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

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

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

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

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

Development of NEBULA

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

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

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)

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

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

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

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

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)

Development of Simulator

✔ 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)

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).

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

Development of HIME

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"

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

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

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

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

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

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

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

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:

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

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:

26.0(7) 200 MeV → 2.7 %

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)

TOF resolution correction

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%

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

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)

・ 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, 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) )

DEMONS

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

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

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%

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

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

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)

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)

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)

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)

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