H.SakuraiUniv. of Tokyo

Spectroscopy on light exotic nuclei

RIKEN Facility

RIKEN Ring Cyclotron

Experiment

RIPS (Riken Projectile Fragment Separator)

production target

In-flight RI beam production

Primary beam E/A~64-135 MeVRI beam E/A~30-90 MeV

K=540

RIPS (RIKEN Projectile-fragment Separator)

Primary beam

RI beam

RI productiontarge t

W edgeEnergy -deg rade r

S lit

S lit

required for secondary nuclear reactionslarge momentum acceptance,

solid angle and high magnetic rigidity

Second-generation PF separatorIntense RI beams

T.Kubo et al. NIMB70, 309(92)

Challenge in methodologyInvariant mass spectroscopy

for particle unbound statesIntermediate energy Coulomb excitation

for B(E2)　etc...

optimized for PF reaction

Progress of Research Opportunities with RI Beams Construction of a dedicated facility for RI beam productionvia the projectile fragmentation

SRC K=2500 350~400 A MeV 350A MeV U

present facilityRI beams A < 50 E ~ 50A MeV

RIBF

RIBF

RIPS

RIBFRI beams A < 200 E ~ 250A MeV

RIBFRI Beam Factory : the 3rd generation facility

in 2007

- “Magicity Loss” and Collective Motion -

Investigation on Nuclear Structure via In-beam Spectroscopy

Experimental setup for in-beam gamma spectroscopywith fast RI beams

RI beam

gamma-ray detector array　

Charged particle detectors

target

particle identification for ejectiles

NaI detector

Doppler-shift corrected spectrum

~50 A MeV

observation of de-excited rays

-ray energy and emission angle for Doppler correction

γ

beam

θE

2+

0+

γ

inverse reactionhigh energy beam ->

thick targetkinematical focusing ->

high efficiency

- “Magicity Loss” and Collective Motion -

Present Facility RIPS

1. Magicity loss at N~20 2. 16C

The New Facility RIBF

3. Future

Investigation on Nuclear Structure via In-beam Spectroscopy

Investigation for the island-of-inversion region

20

8

28

34Mg

30Ne

32MgSearch for new isotopes Particle stability 31Ne, 31F …In-beam gamma spectroscopy B(E2) <- CEX 32Mg, 34Mg E(2+), E(4+) <- Two step fragmentation 34Mg

How is the region extended ? lower Z and larger N

27F

31F

proton inelastic scattering 30Ne E(2+) 27F bound excited states

34Mg has a larger collectivity than 32Mg.

Why 31F is particle bound ?How large collectivity at Z=9, 10?

In-beam gamma spectroscopy

The first excited state of 30Ne via (p,p’)Yanagisawa et al., Phys. Lett. B 566 (2003) 84

0h

2h

30Ne32Mg34Si36S

N=20 Isotone

E(2

1+)

[keV

]

data

885 791

Luminosity Enhancement via Liquid Hydrogen target

30Ne Intensity ~ 0.2 /sec

Number of target nuclei

p Pb200 : 1

Cou

nts/

40ke

V

Energy [keV]

29Ne

28Ne

~200 mg/cm2

E(2+, 30Ne) < E(2+, 32Mg) 30Ne has a larger collectivity than 32Mg?

Elekes et al., PLB 599 (2004) 17

Bound excited states in 27F

Sn=1.4 MeV

27F

1.1

2.0

5/2+

1/2+

sdpf sdOtsuka et al. Brown

Two bound excited states for 25,26,27F via p(27F, 25,26,27F )

proton contribution across Z=8 gap??

One bound excited state predicted via sdpf-shell model <- neutron excitation across N=20

- “Magicity Loss” and Collective Motion -

Present Facility RIPS

1. Magicity loss at N~20 2. 16C

The New Facility RIBF

3. Future

Investigation on Nuclear Structure via In-beam Spectroscopy

unstable nucleilifetime

Coul. Ex.

Z<8

10Be 12Be 14Be

12C 14C 16C 18C 20C 22C

16O 18O 20O 22O 24O

20Ne 22Ne 24Ne 26Ne 28Ne 30Ne 32Ne 34Ne

24Mg 26Mg28Mg30Mg32Mg 34Mg36Mg38Mg

28Si 30Si 32Si 34Si 36Si 38Si 40Si

B(E2) measurement for the light mass region

stable nuclei

No data for the neutron-rich Be and C isotopes

B(E2)

CEX

Z<8 Coulomb Ex. < Nuclear Ex.

Density distribution of the C isotopes by AMD

proton neutron proton neutron

Y. Kanada-En’yo and H. Horiuchi, Prog. Theor. Phys. 142,205(2001)

unstable nucleilifetime

Coul. Ex.

