1. 12C(a,g)16O thermonuclear reaction rate: present status and perspectives
Problematics
Present status
Perspectives
A. Lefebvre-Schuhl
CSNSM Orsay
December 14th 2007
ESF-Athens
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14

2. Helium burning Influence on: [C]/[O]
12C+4He
16O 0+
9.64
7.65
4.44 3- 2+
(7.16) 2- 1-
6.05
6.13
6.92
7.12
8.87
9.59
12C+4He O
Helium burning
3  C
Influence on:
[C]/[O]
Further hydrostatic burning stages
Final states of stars
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14

3. (g-ray angular distributions)
12C (a, g) 16O
T ~ 0.2 x 109 K
 E(Gamow peak) ~ 300 keV
(300 keV)  barn !
Reaction rates
 Extrapolation :
R- or K-matrix formalism
Microscopic cluster models
For each contribution: capture to the
ground state and to excited states
E2 : Direct capture
E1 : large 1- subthreshold resonance
level below the reaction threshold
+ 2+ level below the reaction threshold
Need of E1, E2 for E*  ground state
(g-ray angular distributions)
A. Lefebvre-Schuhl
and for E*  excited state
ESF-Athens 2007/12/14

4. Indirect methods : b-delayed a-decay of 16N 16O Coulomb breakup
Transfer reaction, ANC method
Trojan-horse method
b-delayed p-decay of 17Ne
Indirect methods :
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14
R: 79  21 keVb
K: 82  26 keVb
SE1(300)
16N → b- + 16O → a + 12C
Azuma et al. Phys. Rev. C 50, (1994) 1194

5. Direct methods in direct kinematics:
a-beam, 12C target
g-ray angular distribution : in a few steps (turn table)
simultaneously (4p-array)
Intense a-beam : up to 700 pmA (Stuttgart dynamitron)
pulsed a-beams (Tokyo, Karlsruhe)
12C targets: isotopically pure and resistant to a-beams :
12C implantation
efficient water cooling
sophisticated g-ray arrays:
angular distribution,
background suppression: shieldings
or coincidences with pulsed beams
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14

6. g-ray angular distributions :
in a few steps: turn table (as Kunz et al, Fey et al...)
simultaneously: 4p-array (as Assunçao et al)
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14
« Eurogam » setup
Ex : Assunçao et al. PRC 73 (2006) :
g-ray angular distribution at 9 different angles simultaneously with 9 HP-Ge detectors
 very good energy resolution
Ecm eff = MeV
Compton suppression
(active BGO shields)
Total g efficiency at 10 MeV :
1.2x10-3 in experimental conditions
( at 1.33MeV)

7. Present SE1 results to the ground state
R-matrix fits of
a-scattering data
b-delayed a-decay of 16N
the radiative capture data
taking into account 3 levels
 4 interference combinations
Hammer et al.
Nucl. Phys. A758 (2005) 363
Best -> SE1(300) = 7717 keVb c2
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14

8. Present SE2 results to the ground state
R-matrix fits of
a-scattering data
the radiative capture data
taking into account 5 levels
 16 interference combinations
Best -> SE2(300) = 81  22 keVb c2
Hammer et al.Nucl. Phys. A758 (2005) 363
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14

9. Cascades and Stot SE1, SE2 to ground state and the others :
g-cascades through:
6.05, 6.92, 7.12 MeV levels
High g-ray background:
Up to 2006, only based on intensities of the 6.92 MeV and 7.12 MeV or both together
g-ray considered as giving the cascade amount:
 only an upper limit
Results obtained either in direct or inverse kinematics

10. Cascades to the 6.92 and 7.12 MeV levels
Redder et al. Nucl.Phys. A462, 385 (1987)
6.92
x : Kettner et al.
Z. Phys. A 308 (1982) 73
- : Redder et al.
Nucl.Phys. A462, 385 (1987)
Buchmann& Barnes
Nucl. Phys. A777 (2006) 254
S6.9(300) =7 keVb
S6.9(300) =7+13 keVb -4
S7.1(300) = 1.3 keVb
A. Lefebvre-Schuhl
FINUSTAR /09/12

11. Direct methods in inverse kinematics:
12C-beam, 4He-gas target
12Cn+
16Om+
g-ray detection
16O-recoil measurement
Ecm=2.0 MeV
s ≈ 10 nb
16O
DE-E
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14
European Recoil Separator for Nuclear Astrophysics

12. Thanks Schürmann, Kunz, Strieder et al.
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14
ERNA‘s data
Schürmann et al. EpJ A 26 (2005) 301
Thanks Schürmann, Kunz, Strieder et al.
E1, E2,
cascades
( )
and total contributions
R-Matrix calculation
Kunz et al. Ap.J. 567 (2002) 643
E1 and E2 data
Assunçao et al. PRC 73(2006)055801
and Fey et al. to be published

13. Detector of Recoils and Gammas of Nuclear reactions
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14
g-array: BGO
Detector of Recoils and Gammas of Nuclear reactions

14. Cascades to the 6.045 MeV level
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14
Cascades to the MeV level
Matei et al. PRL 97 (2006)
DRAGON TRIUMF
S6.0(300) = keVb
-15
Detector of Recoils and Gammas of Nuclear reactions

15. Thanks Kunz, Strieder et al.
A. Lefebvre-Schuhl
ESF-Athens 2007/12/14
ERNA‘s data
Schürmann et al. EpJ A 26 (2005) 301
Thanks Kunz, Strieder et al.
Preliminary results : new R-matrix calculation, Kunz et al.
Preliminary results : new R-matrix calculation, Kunz et al.

