Invariant-mass spectroscopy of neutron-rich Be isotopes - PowerPoint Presentation

Slide1

Invariant-mass spectroscopy of neutron-rich Be isotopes

ContentsBreakup reactions of 14Be on a proton targetInelastic scattering (14Be)One-neutron removal reaction (13Be)

Y. Kondo

RIKEN

Nishina

CenterSlide2

2

CollaboratorsY. Kondo, T. Nakamura, Y. Satou, T. Matsumoto, N. Aoi, N. Endo, N. Fukuda, T. Gomi, Y. Hashimoto, M. Ishihara, S. Kawai, M. Kitayama, T. Kobayashi, Y. Matsuda, N. Matsui,T. Motobayashi, T. Nakabayashi, K. Ogata, T. Okumura, H. J. Ong, T. K. Onishi, H. Otsu, H. Sakurai, S. Shimoura, M. Shinohara, T. Sugimoto, S. Takeuchi, M. Tamaki, Y. Togano, Y. YanagisawaTokyo Institute of TechnologyRIKEN Nishina CenterTohoku UniversityRikkyo UniversityKyushu UniversityUniversity of TokyoCenter for Nuclear Study (CNS), University of TokyoSlide3

Nuclear Chart

Exotic structuresNeutron haloMagicity loss (12Be, 32Mg)Di-neutron correlation?　(6He, 11Li)Different deformation of proton/neutron density(16C)

Neutron halo

Magicity

loss

Different deformations of

Protons and neutrons

Di-neutron?

13

Be,

14

Be

3Slide4

14

BeDrip-line nucleusTwo neutron haloBorromean (12Be+n, n+n systems are unbound)No bound excited statesexcited states locate above the neutron separation energy (S2n=1.26MeV)13BeUnbound nucleusLow-lying levels are not clarifiedSeveral experimental results are not consistentBreakup of 14Be on proton14

Be and

13

Be

4Slide5

Inelastic

scatteringOne-neutron removal reaction14BeAngular distribution  Jp assignmentcross section collectivity

13

Be

Momentum distribution of

13

Be system



J

p

assignment

Breakup Reactions on a low-Z target

p

12

Be

n

n

14

Be

12

Be

n

n

q

12

Be

n

n

14

Be*

~ 70

MeV

/u

p

12

Be

n

n

14

Be

12

Be

n

q

12

Be

n

13

Be

n

~ 70 MeV/u

Coulomb breakup cross section is small

Invariant mass

5Slide6

Momentum Distribution of 13Be (transverse)

l=0l=1l=2Momentum distribution  spin-parity assignment of 13Be

l

=2

l

=1

l

=0

Example of momentum distribution

width of P distribution

depends on the orbital angular momentum of a knocked-out neutronSlide7

Experiment

7Slide8

Experimental Setup

Primary beam18O 100 MeV/uProduction targetBe　 6 mmPlastic scintillator1 mm 14BeEnergy : ~ 70MeV/uIntensity : ~8,000 counts/sPurity : 90%

RIPS

（

RI

KEN

P

rojectile-fragment

S

eparator)

8Slide9

Experimental Setup

14BePPACAngle of 14BeDipole magnetDrift chamber (FDC)Particle IdentificationDrift chamber (MDC)Angle of 12BeNaI(Tl) scintillatorg ray from 12Be

Reaction Target

Liquid

H

2

(227

mg/cm

2

)

charged particle

Hodoscope

(plastic

scintillator

)

Velocity of

12

Be

Neutron counter

(plastic scintillator)

Veto counter

12

Be

n

Detect

12Be and (a) neutron(s) in coincidence

~ 70

MeV

/u

9Slide10

Experimental Setup (photo)

Dipole MagnetTarget

Drift Chamber

He bag

Hodoscope

Neutron Detector

RIPS

Beam

10Slide11

Neutron

counterCharged particle VETO(thin plastic scintillators)Neutron counterBeam direction

~2m

Efficiency

For 1n detection

Neutron Counter

54bars

6x6x214cm

3

11Slide12

Relative energy spectrum (

12Be+n+n)Angular distributionResults (Inelastic scattering)p12Be

n

n

14

Be

12

Be

n

n

q

12

Be

n

n

14

Be(2

+

)Slide13

Inelastic scattering

14Be+p  14Be*  12Be+n+nSelect Mn=2 (detection multiplicity) crosstalk rejection (position, timing)Neutron Crosstalk Analysis

Two neutron event

Crosstalk

One neutron is detected by two (or more) detectors

Crosstalk

events

NEUT-B

NEUT-A

Same Wall event

Different

Wall event

13Slide14

Comparison with

14Be+C data (previous experiment)p(14Be,12Be+n+n)69 MeV/nucleonneutron crosstalk events are eliminatedefficiency and acceptance are correctedSimilar peak at around 0.3MeV was observedC(14Be,12Be+n+n)68

MeV

/nucleon

(previous exp.)

