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Grupo de Física Nuclear Experimental G F E N CSIC I M E 15-21 January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC1 Hirschegg’06: Astrophysics and Nuclear.

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Presentation on theme: "Grupo de Física Nuclear Experimental G F E N CSIC I M E 15-21 January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC1 Hirschegg’06: Astrophysics and Nuclear."— Presentation transcript:

1 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC1 Hirschegg’06: Astrophysics and Nuclear Structure Low-Lying resonant states in 9 Be María José García Borge Århus-Göteborg-ISOLDE-Madrid-York Collaborations Outline: Motivation Asymmetries in A= 9 isobar Excited states in 9 Be accessible in the  -decay of 9 Li Summary and Outlook E exc ( 9 Be) QQ

2 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC2 Why study  -decay of Light Nuclei ?  “Exact” A-body calculations possible for A  12 reaching lowest energy states for I ≤ 9/2  Green Funtion Monte-Carlo methods  Non-core Shell-model  Asymetries in mirror beta transitions  The  (  n,  ) 9 Be + 9 Be( ,n) 12 C Competes with triple-  in n-rich scenarios  Importance of the  + n  5 He( ,  ) 9 Be  Experimentally  -decay provides  a clean way to feed unbound states  Break-up mechanism not fixed by kinematics

3 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC3 Mirror asymmetry principle and Systematics  - : n → p + e - + np ft -  + : p → n + e + + E.C. : p + e - → n + np ft +  Charge independence hypothesis of nuclear interactions  symmetry of analog  transitions  Isospin symmetry breaking   asymmetry in mirror  -decays Thomas et al., AIP Conf. Proc 681, p. 235 Systematics of experimental  values (A  40)  = 4.8 (4) %

4 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC4 A = 9 Isobar Nyman et al., NPA 510 (1990) 189Mikolas et al., PRC 37 (1988) 766 F. Ajzenberg-Selove, NPA 490 (1988) 1 Large asymmetries δ ≈ 3 δ=1.2±0.5 δ ≈ 0

5 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC5  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 9 Li n C- foil

6 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC6 9 B high excited states E p, ,  (keV) E sum (MeV) IAS Sequential Decay of 12.2 MeV State via 8 Be(gs), 8 Be(2 + ), 5 Li(gs) and 5 Li(1/2) R-Matrix-formalism applied. MC-simulations to account for efficiencies of each channel ResultsE: 12.19(4) MeV  : 450(20) keV J: 5/2 B GT : 1.20(15) U.C. Bergmann et al., Nucl. Phys. A692 (2001) 427 E sum (MeV)

7 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC7 Spin Determination for states in 9 Be Possible spins: 5/2  A 2 = /2  A 2 =0 1/2  A 2 =1 Fit of the angular distribution breakup  the 5 He(3/2 - ) channel Rev. Mod. Phys. 25 (1953) 729    n 5 He 9 Li 9 Be 3/2 - ?(-)

8 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC8 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/  = (15)% NP A692(2001)427PLB576 (2003)55 (1/2,5/2) - (1/2) - 3/2 -

9 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC9 5 He 8 Be(2 + ) Study of the 2.43 MeV, 5/2 - state in 9 Be R-Matrix formalism Tail through 5 He(gs) E*= E sum MeV E sum < 0.9 MeV 00.6 Hyper-spherical harmonics Bochkarev, Sov J. Nucl. Phys. 52 (1990) 964 E  (MeV) Be(gs) Fit Data Fit Data 0.3 E  (MeV) 0.3

10 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC10 Study of low lying levels 9 Be 8 Be(g.s.) 5 He 8 Be(2 + ) 0.9  E sum  1.3 MeV J = 1/ MeV level 6  E sum  7 MeV J = 5/2 (e,e’p) Unpbl. Tilley,NPA745(04) MeV Level

11 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC11 Contributions of the known  -fed levels of 9 Be  Sequential Decay  MeV State  8 Be(gs), 8 Be(2 + ), 5 He(gs), 5 He(1/2 - ), 8Be(4 + )  7.94 MeV State  5 He(gs), 8 Be(gs)  2.78 MeV State  8 Be(2 + ), 5 He(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

12 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC12 Is any other level of 9 Be contributing? 3  E sum  4 MeV J= 3/2 1.8 E   E sum  1.8 E  E level = 5.0(5) MeV,  = 2.0(2) MeV

13 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC13 Candidates in the literature? E level = 5 MeV,  = 2 MeV, J = 3/2 - E level = 5.6(1) MeV,  = 1.33(36) MeV, J = 3/2 - Dixit et al., Phys. Rev. C 43(91) MeV Shell Model Mikolas et al., PRC 37 (1988) 766

14 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC14 Fit alpha spectrum from 9 Li decay New Level Singles Langevin et al.,Nucl. Phys. A366 (1981) 449 Nyman et al., Nucl. Phys. A510 (1990) 189

15 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC15 Summary & Outlook The low lying resonance states in 9 Be have been investigated via  -delayed particle emission from 9 Li. 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=5/2 for the 7.94 MeV Confirmation of broad 3/2 - state at 5 MeV,  = 2 MeV Evidence of the contribution of decay via 5 He(g.s.) FUTURE:  Break up of the 2.43 MeV level in 9 Be  11 Li: Disentangle the breakup of the 18.1 MeV state in 11 Be  Comparison of B GT distribution between 11 Li and its core 9 Li The beta-decay asymmetry in the A= 9 isobar system studied for the gs and high excited (  12 MeV) states in 9 Be & 9 B 12MeVSequential 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

16 Grupo de Física Nuclear Experimental G F E N CSIC I M E January 2006, Hirschegg, AustriaM.J.G. Borge, IEM CSIC16 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


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