Invariant-mass spectroscopy of neutron halo nuclei

Takashi Nakamura中村隆司

Tokyo Institute of Technology東京工業大学

中日 NP 06 , Shanghai

T.Nakamura, A.M. Vinodkumar,T.Sugimoto,N.Fukuda, M.Miura, Y.Kondo, N.Aoi, N.Imai,T.Kubo, T.Kobayashi, T.Gomi, A.Saito, H.Sakurai, S.Shimoura,D.Bazin, H.Hasegawa, H.Baba, T. Motobayashi, T.Yakushiji, Y. Yanagisawa,K.Yoneda, K. Watanabe, Y.X.Watanabe, M.Ishihara

Collaborators

Coulomb Breakup of 11LiSubmitted to Phys.Rev.Lett.

Invariant Mass Method (unbound excited states)

RadioactiveIon beam

BreakupKinematicFocusing

Well-defined Energy by Invariant Mass

ThickTarget

Ex

12Be vs. 14Be

12Be0+

2+0+

1-

2.24

2.70 MeV

2.10

14Be Drip line

11Be+n3.169 MeV

0+

1.264 MeV

? 2+

12Be+2nBound RegionInbeam spectroscopy

Unbound RegionInvariant massspectroscopy

14Be + 12C 12Be + n + n + 12C

Eex = S2n + Erel = 1.56 0.13 MeV

Erel (MeV)

d/d

Ere

l(mb/

MeV

)

T.Sugimoto, TN et al., (2006)

1.56MeV

N=8MagicityLoss

HHe

LiBeBC

NO

FNe

Neutron Dripline

N=8

N=20

11Be19C

N

Z Neutron halosStudied by InvariantMass Method by our group

11Li

11Li11Be

2n halo nucleus1n halo nucleus

Neutron Halo Nuclei– Nuclei at the stability limit

9Li

n

n10Ben

Sn=504 keV S2n=300 keV

14Be

11Li

High-Z Target (Pb)

9Li

n

= NE1(Ex)dB(E1)dEx

dCD

dEx 9hc163

Cross section = (Photon Number)xTransition Probability)

Invariant Mass

Equivalent Photon Method

relx , EE

)Li(),(),( 9PnPnP

11Li*

n

Coulomb Breakup of 11Li

11Be : E1 Response of one-neutron Halo

Ex10~20MeV

1~2MeV

N.Fukuda, TN et al., PRC70, 054606 (2004) TN et al.,PLB 331,296(1994)

core n

dB(E1)dEx

)W.u06.029.3(

fm06.005.1)1( 22

eEB

11Be

dB(E1)dEx

exp(iqr)| rY1m|gs

|2

ZA

-Sn

~ |exp(-r/)/r|2

Fourier Transform

Low-lying E1 Strength Halo State

exp(iqr)| rY1m|s1/2 |2Z

A

Direct Breakup Mechanism

Sn=504keV

= 0.72

One neutron halo nucleus vs. Two neutron halo nucleus

9Li

n

n10Ben

Motion between core and 1 valence neutron

Motion between 1. Core and neutron2. Core and neutron3. Two valence neutrons (neutron-neutron correlations)

S2n=300 keVSn=504 keV

Coulomb Dissocitaion of 11Li (Summary of Previous Results)

RIKEN @ 43MeV/nucleonPLB348 (1995) 29.

GSI @280MeV/nucleonNPA 619 (1997) 151.

MSU@ 28MeV/nucleonPRL 70 (1993) 730.PRC 48(1993) 118.

• RIPS@RIKEN• Primary Beam

18O 100 AMeV• Projectile Frag

mentation• Secondary Bea

m11Li ~70 AMeV~20 kcps

RIKENProjectile-fragment Separator

18O 100 AMeV

11Li ~70 AMeV

11Li

9Li

nn

Experimental Setup@RIPS at RIKEN

Pb Target

NEUT

HOD

BOMAG

DC

DALI

70MeV/nucleon

Examine Different Wall Events

t1

t2

1

2

12

Condition: 121 Almost no bias

Eth=6MeVee to avoid any gamma related events

Elimination of Cross-Talk events

Coulomb Dissociation Spectrum of 11Li

MeV3for

b.)(28.0.)(05.034.2

rel

E

syststat

Angular Distribution

Calculation:H.Esbensen et al.,NPA542(1992)310. Private Communication

“Soft dipole excitations in 11Li”

Present Result

Comparison with the 3-bodytheorykeV3002 nS

= NE1(Ex)dB(E1)dEx

dCD

dEx 9hc163

B(E1) Distribution

MeV3

18.042.1)1(

rel

22

E

fmeEB

Non-energy weightedE1 Cluster Sum Rule

22

2

212

22

1

2

0

3

)(24

3)1()1(

nc

xx

rA

Ze

rrrrA

ZedE

dE

EdBEB

r1

r2 n

9Li

rc-2n

fm32.001.5

)22(78.1

)3MeV(18.042.1)1(

2

2

22

rel22

ncr

fme

EfmeEB

(Extrapolated cluster strength)

~70% larger than non-correlatedstrength 021 rr

deg50~12

H.Esbensen et al.,NPA542(1992)310.

Experimental Result

E(9Li-n)

E(9

Li-n

)

1MeV

1MeV

Simulation (Phase-space decay)

E(9Li-n)

E(9

Li-n

)

1MeV

1MeV

Correlation?

Summary

11Li(2n halo)+Pb (Coulomb Breakup)

Low-lying B(E1) Strength Could be used to see the 　　　　　　　　　　　　　　　　　　　　 nn correlation & 9Li-n correlation in 11Li (E1 Non-energy weighted sum rule)

Strong B(E1) at very low excitation energy 2218.042.1)1( fmeEB

c.f. B(E1)=1.05(6) e2fm2 for 11Be

Invariant Mass Spectroscopy ----Powerful Spectroscopic tool