Z<8

10Be 12Be 14Be

12C 14C 16C 18C 20C 22C

16O 18O 20O 22O 24O

20Ne 22Ne 24Ne 26Ne 28Ne 30Ne 32Ne 34Ne

24Mg 26Mg28Mg30Mg32Mg 34Mg36Mg38Mg

28Si 30Si 32Si 34Si 36Si 38Si 40Si

B(E2) measurement for 16C via a new techniques

stable nucleiB(E2)

Lifetime measurement of 2+ state

New method appropriate for fast RI beamshould be developed

“Recoil-Shadow-Method”

Z<8 Coulomb Ex. < Nuclear Ex. ~

2+

0+

CEX

• Inelastic Scattering of RI beams• High velocity () = c ~ 1.0 cm (=100ps, =0.3)• Thick lead shield “shadowing” for -rays in delayed emission = exp (- l ) : attenuation coeff. l : path length in lead

target (9Be)

Recoil-shadow-methodR1, R2 gamma detectors

R1/R2 ratio has mean life dependence

B(E2) /B(E2)sys=0.03

Anomalously hindered B(E2) of 16C

B(E2: 2+ -> 0+)

B(E2)sys=6.47Z2A-0.69E(2+)-1

Quantum liquid drop model

0.63 [e2fm4]

0.26 [W.u.]

S. Raman et.al.,PRC37, 805 (‘88).

= 77 +/- 14 (stat.) +/- 19 (syst.) [ps]

N. Imai et al, Phys.Rev.Lett. 92,062501(‘04)

em = 0.14

Neutron contribution to the 2+ state??

Proton Inelastic Scattering on 16CH.J. Ong et al, to be submitted to PRL

proton: the most sensitive probe for neutron matter

In-beam technique to obtain angular integrated cross section

= 24 +/- 4 mbDWBA analysis (ECIS)pp’ = 0.50 +/- 0.07 > em =0.14 pp’ = 1.42 +/- 0.21 fmErrors include optical potential dependences (CH89, p+12C, p+16O), too

10 20 50 100 200

mass number A

pp’ /

sys

pp’/sys ~1

16Csys = 466A-1E(2+)-1/2

Raman’s systematicsMagnitude of pp’ for 16C is the same as those of other nuclei.

Neutron-dominant collective motion

n/em =| Mn/Mp |/ (N/Z) = 4.0 +/- 1.4

10 20 50 100 200mass number A

1.Combination of em and pp’, based on Bernstein’s prescription

Disentanglement of proton and neutron contributions

Mn/

Mp /

(N

/Z)

H.J. Ong et al, to be submitted to PRL

em B(E2)=0.28(6) [W.u.]

2. Interference of nuclear and Coulomb excitation in inelastic scattering on Pb

Elekes et al., Phys.Lett.B 586, 34 (2004)

n/em=4.6 +/- 1

Imai et al. B(E2)=0.26 [W.u.]

New type of collective motion?

TWO quantum liquid drops

“exotic” picture for 16C case

proton matter neutron matter

Large contribution by neutron matter,not by proton matter

n/em=4 ~ 5

ONE quantum liquid drop

proton- and neutron matter’s contributions to collective motion are same.

“classical” picture

one-body nuclear matter

Why B(E2) is so small??

Z=6 magic number ?

Effective charges ?

Shell gaps from mass information proton-shell ~ 12 MeV a large gap between p3/2 and p1/2 neutron-shell < 1 MeV

en/e ~ 0 due to weak binding of neutrons?

Q-moments of 15,17B Izumi et al., PLB366 (1996)51 Ogawa et al., PRC67(2003)064308

Based on Audi et al., NPA 729(2003)337

Proton and neutron shell gaps from mass information

neutron number

neutron number

prot

on n

umbe

rpr

oton

num

ber

proton shell gap S2p(Z,N)-S2p(Z+2,N)

neutron shell gap S2n(Z,N)-S2n(Z,N+2)

16C

16C

MeV

MeV

Z=6

Z=6

N=10

N=10

H.Sakurai ENAM04

p1/2

p3/2

p1/2 s1/2d5/2

- “Magicity Loss” and Collective Motion -

Present Facility RIPS

1. Magicity loss at N~20 2. 16C

The New Facility RIBF

3. Future

Investigation on Nuclear Structure via In-beam Spectroscopy

Exploration towards heavier and more proton-rich /neutron-rich region

to produce a lot of data for “unified pictures”

RIBF

RIPS

50

50

82

82

126

2820

20

B(E2)-1 [1/W.u]

neutron number

prot

on n

umbe

r

132Sn

208Pb

78Ni double magicity?

N=34 new magicity?N=28 magicity?

N=82 magicity?

deformation region?48Ni double magicity?

100Sn double magicity?

Subjects of nuclear structure and collectivity

2001

CEX -> B(E2)(p,p’) -> 2

neutron skins ? collectivity originated from neutrons in skinpairing ? rotation energy v.s. pairing energyexotic modes ? originated from two asymmetric liquids...

Higher excited states and higher spin statesfor exotic phenomena of collectivity?

not only low lying states but also ...

J, Ex

for intermediate and heavy mass system

Summary

Anomalous quadrupole collectivity of 16C

proton matter neutron matter

neutron-dominant collectivityHow about 18C, 20C … ?

B(E2), (p,p’), Interference

n/em= 4~5 > 1

Island of inversion30Ne E(2+, 30Ne) < E(2+, 32Mg) 30Ne has a larger collectivity than 32Mg?27F two bound excited states. proton contributions across Z=8?

For future

Any exotic collective motion proposed in medium- and heavy-mass region?