T. Sugimoto,

T. Nakamura,

Y. Kondo et al

PLB

654

,160 (2007)

14

Be(2

+

)

E

r

=0.28(1)

MeV

D

L=2

14Slide15

14Be+p experiment

DWBA analysisTwo optical potentials(A) A.A. Korsheninnikov et al. PLB343, 53 (1995)(B) R.L. Varner et al. Phys. Rep. 201, 57 (1991) (CH89)　　d =1.40(19) fm (14Be+p)p(14Be,12Be+n+n)69 MeV

/nucleon

14

Be(2

+

)

E

rel

(

12

Be+n+n) (MeV)

E

rel

=0.25(1)

MeV

s

=12.5±0.2±1.6

mb

(A)

(B)

p(

14

Be,

14

Be(2

+

) )69 MeV/nucleon

Y. Kondo, T. Nakamura, Y. Satou et

al.: to be submittedWidth is dominated by the experimental resolution

(~100keV (1s) @ 0.25MeV)

(1

s)15Slide16

2

+ energy & deformation length2+ energyLower than 12BeDeformation lengthSmaller than 12BeProton/neutron collectivities can be deduced (now in progress)

16Slide17

Phase space decay

14Be(21+)  12Be+n+nSequential Decay14Be(21+)　　 13Be+n (Erel=0.1MeV)　　 12Be+n+n (Erel=0.15MeV)

Decay of

14

Be(2

1

+

)

sequential

phase space

12

Be

n

n

E

c-n1

E

n-n

E

c-n2

E

c-(nn)

17Slide18

Relative energy spectrum (

12Be+n)Transverse momentum distributionsResults(One-neutron removal)p12Be

n

n

14

Be

12

Be

n

q

12

Be

n

13

Be

nSlide19

M

n=1 eventsSubtraction of Inelastic ComponentMn=1 eventsInelastic channelEstimated from Mn=2 eventsOne-neutron removal channel

Corresponds to

14

Be(2

+

)

One-neutron removal channel

(one neutron is emitted)

knocked out

Inelastic channel

(two neutrons are emitted)

not detected

two cases in

M

n

=1 events

inelastic component should be subtracted

19

p(

14

Be,

12

Be+n+n)

69

MeV

/nucleon

14

Be(2

+

)

E

rel

(

12

Be+n+n) (

MeV

)

E

rel

=0.25(1)

MeV

s

=12.5±0.2±1.6

mbSlide20

13

Be12Be+n+g13Be12Be(1-)+n(Eg=2.7MeV)13Be12Be(2+)+n(Eg=2.1MeV)s=11(2)

mb

(

E

rel

=0~4MeV)

s

=5.3(7)

mb

(

E

rel

=0~4MeV)

12

Be+n

s

=89(6)

mb

for

12Be+n+g is small

20Slide21

Two peaks at 0.5MeV,

2MeV Transverse momentum distribution (not longitudinal)Width of momentum distributions are different between peak regionsRelative Energy SpectrumErel(12Be+n) (MeV)p(14Be,

12

Be+n)

s

=89(6)

mb

(

E

rel

=0-4MeV)

0.25-0.75MeV

2.0-2.5MeV

P

x

resolution

~30MeV/c

21Slide22

Relative energy spectrump- and d-wave components

 Breit-Wigner shapes-wave component  G.F. Bertsch et al: PRC 57, 1366 (1998)Momentum distribution  CDCC calculation (by T. Matsumoto)13Be is assumed to be a core in 14Be13Be-p interactionJLM interaction J. Jeukenne et al.: PRC16, 80 (1977)n-p interactionR.A. Malfliet and J.A.Tjon NPA127, 161 (1969)13Be-n potentialWood-Saxon formDepth is adjusted to reproduce the separation energyFitting of Erel spectrum and momentum distributions

a :

Scattering length

22Slide23

0.5

MeV peak p-wave resonance2 MeV peak d-wave resonanceRelative Energy Spectrumps

d

p

s

d

E

rel

(

12

Be+n) (

MeV

)

p(

14

Be,

12

Be+n)

s

=89(6)

mb

(

E

rel

=0-4MeV)

0.25-0.75MeV

2.0-2.5MeV

23

p

d

sSlide24

p

-wave componentEr=0.50(1) MeVG=0.36(2) MeV consistent with Gsp (l=1)Jp=1/2-d-wave componentEr=2.48(7) MeVG=2.4(2) MeVlarger than

G

sp

(l=2)

other state @ 2MeV?

Relative energy spectrum

s

component

a

s

~ -3fm

d

state

E

r

=2.48(7)

MeV

Γ=2.4(2)MeV

p

state

Er

=0.50(1) MeV Γ=0.36(2)MeV

single particle width

p-wave @0.50MeV G

sp~0.5MeV d

-wave @2.48MeV Gsp~1.4MeV

24Slide25

Summary of the observed levels

The 2+ state in 14Be locates lower than the g.s. of 13BeSequential decay process is energetically forbidden25Slide26

The low-lying negative parity state

 Intruder stateLow-lying state of 13BeThiswork26Slide27

Shell

model calculationPSDMK D.J. Millener et al.: NPA255, 315 (1975)Provides the shell closure at 12BeSFO (spin-flip p-n monopole interaction) T. Suzuki et al.: PRC67, 044302 (2003)resonably reproduce the magicity loss at 12BeEnergy Levels of 12Be and 13Be13BePSDMK

Higher excitation energy of 1/2

-

SFO

Ground state of 1/2

-

 good!

several states at ~2MeV

Intruder 1/2- state

disappearance of N=8

magicity

 explained by spin-flip p-n monopole interaction

12

Be

13

Be

27Slide28

energy gap between [220 ½]

and [101 ½] orbitals disappears with large prolate deformationLarge quadrupole deformation (b~0.6) of 12Be H. Iwasaki et al. PLB481, 7 (2000)intruder 1/2- state of 13Be indicate large deformation?Deformation?

28

Ref) A. Bohr and B.R. Mottelson

Nuclear structure Vol.1Slide29

Breakup reactions (

14Be+p)Inelastic scattering2+ state of 14BePhase space decay of 2+ stateOne-neutron removal reactionLow-lying p-wave (intruder) resonance of 13BeSummary29