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15-21 January 2006, Hirschegg, Austria M.J.G. Borge, IEM CSIC 1

Hirschegg’06: Astrophysics and Nuclear Structure

Low-Lying resonant states in 9Be

María José García Borge

Århus-Göteborg-ISOLDE-Madrid-York Collaborations

Outline:

Motivation

Asymmetries in A= 9 isobar

Excited states in 9Be accessible in the -decay of 9Li

Summary and Outlook

Eexc (9Be)Q

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Why study -decay of Light Nuclei ?

“Exact” A-body calculations possible for A12

reaching lowest energy states for I ≤ 9/2

Green Funtion Monte-Carlo methodsNon-core Shell-model

Asymetries in mirror beta transitions

The (n,)9Be + 9Be(,n)12CCompetes with triple- in n-rich scenarios

Importance of the + n 5He(, )9Be

Experimentally -decay providesa clean way to feed unbound statesBreak-up mechanism not fixed by kinematics

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Mirror asymmetry principle and Systematics

- : n → p + e- +

n p

ft-

+ : p → n + e+ +

E.C. : p + e- → n +

n p

ft+

Charge independence hypothesis of nuclear interactions symmetry of analog transitions

GTAFV BgBg

Kft

22

sg

KV

)6(61462 )3(587.12

2

V

A

gg

1

ft

ft

Isospin symmetry breaking asymmetry in mirror -decays

Thomas et al., AIP Conf. Proc 681, p. 235

Systematics of experimental values (A40)

= 4.8 (4) %

1

GT

GT

B

B

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15-21 January 2006, Hirschegg, Austria M.J.G. Borge, IEM CSIC 4

A = 9 Isobar

Nyman et al., NPA 510 (1990) 189 Mikolas et al., PRC 37 (1988) 766

F. Ajzenberg-Selove, NPA 490 (1988) 1

Large asymmetries 1

)(

)(

ft

ft

δ ≈ 3

δ=1.2±0.5

δ ≈ 0

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ISOL method

point-like pure sources

-decay to populate state of interest

clean and selective

Use DSSSDs for complete kinematics

Large solid angle (rare events)

High Segmentation (avoid summing)

Effective Readout

Experimental technique for multiparticle detection

9Li

n

C-foil

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15-21 January 2006, Hirschegg, Austria M.J.G. Borge, IEM CSIC 6

9B high excited states

)2(for (9/8) MeV 0.3

)2/3(for (9/5) MeV 2

)0(for (9/8) keV 92

M

MM

8

5

8

firstrecoiling

firstrecoilingsum

Be

Li

Be

xEE

Ep,,(keV)

Esu

m

(MeV

)

IAS•Sequential Decay of 12.2 MeV State via 8Be(gs), 8Be(2+), 5Li(gs) and 5Li(1/2)

•R-Matrix-formalism applied.

•MC-simulations to account for efficiencies of each channel

•Results E: 12.19(4) MeV

: 450(20) keV

J: 5/2

BGT: 1.20(15)U.C. Bergmann et al., Nucl. Phys. A692 (2001) 427

Esu

m(M

eV

)

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Spin Determination for states in 9Be

)1)(cos3(2

11)( 2

2 AW

Possible spins:

5/2 A2=-0.7143/2 A2=01/2 A2=1

Fit of the angular distribution breakup the 5He(3/2-) channelRev. Mod. Phys. 25 (1953) 729

n5He

9Li9Be3/2-

3/2-

?(-)

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15-21 January 2006, Hirschegg, Austria M.J.G. Borge, IEM CSIC 8

A = 9 Isobar

Nyman et al., NPA 510 (1990) 189Mikolas et al., PRC 37 (1988) 766

F. Ajzenberg-Selove, NPA 490 (1988) 1

δ ≈ 3

δ=1.2±0.5

δ ≈ 0

= 3.4(7)

= 0.032(3)

5/2-

5/2-

13.257

=0.45

54.1(15)%

NP A692(2001)427

PLB576 (2003)55

(1/2,5/2)-

(1/2)-

3/2-

3/2-

3/2-

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15-21 January 2006, Hirschegg, Austria M.J.G. Borge, IEM CSIC 9

5He 8Be(2+

)

Study of the 2.43 MeV, 5/2- state in 9Be

R-Matrix

form

alism

Tail through 5 He(gs)

E*= Esum + 1.57 MeV

Esum < 0.9 MeV

0 0.6

Hyper-spherical harmonics

Bochkarev , Sov J. Nucl. Phys. 52 (1990)

964

E (MeV)0 0.6

8Be(gs)

Fit

Data

Fit

Data

0.3

E (MeV)0.3

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Study of low lying levels 9Be

8Be(g.s.)

