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Beta-decay directly to continuum

Beta-decay directly to continuum. K Riisager Dept. of Physics and Astronomy Aarhus University. Beta-delayed deuterons. Q βd = 3007 keV – S 2n Jonson, Riisager, NPA693 (01) 77 6 He, low branch several exp: Raabe et al,PRC80 (09) 054307 theory: directly to continuum states

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Beta-decay directly to continuum

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  1. Beta-decay directly to continuum K Riisager Dept. of Physics and Astronomy Aarhus University

  2. Beta-delayed deuterons • Qβd = 3007 keV – S2nJonson, Riisager, NPA693 (01) 77 • 6He, low branch several exp: Raabe et al,PRC80 (09) 054307 theory: directly to continuum states • 11Li, again pointing to direct transitions Raabe et al, PRL 101 (08) 212502

  3. Why continuum transitions ? • Alternative: through resonances in daughter • obvious for narrow peaks, not for broad features • may give “unphysical/unnatural” interpretation • I.e.: when do resonances “cover everything” ? • Non-resonant continuum states, cf. Berggren (NPA109 (68) 265 etc) Need to define (fit-)procedures carefully

  4. ..the world according to R-matrix • Inner and outer space • refs: Lane and Thomas, RMP 30 (58) 257 • Descouvemont and Baye, RPP 73 (10) 036301 • Complete basis internally • can describe direct reactions • “no scattering” Wigner, Eisenbud, PR72 (47) 29 R-matrix levels ≠ resonances • Adapted to β-decay by Barker • employed here for A=8,12 www.am.qub.ac.uk 8Be 2+ resonance at 3 MeV plays a key role

  5. Example: 8B decay • Decade-long discussion on interpretation, e.g. Barker, Aust.J.Phys. 42 (89) 25 - Bhattacharya, Adelberger, PRC65 (02) 055502 • “Intruder” 2+ below/above 16 MeV doublet ? • New data from JYFL (and KVI) Poster: T. Roger

  6. 8B fits – preliminary results 1 16 MeV 3 MeV Spectrum corrected for phase space and penetrability

  7. 8B fits – preliminary results 2 Fits with 3 MeV resonance, the 16 MeV doublet and one extra 2+ level (not yet satisfactory description).

  8. Example: 12N and 12B decay 12N 12B Data from JYFL and KVI 12C 8Be 2a

  9. Results  12N 12B Phys. Lett. B 678 (2009) 459

  10. Models including max. three unbound states Sum spectra (KVI) 12N components (JYFL) c2/df 281 15.9 44.8 3.24 6.06 18.4 12N 8Be peak 8Be excited states 12B

  11. Four unbound states Two 0+, two 2+ c2/df = 1.65 Three 0+, one 2+ c2/df = 1.24

  12. JYFL data, Dalitz plots Detailed analysis: at 10.5-11.7 MeV 2+/tot ≈ 0.3 above 12.7 MeV 2+ dominates C.Aa. Diget et al, PRC80 (09) 034316

  13. Three 0+, two 2+ states c2/df = 1.21 3 0+, 1 2+ 2 0+, 2 2+ Phys. Rev. C 81, 024303 (2010)

  14. A=12 summary • Two (new) resonances in 12C: • 0+ at 11.2(3) MeV, Γ = 1.5(6) MeV • 2+ at 11.1(3) MeV, Γ = 1.4(4) MeV • Higher lying 0+ and 2+ strength • position depends on channel radius • width/BGT values unrealistic (100 MeV/50, 1 MeV/5 – only room for BGT of 1 from sum rule for T=0) • Direct decay to continuum ?! • acceptable fits with “R-matrix continuum” BGT = 0.6

  15. A (very) simple model • Beta-decay gives Oβ|i> -- a Gaussian/Yukawa • Final two-body state with no interaction, i.e. by construction: decay only to continuum • Fits: “normal” resonances…. E/ħω E/Sn

  16. Final comments • Not a new discovery (reaction exp, low+high E, radiative capture) • Most likely (?) not just light nuclei • Part of the GTGR ? ! (for some nuclei) • Pronounced effects for halo nuclei F + GT • Technically more complex calculations (? due to coexistence with decays to resonances)

  17. Many thanks to: collaborators in experiments at ISOLDE JYFL KVI my close coworkers Hans Fynbo Solveig Hyldegaard ** Aksel Jensen Oliver Kirsebom Special acknowledgment to Fred Barker

  18. R-matrix Phys. Rev. C 81, 024303 (2010)

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