16. 3 R-matrix calculations S(300)
A. Lefebvre-Schuhl
FINUSTAR /09/12
3 R-matrix calculations S(300)
E10
E20
Casc.
Total
Fey et al
(2004)
2 experiments + previous
Ecm eff: MeV
77  17 keVb
81  22 keVb
4  4 keVb
162  39 keVb
Buchmann and Barnes
(2006)
All available data
+ ERNA +DRAGON
80  20 keVb
53+13 keVb
7+13 keVb (6.92 MeV)
25+16 keVb (6.05 MeV)
-18 -4
-15
(S=165 keVb)
NACRE
(1999)
79  21 keVb
120  60 keVb

17. Future : Dense jet gas vs 12C targets
16N → b- + 16O → a + 12C
New measurements to increase the precision on the SE1
Recoil separators :
2 in use : DRAGON (TRIUMF) and ERNA (Bochum)
Detection efficiency : up to 100% of the more probable charge state at the charge equilibrium (50% of the 16O with a poststripper)
- present limitations : intensity through WF, target extension
only the total cross section
R&D
Future : Dense jet gas vs 12C targets
(Coincidences with) a new g-ray detector array
(angular distributions, cascades)
R&D
A. Lefebvre-Schuhl
FINUSTAR /09/12

18. Future : Accelerator of intense 4He beam
Such as a 3 to 5 MV Pelletron with ECR source
With pulsed beams?
+ a recoil separator
(for inverse kinematics studies)
with dense jet gas target
(R&D needed to reach low energies)

19. + a new g-ray detector array
energy resolution vs efficiency
enough statistics
to separate the transitions
With Ge detectors ?
10.76
7.93
6.02
4.74
4.61
4.50 K
1.78
27Al (p,g) 28Si
Ep = 992 keV
LaBr3(Ce) 2’’x2’’
Preliminary results : Cimala et al.
Kraków, Debrecen, Orsay, Warsaw
or new ones ?
Preliminary results : Cimala et al.
Kraków, Debrecen, Orsay Warsaw
A Paris detector ?
(LaBr3 + CsI)

20. Eurogam-detector collaboration
M. Assunção, M. Fey, A. Lefebvre-Schuhl, J. Kiener, V. Tatischeff, J.W. Hammer, C. Beck, C. Boukari-Pelissie, A. Coc, J.J. Correia, S. Courtin, F. Fleurot, E. Galanopoulos, C. Grama, F. Haas, F. Hammache, F. Hannachi, S. Harissopulos, A. Korichi, R. Kunz, D. Ledu, A. Lopez-Martens, D. Malcherek, R. Meunier, Th. Paradellis, M. Rousseau, N. Rowley, G. Staudt, S. Szilner, J.P. Thibaud, J.L. Weil
CSNSM-Orsay; IfS-Stuttgart; IPHC/IReS-Strasbourg; KVI-Groningen;
INP-Athens; GSI-Darmstadt (IPN-Orsay); PI-Tübingen; DP-Lexington (II-Budapest)
ERNA’s collaboration
L. Gialanella, G. Imbriani, A. Ordine, V. Roca, M. Romano, R. Kunz, A. di Leva, D. Rogalla, C. Rolfs, D. Schürmann, F. Strieder, N. De Cesare, A. D'Onofrio, C. Lubritto, F. Terrasi, A. Lefebvre-Schuhl, J.P. Thibaud, C. Beck, S. Courtin, F. Haas, D. Lebhertz, M.-D. Salsac, F. Hammache, N de Séréville, F. de Oliveira; P. Papka, S. Harissopulos, A. Lagoyannis, Th. Konstantinopoulos
INFN & Univ.-Naples; IE3-Bochum; CSNSM-Orsay; IPHC-Strasbourg;
IPN-Orsay; GANIL-CAEN; iTLABS; INP-Demokritos
PARIS collaboration
100 physicists, engineers and PhD students, 38 institutions from 16 countries and principally : IFJ PAN-Kraków, ATOMKI-Debrecen, CSNSN-Orsay and Univ.-Warsaw

21. LaBr3(Ce) 2’’x2’’
NaI 4’’x4’’
10.7  0.

23. To separate cascades through 7.12, 6.92, 6.05 ?
g-ray width for a 2''x2'' at 15 cm
Ecm (MeV)
3,00
2,00
Eg at rest (MeV) 10 7 3 9 2
Eg at rest x 0,02 (keV)
203
140 63
183 43
Doppler shift at 90° (keV)
117 81 34 86 66 18
In inverse kinematics,
Doppler shift : not too constraining !