1. Measurement of the b-branch of 12B to the Hoyle state in 12C
Hans Fynbo replacing
Martin Alcorta
Physics Division
Argonne National Laboratory
INPC 2013
Firenze, Italia

2. Motivation
12C 3a 0+
12B 1+
b-decay
(0+, 1+ or 2+) 2+
1.28%
97.2% gs
4.439
7.654
Recent studies using beta-decay get a result half that of the literature value for the branching ratio to the Hoyle state
It is crucial to get the correct feeding to the states in R-matrix calculations, which found evidence for 2+ in 12C at 11.1 MeV
0.8%
0+/2+
1.2%
F. Ajzenberg-Selove, NPA506, 1 (1990)
S. Hyldegaard, PRC81, (2010)
M. Alcorta
6/3/2013

3. 12C Motivation 12B 0.58(2)% 1.2(3)% 1.2% 1.28(4)% KVI Literature 97.2%0+
12B 1+
b-decay
(0+, 1+ or 2+) 2+
1.28(4)%
97.2% gs
7.654
KVI
Literature
0.58(2)%
1.2(3)%
1.2%
4.439
0.068%
0.08%
2.8×10-4%
Nature2005 PRC2009,2010, PLB2009
M. Alcorta
6/3/2013

4. Confirm BR(7.65) using independent method
b-decay
(0+, 1+ or 2+) 1+
12B
0.58(2)%
1.2(3)%
7.654 0+ 3a
1.28(4)%
0.0413(11)%
4.439 2+
97.2% gs 0+
12C
M. Alcorta
6/3/2013

5. Confirm BR(7.65) using independent method3a 0+
12B 1+
β-decay
(0+, 1+ or 2+) 2+
1.28%
97.2%
0.58%
1.2% gs
7.654
g3%
0.58(2)%
1.2(3)%
b 5%
1.28(4)%
4.439
gg 0.1%
g 3%
D. E. Alburger, Phys. Rev. 131, 1624 (1963).
M. Alcorta
6/3/2013

6. Confirm BR(7.65) using independent method3a 0+
12B 1+
b-decay
(0+, 1+ or 2+) 2+
1.28%
97.2%
0.58%
1.2% gs
7.654
bgg
1.7(5)%
0.58(2)%
1.2(3)%
1.28(4)%
4.439 gg
M. Alcorta
6/3/2013

7. Need to reduce Bremsstrahlung!
Experiment
Gammasphere at ATLAS
101 high-purity Ge detectors
BGO Compton-suppression shields
2.5 pnA 11B beam, 40 MeV
Thick TiD2 target to stop the beam
1.5 mg/cm2 D2
Measure 40 ms beam on/beam off
T1/2 = 20.2 ms
Qb = MeV
Need to reduce Bremsstrahlung!
M. Alcorta
6/3/2013

8. Confirm BR(7.65) using independent method
Unused Bonner sphere
Made from CH2
Low Z for reducing Bremsstrahlung
Also good at absorbing gammas
+ Attenuate low-energy gammas
- Need to determine absolute efficiency
Efficiency determined from
24Mg 4+ -> 2+ -> 0+ transition
Gives absolute efficiency at 1.32 MeV
Relative efficiency determined from 56Co and 152Eu sources
Brad DiGiovine
M. Alcorta
6/3/2013

9. Results
Standard GS chamber
With plastic housing
M. Alcorta
6/3/2013

10. 12C Results 12B 1.28% 97.2% 0.58% 1.2% 0.58(2)% 1.2(3)% 1.28(4)% 1+3a 0+
12B 1+
b-decay
(0+, 1+ or 2+) 2+
1.28%
97.2%
0.58%
1.2% gs
7.654
0.58(2)%
1.2(3)%
1.28(4)%
4.439
M. Alcorta
10/25/2012

11. Preliminary Results BR(7.65) = 0.68(09)%
The error is dominated by statistics
Increase statistics using HfD2 target
Can we determine Gg / G ?
Gg / G = 4.12(11)x10-4
BR(4.44) = 1.28(4)%
ε3.21 = 2.94(9)%
Cq = 1
Preliminary
F. Ajzenberg-Selove, Nucl. Phys. A506, 1 (1990)
M. Alcorta
6/3/2013

12. Determine Radiative WidthGg Gp
Q2= -287 keV
a +8Be
Hoyle state
Q1 = -92 keV
a + a
M. Alcorta
6/3/2013

13. Determine Radiative Width
Quantity
Value
Error(%)
Q3a
379.4(2)keV
1.2
Grad/G
4.12(11) ×10-4
Markham, Austin,
Gp/G
6.7(6) × 10-4
Alburger 1977 Gp
62.3(2.0) meV
Chernykh 2010
Shahabuddin 1976
NPA , (1976)
PRC 16, 2394 (1977).
PRL , (2010)
M. Alcorta
6/3/2013

14. Conclusion / Outlook Determined value of BR to Hoyle state as 0.68(9)%
In agreement with recent results from b-decay
Confirms a 2+ at 11.1 MeV in 12C from b-decay
Disagreement with literature value
Method could possibly be used to constrain Gg/ G
b-decay result for mirror nucleus 12N is 1.41(3)%
Previous value 2.7(4)%
Use same method to independently determine BR(7.65) for 12N?
M. Alcorta
6/3/2013

15. Thank you Aarhus University, Aarhus, Denmark
Physics Division, Argonne National Laboratory, Argonne, IL
Western Michigan University, Kalamazoo, MI
Department of Astronomy and Astrophysics, University of Chicago, IL
Joint Institute for Nuclear Astrophysics, Chicago, IL
Laboratorio Tandar, Buenos Aires, Argentina
H.O.U Fynbo, K.L. Laursen, M. Albers, S. Almaraz-Calderon, P.F Bertone, P.F.F. Carnelli,
M.P. Carpenter, B. DiGiovine, J.P. Greene, C.R Hoffman, R.V.F Janssens, T. Lauritsen,
C. Nair, S.T. Marley, K.E. Rehm, D. Seweryniak, C. Ugalde, S. Zhu
M. Alcorta
6/3/2013 15

16. EXTRAS
M. Alcorta
6/3/2013 16

17. 12C Motivation 12B R-matrix analysis (multi-channel, multi-level):2+ 0+
12C 3a 0+
12B 1+
b-decay
(0+, 1+ or 2+) 2+
1.28%
97.2% gs
4.441
7.654
0.04%
Beta-decay Scattering:
E(0+) = 11.2(3) MeV (3) MeV
G(0+)= 1.5(6) MeV (8) MeV
Beta-decay Scattering:
E(2+) = 11.1(3) MeV (2) MeV
G(2+)= 1.4(4) MeV (2) MeV
R-matrix analysis (multi-channel, multi-level):
M. Alcorta
6/3/2013

18. Lowest 2+ resonance in 12C? E(2+)=9.8(2) MeV G(2+)=0.8(2)MeV 3- 1- 3a
Stellenbosch: Freer et al. (2009): 12C(p,p´)12C
Yale : Zimmerman et al. (2011): 12C(p,p´)12C 3- 1-
Osaka: Itoh et al. (2011): 12C(, ´)12C
Lowest 2+ resonance in 12C? 3a
E(2+)=9.8(2) MeV
G(2+)=0.8(2)MeV
Fynbo & Freer, Physics, 4 (2011) 94.
M. Alcorta
6/3/2013