5He 8Be(2+)

0.9 Esum 1.3 MeV

J = 1/2

2.78 MeV level

6 Esum 7 MeV

J = 5/2(e,e’p) Unpbl.

Tilley,NPA745(04)155

7.94 MeV Level

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15-21 January 2006, Hirschegg, Austria M.J.G. Borge, IEM CSIC 11

Contributions of the known -fed levels of 9Be

Sequential Decay

11.81 MeV State 8Be(gs), 8Be(2+), 5He(gs), 5He(1/2-), 8Be(4+)

7.94 MeV State 5He(gs), 8Be(gs)

2.78 MeV State 8Be(2+), 5He(gs)

2.48 MeV state (Bocharev et al., Sov. J. Nucl. Phys. 52(90)964)

R-Matrix-formalism applied.

MC-simulations to account for efficiencies of each channel

E, MeV

Missing Intensity

Incoherent sum of all channels

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15-21 January 2006, Hirschegg, Austria M.J.G. Borge, IEM CSIC 12

Is any other level of 9Be contributing?

3 Esum 4 MeV

J= 3/2

1.8 E1 + 0.7 Esum 1.8 E1 + 1.1

Elevel = 5.0(5) MeV, = 2.0(2) MeV

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Candidates in the literature?

Elevel = 5 MeV, = 2 MeV, J = 3/2-Elevel = 5 MeV, = 2 MeV, J = 3/2-

Elevel = 5.6(1) MeV, = 1.33(36) MeV, J = 3/2-

Dixit et al., Phys. Rev. C 43(91)1758

(p,p’) @ 180 MeV Shell Model

Spin E*(9Be) (MeV)

β-decay BGT

Reference

3/2- 5.09 0.005 Cohen-Kurath (6-16)BME (1965)

4.87 0.069 Millener 5.49 0.014 Kumar (1974) 4.66 0.081 Cohen-Kurath (8-16) POT

(1965) 5/2- 7.48 0.140 Cohen-Kurath (6-16)BME

7.66 0.004 Millener 6.91 0.010 Kumar (1974) 7.39 0.032 Cohen-Kurath (8-16) POT

(1965)

Mikolas et al., PRC 37 (1988) 766

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15-21 January 2006, Hirschegg, Austria M.J.G. Borge, IEM CSIC 14

Fit alpha spectrum from 9Li decay

New

Level

Singles

E*(9Be) (MeV)

Ip (keV) B.R. (%)

Coinc Singles Langevin Nymang.s. 3/2- 49.2±0.9 49.2±0.9 50.5±5 50±32.43 5/2- 0.77 ±0.15 29.6 ±1.3 31.9 ±3.4 34±4 30±32.78 1/2- 1080±110 15.7±0.8 11.6±2.2 10±2 16±35.0 3/2- 2000±500 3.2±1.0 3.15±0.4

7.94 5/2- ~1000 0.68±0.12 1.5±0.4 1.5±0.5 <211.81 5/2- 400±30 1.62±0.07 2.7±0.4 2.7±0.2

Langevin et al.,Nucl. Phys. A366 (1981) 449

Nyman et al., Nucl. Phys. A510 (1990) 189

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Summary & Outlook

The low lying resonance states in 9Be have been investigated via -delayed particle emission from 9Li.

Angular correlations used for firm spin determination First exp. determination of the J=1/2 character of 2.78 MeV

StateFirm assignment of J=5/2 for the 7.94 MeV

Confirmation of broad 3/2- state at 5 MeV, = 2 MeVEvidence of the contribution of decay via 5He(g.s.)

FUTURE: Break up of the 2.43 MeV level in 9Be11Li: Disentangle the breakup of the 18.1 MeV state in 11Be

Comparison of BGT distribution between 11Li and its core 9Li

The beta-decay asymmetry in the A= 9 isobar system studied for the gs and high excited ( 12 MeV) states in 9Be & 9B

12MeV Sequential breakups for p and n Confirmed large asymmetry = 3.4 (1.0)

Beta asymmetry to the g.s. negligible must be due to differences in the structure of the two final state resonances

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15-21 January 2006, Hirschegg, Austria M.J.G. Borge, IEM CSIC 16

Collaborators

Århus University

C.Aa. Diget

H.O.U. Fynbo

H. Jeppesen

K. Riisager

U. Bergmann

Chalmers Univ of Technology

B. Jonson

M. Meister

G. Nyman

T. Nilsson

K. Wilhelmsen

Inst. Estructura de la Materia

L.M. Fraile

Y. Prezado

O. Tengblad

University

of York

B.R. Fulton