nilsson model 50 years

Grupo de Física Nuclear

Experimental

GFE

N

CSICI

ME

Lund, Sweden 14-18 june 2005

M.J.G. Borge IEM, CSIC 1

Nilsson Model 50 years

Low-Lying resonant states in the 9Be continuum

María José García Borge

Århus-Göteborg-ISOLDE-Madrid-York Collaborations

Outline:

Motivation

Experimental Tools & Analysis Methods

Excited states in 9Be E < 9 MeV

Summary and Outlook


Experimental

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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

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

Importance of the +n5He(, )9Be

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


Experimental

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Break-up to multi-particle final states

Characteristics Kinematics not fixed by conservation laws

The mechanism of X->Y can be studied sequential, simultaneous, democratic...

Need complete kinematics measurement to fully characterise final state

Connection to level structure closer for direct break-up.

Y

E,

X Y

E,

X Y

E,

X

Sequential

Direct

?


Experimental

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A = 9 Isobar

Nyman et al., NPA 510 (1990) 189 Mikolas 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

(1/2,7/2)-

(1/2)-

(3/2)-

(3/2)-


Experimental

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ISOL method

-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


Experimental

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Analysis Method

Precise determination of the source position

The radioactive beam is completely stopped in the thin carbon foil it decays at rest linear momentum conservation

The uncertainties coming from the finite size of the pixel

PΔPPPPP 321fi

MeV/c3020PΔ0,PΔ maximum

Triple coincidencesIdentification of particles

Removal of beta contamination

Double coincidences Reconstruction of the third particle

P1+ P2+ P3=0 less precise


Experimental

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Beta Filters

The beta particle taken as an alpha wrong reconstruction beta filters needed

•Anticoincidences with the back detectors

•|Efront-Eback|<100 keV

•A cut in the total linear momentum

ΔP<30 MeV/c

•E(deposited) > 200 keV

n n

n

n


Experimental

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Double coincidences in 9Li decay

)(0 2121 PPPPPP nn

E*(9Be) = Esum + 1.57 MeV (n breakup)

9Li beam @ 20 keV

Ultra-thin entrance window Detectors

Tengblad et al., NIMA525 (2004)458


Experimental

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Study of the 2.43 MeV state in 9Be

9Li beam 20 keV

40 g/cm2 C-foil

R-Matrix

form

alism

Tail through 5 He(gs)

E*= Esum + 1.57 MeV

Esum < 0.9 MeV

E (MeV)0 0.6

Hyper-spherical harmonics

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

964

E (MeV)0 0.6


Experimental

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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-

?(-)


Experimental

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Study of low lying levels 9Be5He

8Be(g.s.)

8Be(2+)

0.9 Esum 1.3 MeV

J = 1/2

2.78 MeV level

6 Esum 7 MeV

J = 5/2(p,p’) data PRC43(91)1758

7.94 MeV Level


Experimental

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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


Experimental

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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


Experimental

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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)


Experimental

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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


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Summary & Outlook

Beta-delayed multi-particle emission is a powerful tool

If study in full kinematicsDecay mechanismE, , spin...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 State

Firm assignment of J=7/2 for the 7.94 MeVConfirmation of broad 3/2- state at 5 MeV, = 2

MeVEvidence of the contribution of decay via

5He(g.s.)

FUTURE: Break up of the 2.34 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


Experimental

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Collaborators

Århus University

C.Aa. Diget

H.O.U. Fynbo

H. Jeppesen

K. Riisager

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


Experimental

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Calculation of B(GT) for the 11.81 MeV level in 9Be

Normalisation. n(4.5-5.5) = (30±3) x10-4

Corrections:

0.335 of in (4.5-5.5) MeV

Energy dependence of “f” (1.1)

Part of 11.81 Mev peak out of the range (0.76)

-singles from 9Li decay

BBGTGT= 5.3 = 5.3 ± 0.9± 0.9

BGT =5.6 ± 1.2 Nyman et al., NPA 510 (1990) 189


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Comparison of 9Li & 9C decays

•There is no asymmetry in the beta-decay of 9C and 9Li to the ground states of 9Be and 9B.•With respect to the mirror transitions to the high energy region

9Be 9B

Energy 11.81(0.15) MeV a 12.19 (0.04) MeV

Width 400(30) keV a 450 (20) keV

Spin 5/2- 5/2-

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

Same spin and same widthSame spin and same width


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9B excitation energy

)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 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)

Bergmann et al., NPA692 (2001) 427


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Beta feeding to the 11-12 MeV region in 9Be Fit of the high energy peak gating on

the 5He(3/2-) channel

11.81 MeV state 91±10%11.28 MeV state 9 %(e,p)-scattering on 9Be assumed J = 7/2

Only the participation of the 11.81 MeV state in 9Be for the beta feeding is

considered

-emission 5He(gs)-channel


Experimental

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Asymmetry in the A=9 isobars

Sequential decay

open channels

MC-Simulations

Geometrical eff. & angular correlations

9C 9B (12.19 MeV, 5/2) B(GT) = 1.20 (15) / 1.58(16) [PRC61(2000) 064310]

8Be(0+) + p 8Be(2+) + p 8Be(4+ ) + p 5 He(3/2-)+ 5 He(1/2-) + Ref

0.090 (10)0.085 (14)

0.25 (7) 0.18 (3)

- 0.60 (7) 0.74 (8)

0.06 (4) This work, NPA 692(2001)427 - PRC61(2000)

8Be(0+) + n 8Be(2+) + n 8Be(4+ ) + n 5 He(3/2-)+ 5 He(1/2-) +

0.02(0.01) 0.11(0.06) 0.12(0.08) 0.28(0.06) 0.47(0.07) This work

Y. Prezado, Phys. Lett B576 (2003) 55

9Li 9Be (11.8 MeV, 5/2) B(GT) = 5.3 (9)

nilsson model 50 years

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