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 TanakaTokyo Institute of Technology

　 17Ne 18Ne 19Ne 20Ne 21Ne 22Ne 23Ne 24Ne 25Ne 26Ne 27Ne 28Ne 29Ne 30Ne 31Ne 32Ne 　 34Ne

　 　 　 17F 18F 19F 20F 21F 22F 23F 24F 25F 26F 27F 　 29F 　 31F

　 13O 14O 15O 16O 17O 18O 19O 20O 21O 22O 23O 24O 26O 28O

　 　 12N 13N 14N 15N 16N 17N 18N 19N 20N 21N 22N 23N

　 9C 10C 11C 12C 13C 14C 15C 16C 17C 18C 19C 20C 　 22C

　 8B 10B 11B 12B 13B 14B 15B 　 17B 　 19B

　 7Be 9Be 10Be 11Be 12Be 　 14Be

　 　 6Li 7Li 8Li 9Li 　 11Li

　 3He 4He 　 6He 　 8He

1H 2H 3H 　

Background

Breakup reactions of extreme neutron-rich nuclei at Intermediate energies

Invariant Mass Spectroscopy involving Detection of Fast Neutrons

Oxygen Anomaly

Neutron Halo(11Li, 14Be, 22C, etc.)

9Li

n

n

11Li

Stable

Proton-rich

Neutron-rich

neutron number

prot

on n

umbe

r

Invariant Mass Spectroscopy

22

rel )(

ii

ii PPEE

"Mass" measurement of 26O (Unbound) for study of the Oxygen Anomaly

24O+n+n

Erel(relative energy)26O

E

)(2O)()O( 24rel

26 nmmEm

24On

)O(24P

27F

C targetE/A ~250 MeV )(nP

)(nP

n

26O (unbound)

@ 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

np

5

Momentum of Neutron

n+C, n+H →charged particles(p, α, etc.)

n

(r0, t0)(r1, t1)

Photomultiplier Tube

target

Time of Flight (TOF), Position→ E, p

Plastic scintillator

~10 m

nbeam

tl

tr

t1 ∝ tl + tr

x1 ∝ tl - tr

y1,z1=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 AcceptanceNeutron Detector "NEBULA"

NEUT

VETO(distinguish charged particle)

wall1

wall2

n

x 120 modules

✔ Key Component of spectrometer SAMURAI@RIKEN

→ evaluation of NEBULA

p

SAMURAI Commissioning Experiment 1

n

p

natLi

・ Quasi-monoenergetic・ Single Neutron・ Cross Section is well known→ TOF Resolution, Efficiency

p

7Li(p,n)7Be(g.s.+0.43 MeV)

200 MeV(250 MeV)

NEBULA

SAMURAI MagnetBmax=3T, superconducting

Time of Flight ResolutionThreshold level = 6 MeVee θlab < ±40 mrad

Cou

nts

TOF(measured) - TOF(calculate) (ns)

σTOF=335(5) ps

7Li(p,n)7Be(g.s.+0.43MeV)

6Li(p,n)6Be (4.4%)

7Be other excited states + scattered neutrons

total

Intrinsic Resolution:σTOF=263(6) ps

All effects not related to NEBULA taken into account

cf.) ~300 ps (design value)

EfficiencyC

ount

s

En (MeV)

7Li(p,n)7Be(g.s.+0.43MeV)

6Li(p,n)6Be (4.4%)

7Be other excited states + scattered neutrons

total32.3(4) %

~6% correctionfor neutron flux loss, etc.

Intrinsic Efficiency:34.7±0.4(stat.)±1.0(syst.)%

Threshold level = 6 MeVee θlab < ±40 mrad

cf.) 37% Geant4 with INCLXX 40% DEMONS

SAMURAI Commissioning Experiment 2

・ 2-neutron event→ cross-talk rejection

C(14Be,12Be+n+n)

220 MeV/A

NEBULA

14Ben

n

12Be

C

SAMURAI MagnetBmax=3T, superconducting

2-neutron event and Cross-talk event

cross-talk event satisfyβ12 < β01

NEUTVETO

wall1

wall2

n

pn

n

np

β12

β01

β02

2-neutron event selection: β01/β12 < 1

→ β12 > β01

can only be 2-neutron event

2-neutron

Cross-talk event

1-neutron

1-Neutron EventPb(15C,14C+n)

β01/β12

Cou

nts

fake 2-neutron Crosstalk

2-Neutron EventC(14Be,12Be+n+n)

β01/β12

Cou

nts

2-neutron Crosstalk(+ 2-neutron)

13% 43%(~2% is fake)

(0 MeV < Erel <1 MeV)

→ ~1/20 contribution

C(14Be,12Be+n+n)

Erel (MeV)

β 01/

β 12

preliminary

Cou

nts

T. Sugimoto et al., Phys. Lett. B 654, 160 (2007)

projectionto x axis

14Be (2+)

is valid cross-talk rejection procedure !!

β01/β12 < 1

En=68 MeV/A

87(5) keV (1σ)

100 keV (1σ)

Development of Simulator

✔ 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)

✔ Simulation is Needed for Analysis and Development of Neutron Detector ・ response function ・ acceptance ・ efficiency etc.

Development of Simulator

(En=200 MeV)

Evaluation of Simulator

INCLXX

MENATER

Experiment

BERT

Light Output (MeVee)

Cou

nts

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)

Effi

cien

cy(s

im.)

