactions of extreme neutron-rich nuclei at Intermediate energies Invariant Mass Spectroscopy involving Detection of Fast Neutrons Invariant Mass Spectroscopy "Mass" measurement of 26O (Unbound) for study of the Oxygen Anomaly E 26O Erel(relative energy) 24O+n+n 27F E/A ~250 MeV @ RIBF, RIKEN 26O m(26 O) Erel m(24 O) 2m(n) (unbound) Neutron Measurement P(n ) n 24 P( O) P(n ) 24O n C target 2 2 Erel E ( Pi ) Pi i i 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 Photomultiplier Tube y tl z Plastic scintillator x target (r0, t0) beam ~10 m (r1, t1) n Time of Flight (TOF), Position → E, p n n p n+C, n+H → charged particles (p, α, etc.) tr t 1 ∝ t l + tr x1 ∝ tl - tr y1,z1=geo. Development of NEBULA Neutron Detector "NEBULA" NEutron-detection system for Breakup of Unstable-nuclei with Large Acceptance ✔ Key Component of spectrometer SAMURAI@RIKEN 24cm+24cm 180cm 12cm 12cm a Single Module (NEUT) x 120 modules 180cm wall2 wall1 NEUT 360cm VETO (distinguish charged particle) n p SAMURAI Commissioning Experiment in March 2012 → evaluation of NEBULA SAMURAI Commissioning Experiment 1 7Li(p,n)7Be(g.s.+0.43 MeV) ・Quasi-monoenergetic ・Single Neutron ・Cross Section is well known → TOF Resolution, Efficiency SAMURAI Magnet Bmax=3T, superconducting p 200 MeV (250 MeV) n natLi p NEBULA Time of Flight Resolution Threshold level = 6 MeVee θlab < ±40 mrad Counts 7Li(p,n)7Be(g.s.+0.43MeV) σTOF=335(5) ps total 6Li(p,n)6Be (4.4%) 7Be other excited states + scattered neutrons 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) Efficiency Threshold level = 6 MeVee θlab < ±40 mrad Counts 7Li(p,n)7Be(g.s.+0.43MeV) 32.3(4) % total 6Li(p,n)6Be (4.4%) 7Be other excited states + scattered neutrons ~6% correction for neutron flux loss, etc. En (MeV) Intrinsic Efficiency: 34.7±0.4(stat.)±1.0(syst.)% cf.) 37% Geant4 with INCLXX 40% DEMONS SAMURAI Commissioning Experiment 2 C(14Be,12Be+n+n) ・2-neutron event → cross-talk rejection SAMURAI Magnet Bmax=3T, superconducting 14Be n n C 220 MeV/A NEBULA 12Be 2-neutron event and Cross-talk event wall2 p n β12 wall1 p n NEUT VETO Cross-talk event β02 β01 cross-talk event satisfy β12 < β01 → β12 > β01 can only be 2-neutron event n n 2-neutron 1-neutron 2-neutron event selection: β01/β12 < 1 1-Neutron Event 2-Neutron Event Pb(15C,14C+n) C(14Be,12Be+n+n) Crosstalk 2-neutron Crosstalk (+ 2-neutron) Counts Counts fake 2-neutron 13% 43% (~2% is fake) → ~1/20 contribution β01/β12 β01/β12 (0 MeV < Erel <1 MeV) C(14Be,12Be+n+n) β01/β12 Counts 87(5) keV (1σ) projection to x axis Erel (MeV) T. Sugimoto et al., Phys. Lett. B 654, 160 (2007) En=68 MeV/A 100 keV (1σ) 14Be β01/β12 < 1 is valid cross-talk rejection procedure !! (2+) Development of Simulator 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) 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). Counts BERT Experiment MENATER INCLXX Light Output (MeVee) 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). MENATER w/o Experiment BERT INCLXX Light Output Threshold (MeVee) Efficiency(sim.) / Efficiency(exp.) Efficiency (%) MENATER 12C(n,p)12B MENATER BERT INCLXX Light Output Threshold (MeVee) INCLXX gives best agreement Development of HIME 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 40cm 10cm 1.7m 1m 40cm 2cm HIME sx=sy~1.2cm, sz~0.6cm, st~0.1ns DErel=40 keV (1σ) @1MeV 4cm Cross-talk Rejection Method NEBULA β01/β12 < 1 → lose about half of 2-neutron event NEBULA: ε4n~0.01% Cross-talk Rejection Method HIME tracking of recoiled proton calculate the scattered neutron kinematics Cross-talk Rejection Method Geant4 Simulation z x 20 1000 -20 0 1010 1020 1030 p 20 n n 2-neutron 1-neutron 10 y 0 n Cross-talk event n p -10 -20 signal position of one event 1040 Cross-talk Rejection Method Geant4 Simulation z x 20 1000 -20 0 1010 1020 1030 1040 20 assume n+p elastic 10 y 0 -10 -20 signal position of one event Cross-talk Rejection Method Geant4 Simulation z x 20 1000 -20 0 1010 1020 1030 1040 p 20 10 n y 1-neutron 0 n Cross-talk event n p -10 -20 signal position of one event HIME: ε4n~1% (goal) 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 backup Analysis of NEBULA 7Li(p,n)7Be(g.s.