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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.

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Presentation on theme: "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."— Presentation transcript:

1 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

2 17 Ne 18 Ne 19 Ne 20 Ne 21 Ne 22 Ne 23 Ne 24 Ne 25 Ne 26 Ne 27 Ne 28 Ne 29 Ne 30 Ne 31 Ne 32 Ne 34 Ne 17 F 18 F 19 F 20 F 21 F 22 F 23 F 24 F 25 F 26 F 27 F 29 F 31 F 13 O 14 O 15 O 16 O 17 O 18 O 19 O 20 O 21 O 22 O 23 O 24 O 26 O 28 O 12 N 13 N 14 N 15 N 16 N 17 N 18 N 19 N 20 N 21 N 22 N 23 N 9C9C 10 C 11 C 12 C 13 C 14 C 15 C 16 C 17 C 18 C 19 C 20 C 22 C 8B8B 10 B 11 B 12 B 13 B 14 B 15 B 17 B 19 B 7 Be 9 Be 10 Be 11 Be 12 Be 14 Be 6 Li 7 Li 8 Li 9 Li 11 Li 3 He 4 He 6 He 8 He 1H1H 2H2H 3H3H Background Breakup reactions of extreme neutron-rich nuclei at Intermediate energies  Invariant Mass Spectroscopy involving Detection of Fast Neutrons Oxygen Anomaly Neutron Halo ( 11 Li, 14 Be, 22 C, etc.) 9Li9Li n n 11 Li Stable Proton-rich Neutron-rich neutron number proton number

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

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 n p 5 Momentum of Neutron n+C, n+H → charged particles ( p, α, etc. ) n (r 0, t 0 ) (r 1, t 1 ) Photomultiplier Tube target Time of Flight (TOF), Position → E, p Plastic scintillator ~10 m n beam tltl trtr t 1 ∝ t l + t r x 1 ∝ t l - t r y 1,z 1 =geo. z x y

6 Development of NEBULA

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

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

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

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

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

12 2-neutron event and Cross-talk event cross-talk event satisfy β 12 < β 01 NEUT VETO wall1 wall2 n p n n n p β 12 β 01 β 02 2-neutron event selection: β 01 /β 12 < 1 → β 12 > β 01 can only be 2-neutron event 2-neutron Cross-talk event 1-neutron

13 1-Neutron Event Pb( 15 C, 14 C+n) β 01 /β 12 Counts fake 2-neutron Crosstalk 2-Neutron Event C( 14 Be, 12 Be+n+n) β 01 /β 12 Counts 2-neutron Crosstalk (+ 2-neutron) 13% 43% (~2% is fake) (0 MeV < E rel <1 MeV) → ~1/20 contribution

14 C( 14 Be, 12 Be+n+n) E rel (MeV) β 01 /β 12 preliminary Counts T. Sugimoto et al., Phys. Lett. B 654, 160 (2007) projection to x axis 14 Be (2 + ) is valid cross-talk rejection procedure !! β 01 /β 12 < 1 E n =68 MeV/A 87(5) keV (1σ) 100 keV (1σ)

15 Development of Simulator

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

17 Evaluation of Simulator INCLXX MENATER Experiment BERT Light Output (MeVee) Counts 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).

18 INCLXX gives best agreement Evaluation of Simulator BERT INCLXX MENATER Light Output Threshold (MeVee) Efficiency(sim.) / Efficiency(exp.) w/o 12 C(n,p) 12 B MENATER 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). Light Output Threshold (MeVee) Efficiency (%) MENATER BERT INCLXX Experiment

19 Development of HIME

20 12cm 1.8m 4cm 2cm 1m 1.7m 40cm 10cm NEBULA  y ~5cm,  x =  z ~3.5cm,  t ~0.2ns  E rel =84 keV HIME  x =  y ~1.2cm,  z ~0.6cm,  t ~0.1ns  E rel =40 keV HIgh resolution detector array for Multi-neutron Events Neutron Detector "HIME"

21 NEBULA β 01 /β 12 < 1 → lose about half of 2-neutron event Cross-talk Rejection Method NEBULA: ε 4n ~0.01%

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

23 Cross-talk Rejection Method z y x Geant4 Simulation n p n p n n n p n p n 2-neutron1-neutron Cross-talk event n p n signal position of one event

24 y x y x Cross-talk Rejection Method z assume n+p elastic Geant4 Simulation signal position of one event

25 Cross-talk Rejection Method HIME: ε 4n ~1% (goal) z y x Cross-talk event Geant4 Simulation signal position of one event n p n p n 1-neutron

26 conclusions ― large acceptance neutron detector NEBULA ― ・ TOF Resolution : 263(6) ps (E n =200 MeV) → achieved the design value ~300 ps ・ Efficiency : 34.7±0.4(stat.)±1.0(syst.)% (E n =200 MeV) → good agreement with newly developed simulator: 37% ・ Cross-talk rejection: β 01 /β 12 < 1 ~1/20 contribution of cross-talk for 14 Be measurement ― next generation neutron detector HIME ― ・ Relative Energy Resolution 40 keV at Erel=1 MeV ・ 2-neutron event selection method is established ― Simulation ― ・ New simulation code reproduce SAMURAI experiment

27 backup

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

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

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

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

32 26.0(7) 200 MeV → 2.7 %

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

34 TOF resolution correction

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

36 One-Neutron Event Pb( 15 C, 14 C+n) Two-Neutron Event C( 14 Be, 12 Be+n+n) E rel (MeV) β 01 /β 12 E rel (MeV) β 01 /β 12

37 One-Neutron Event Pb( 15 C, 14 C+n) Two-Neutron Event C( 14 Be, 12 Be+n+n) β 01 /β 12 Counts (0 MeV < E rel < 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, 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 Nuclear Instruments and Methods in Physics Research A 491 (2002) 492–506 model limit ~200 MeV < Ein < ~10 GeV (Journal of Physics: Conference Series 119 (2008) )

40 DEMONS

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

42

43

44

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

46 Detection Method classical detection technictracking detection NEBULA HIME ― reconstruct momentum by a signal from one module ― reconstruct momentum by a track of recoiled proton → efficient cross-talk rejection for multi-neutron detection HIME: ε 4n ~1% (goal) NEBULA: ε 4n ~0.01%

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

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

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

50 Simulated Example HIME NEBULA 12 B  10 Li(1 +,2 + )  9 Li+n Two p-wave states (  p 3/2 )x (p 1/2 )  1 +, 2 + ) should be there! But not yet clarified. (Myo et al. TOSM) 10 Li (1+ and 2+) 10 Li (1+ and 2+) (RIBF exp. E rel ( 9 Li+n)

51

52 Experimental Setup-I Measure Timing Resolution, and Absolute Detection in =250MeV 1. Event-by-event setup ・ Low event rate (~380 events/h, Beam 5x10 5 cps)– Use of T0 Detector ・ Accurate beam rate ・ Better T Resolution ( < 0.1ns)

53 Experimental Setup-II Measure Relative 250 MeV 2. High-Intensity Setup ・ High event rate (T0 detector– Removed) ・ Lower accuracy for beam rate ・ Long TOF (Better E spectrum)

54 test with cosmic ray is ongoing (will be presented by T. Nakashima) test exp. will be performed at RCNP


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