beta-decay directly to continuum k riisager dept. of physics and astronomy aarhus university
TRANSCRIPT
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)