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

Q βd = 3007 keV – S 2n Jonson, Riisager, NPA693 (01) 77 6 He, low branch several exp: Raabe et al,PRC80 (09) theory: directly to continuum states 11 Li, again pointing to direct transitions Raabe et al, PRL 101 (08) Beta-delayed deuterons

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

..the world according to R-matrix Inner and outer space – refs: Lane and Thomas, RMP 30 (58) 257 – Descouvemont and Baye, RPP 73 (10) 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, Be 2 + resonance at 3 MeV plays a key role

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

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

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

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

12 N 12 B 12 N 12 B E (MeV)Lit.Exp.Lit.Exp. g.s.94.6(6)96.03(5)97.2(3)98.03(5) (3)-1.28(4) (4)1.41(3)1.2(3)0.58(2) (15)0.404(9)0.08(2)0.068(3) (8)0.119(3)-2.8(2)* (3) (8)* *10 -5 *   (4)2.10(3)1.3(3)0.69(2) Results Phys. Lett. B 678 (2009) 459 

Models including max. three unbound states Sum spectra (KVI) 12 N components (JYFL) 12 N 12 B 8 Be peak 8 Be excited states    df

Two 0 +, two 2 +    df = 1.65 Three 0 +, one 2 +    df = 1.24 Four unbound states

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

Three 0 +, two 2 + states    df = , , Phys. Rev. C 81, (2010)

A=12 summary Two (new) resonances in 12 C: – 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/B GT values unrealistic (100 MeV/50, 1 MeV/5 – only room for B GT of 1 from sum rule for T=0) Direct decay to continuum ?! – acceptable fits with “R-matrix continuum” B GT = 0.6

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

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 )

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

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