+0.43 MeV) Time of Flight Resolution En = 200 MeV Threshold level = 6 MeVee θlab < ±40 mrad Counts 7Li(p,n)7Be(g.s.+0.43MeV) σTOF=335(5) ps total 7Be 6Li(p,n)6Be other excited states + scattered neutrons (4.4%) subtract fluctuation of ・ beam velocity ・ time of neutron origin TOF(measured) - TOF(calculate) (ns) NEBULA's contribution to TOF resolution: σTOF=263(6) ps (En = 200 MeV) σTOF=257(8) ps (En = 250 MeV) Energy Resolution En = 200 MeV Threshold level = 6 MeVee θlab < ±40 mrad Counts / 0.1 ns 7Li(p,n)7Be(g.s.+0.43MeV) σE=2.59(4) MeV total 6Li(p,n)6Be 7Be (4.4%) Energy (MeV) other excited states + scattered neutrons subtract fluctuation of ・ neutron velocity ・ time of neutron origin σE=2.03(5) MeV (En = 200 MeV) σE=3.00(8) MeV (En = 250 MeV) Efficiency En = 200 MeV Threshold level = 6 MeVee θlab < ±40 mrad Counts 7Li(p,n)7Be(g.s.+0.43MeV) 32.3(4) % total 6Li(p,n)6Be 7Be (4.4%) other excited states + scattered neutrons En (MeV) NEBULA's intrinsic efficiency: according to simulation ~ 6-7% correction need 34.7(4)% (En = 200 MeV) 34.3(7)% (En = 250 MeV) 26.0(7) mbar/sr @ 200 MeV → 2.7 % Efficiency En = 200 MeV Threshold level = 6 MeVee θlab < ±40 mrad Counts 7Li(p,n)7Be(g.s.+0.43MeV) 32.3(4) % total 6Li(p,n)6Be 7Be (4.4%) other excited states + scattered neutrons En (MeV) NEBULA's intrinsic efficiency: count right part of energy dist. → 20508 counts full fit procedure → 20191 counts 1.5% difference (FWHM) TOF resolution correction Efficiency correction ~ 6-7% correction ・ neutron flux loss by materials - Li target - neutron window ~3% - air between neutron window and NEBULA ・ scattered neutrons ~3% 6.9% (En = 200 MeV) 6.2% (En = 250 MeV) Two-Neutron Event Pb(15C,14C+n) C(14Be,12Be+n+n) β01/β12 β01/β12 One-Neutron Event Erel (MeV) Erel (MeV) Two-Neutron Event Pb(15C,14C+n) C(14Be,12Be+n+n) Counts Counts One-Neutron Event β01/β12 β01/β12 (0 MeV < Erel < 100 MeV) ・ MENATE_R (treat each reaction channel) MENATE_R is ported code of neutron detector simulator MENATE written in FORTRAN 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 DEMONS A. Del Guerra, Nucl. Instr. and Meths. 135, 337 (1976). A. Del Guerra, Nucl. Instr. and Meths. 135, 337 (1976). Efficiency(sim.) / Efficiency(exp.) 6 MeVee Threshold (MeVee) Detection Method NEBULA classical detection technic ― reconstruct momentum by a signal from one module HIME tracking detection ― reconstruct momentum by a track of recoiled proton → efficient cross-talk rejection for multi-neutron detection NEBULA: ε4n~0.01% HIME: ε4n~1% (goal) Cross-talk Rejection Geant4 Simulation Cross-talk event 2n event p n p p n p n n nn further simulation is ongoing Time Resolution ordinary event tracked event (n>=3) Energy dependence of timing resolution Efficiency and Erel Resolution ordinary event Geant4 Simulation 8.8% 18% 3.3% 37% Relative Energy Resolution (keV) Efficiency (%) ordinary event tracked event (n>=3) tracked event (n>=3) 42 keV 40 keV 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 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 10Li (1+ and 2+) (1+ and 2+) 1+ 2+ Erel(9Li+n) Erel(9Li+n) Experimental Setup-I 1. Event-by-event setup ・Low event rate(~380 events/h, Beam 5x105 cps)– Use of T0 Detector ・Accurate beam rate ・Better T Resolution ( <0.1ns) Measure Timing Resolution, and Absolute Detection Efficiency @Ein=250MeV Experimental Setup-II 2. High-Intensity Setup ・High event rate (T0 detector– Removed) ・Lower accuracy for beam rate ・Long TOF (Better E spectrum) Measure Relative Efficiency @Ein=100/ 250 MeV test with cosmic ray is ongoing (will be presented by T. Nakashima) test exp. will be performed at RCNP
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