Beta-decay directly to continuum

K RiisagerDept. of Physics and Astronomy

Aarhus University

• Qβd = 3007 keV – S2n Jonson, Riisager, NPA693 (01) 77

• 6He, low branch several exp: Raabe et al,PRC80 (09) 054307

theory: directly to continuum states

• 11Li, again pointing todirect transitionsRaabe et al, PRL 101 (08) 212502

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) 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

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

8B fits – preliminary results 1

Spectrum corrected for phase space and penetrability

3 MeV

16 MeV

8B fits – preliminary results 2

Fits with 3 MeV resonance, the 16 MeV doublet and oneextra 2+ level (not yet satisfactory description).

12B12N

12C 8Be 2

Example: 12N and 12B decay

Data from JYFL and KVI

12N

12B

12N 12BE (MeV) Lit. Exp. Lit. Exp.

g.s. 94.6(6) 96.03(5) 97.2(3) 98.03(5)

4.44 1.90(3) - 1.28(4) -

7.65 2.7(4) 1.41(3) 1.2(3) 0.58(2)

9-12 0.46(15) 0.404(9) 0.08(2) 0.068(3)

12.71 0.28(8) 0.119(3) - 2.8(2)*10-4

12-16.3 - 0.020(3) - -

15.11 3.8(8)*10-3 3.2*10-5* - -

7.3-16.3 3.4(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) 12N components (JYFL)

12N

12B

8Be peak

8Be excited states

28115.944.83.246.0618.4

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 10.5-11.7 MeV 2+/tot ≈ 0.3

above 12.7 MeV 2+ dominates

C.Aa. Diget et al, PRC80 (09) 034316

Three 0+, two 2+ statesdf = 1.21

3 0+, 1 2+ 2 0+, 2 2+

Phys. Rev. C 81, 024303 (2010)

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

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

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, 024303 (2010)