/ E

ffici

ency

(exp

.)

w/o 12C(n,p)12BMENATER

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)

Effi

cien

cy (

%)

MENATER

BERT INCLXX

Experiment

Development of HIME

12cm

12cm

1.8m

4cm

2cm1m1.7m

40cm

40cm10cm

NEBULA y~5cm, x=z~3.5cm, t~0.2ns

Erel=84 keV (1σ) @1MeV

HIMEx=y~1.2cm, z~0.6cm, t~0.1ns

Erel=40 keV (1σ) @1MeV

HIgh resolution detector array for Multi-neutron EventsNeutron Detector "HIME"

NEBULA β01/β12 < 1 → lose about half of 2-neutron event

Cross-talk Rejection Method

NEBULA: ε4n~0.01%

Cross-talk Rejection Method

HIME tracking of recoiled proton

calculate the scattered neutron kinematics

Cross-talk Rejection Method

z1000 1010 1020 1030 1040

0-20

20

0

-20

-10

10

20

y

x

Geant4 Simulation

n

p

n

p

n

n

n

p

n

p

n

2-neutron1-neutron

Cross-talk eventn

p

n

signal position of one event

1000 1010 1020 1030 10400-20

20

0

-20

-10

10

20

y

x 1000 1010 1020 1030 10400-20

20

0

-20

-10

10

20

y

x

Cross-talk Rejection Method

z

assume n+p elastic

Geant4 Simulation

signal position of one event

Cross-talk Rejection Method

HIME: ε4n~1% (goal)

z1000 1010 1020 1030 1040

0-20

20

0

-20

-10

10

20

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 (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

― 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

backup

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

Time of Flight ResolutionEn = 200 MeVThreshold level = 6 MeVee θlab < ±40 mrad

Cou

nts

TOF(measured) - TOF(calculate) (ns)

σTOF=335(5) ps

7Li(p,n)7Be(g.s.+0.43MeV)

6Li(p,n)6Be (4.4%)

7Be other excited states + scattered neutrons

total

σTOF=263(6) ps (En = 200 MeV)σTOF=257(8) ps (En = 250 MeV)

subtract fluctuation of・ beam velocity・ time of neutron origin

NEBULA's contribution to TOF resolution:

Energy ResolutionEn = 200 MeVThreshold level = 6 MeVee θlab < ±40 mrad

Cou

nts

/ 0.

1 ns

Energy (MeV)

σE=2.59(4) MeV

7Li(p,n)7Be(g.s.+0.43MeV)

6Li(p,n)6Be (4.4%)

7Be other excited states + scattered neutrons

total

σE=2.03(5) MeV (En = 200 MeV)σE=3.00(8) MeV (En = 250 MeV)

subtract fluctuation of・ neutron velocity・ time of neutron origin

EfficiencyEn = 200 MeVThreshold level = 6 MeVee θlab < ±40 mrad

Cou

nts

En (MeV)

7Li(p,n)7Be(g.s.+0.43MeV)

6Li(p,n)6Be (4.4%)

7Be other excited states + scattered neutrons

total

34.7(4)% (En = 200 MeV)34.3(7)% (En = 250 MeV)

32.3(4) %

according to simulation~ 6-7% correction need

NEBULA's intrinsic efficiency:

26.0(7) mbar/sr @ 200 MeV → 2.7 %

EfficiencyEn = 200 MeVThreshold level = 6 MeVee θlab < ±40 mrad

Cou

nts

En (MeV)

7Li(p,n)7Be(g.s.+0.43MeV)

6Li(p,n)6Be (4.4%)

7Be other excited states + scattered neutrons

total

32.3(4) %

NEBULA's intrinsic efficiency:

count right part of energy dist. → 20508 countsfull fit procedure → 20191 counts

1.5% difference (FWHM)

TOF resolution correction

Efficiency correction

6.9% (En = 200 MeV)6.2% (En = 250 MeV)

~ 6-7% correction・ neutron flux loss by materials - Li target - neutron window - air between neutron window and NEBULA・ scattered neutrons

~3%

~3%

One-Neutron EventPb(15C,14C+n)

Two-Neutron EventC(14Be,12Be+n+n)

Erel (MeV)

β 01/

β 12

Erel (MeV)

β 01/

β 12

One-Neutron EventPb(15C,14C+n)

Two-Neutron EventC(14Be,12Be+n+n)

β01/β12 β01/β12

Cou

nts

Cou

nts

(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

Nuclear Instruments and Methods inPhysics Research A 491 (2002) 492–506

model limit ~200 MeV < Ein < ~10 GeV

(Journal of Physics: Conference Series 119 (2008) 032024)

DEMONS

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

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

6 MeVee

Threshold (MeVee)

Eff

icie

ncy(

sim

.) /

Eff

icie

ncy(

exp.

)

Detection Method

classical detection technic tracking 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: ε4n~1% (goal)NEBULA: ε4n~0.01%

n

pp

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 eventtracked event (n>=3)

8.8%

3.3% 37%18%

Efficiency and Erel Resolution

Relative Energy (MeV)R

elat

ive

Ene

rgy

Res

olut

ion

(keV

)

40 keV

42 keV

improve only ~5%

En (MeV)

Effi

cien

cy (

%)

ordinary event

tracked event (n>=3)

(En = 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

12B 10Li(1+,2+)9Li+n

Two p-wave states ( p3/2)x (p1/2) 1+, 2+)should be there! But not yet clarified . (Myo et al. TOSM)

10Li (1+ and 2+)

10Li (1+ and 2+)

1+ 2+

(RIBF exp. Planned @250MeV/nucleon)

Erel(9Li+n) Erel(9Li+n)

Experimental Setup-I

Measure

Timing Resolution, andAbsolute Detection Efficiency @Ein=250MeV

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)

Experimental Setup-II

Measure Relative Efficiency @Ein=100/ 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