1. Indirect reactions for astrophysics @ the Tandem-Alto Pole of Orsay
Faïrouz Hammache
(IPN-Orsay, France)
LEA-workshop
Catania, October 2008

2. Nuclear astrophysics using indirect reactions @ Tandem-Orsay (end 2005-2008)
Collaboration
Aim of the experiments
Indirect Method
IPN-CSNSM-ULB-GANIL-GSI
13C(a,n)16O
Neutron source in AGB stars (1-3 M)
13C(7Li,t)17O -transfer reaction
PRC77 (2008)
IPN-LT(BEJAIA)-CSNSM-ULB-GANIL-GSI
12C(a,g)16O
He-burning in massive stars
12C(7Li,t)16O -transfer reaction
Analysis in progress
IPN-CSNSM-LNS-GANIL-SUBATECH
25Al(p,g)26Si
26Al synthesis in Novae
24Mg(3He,n)26Si*
Analysis in progress

3. Study of 13C(a,n)16O reaction via 13C(7Li,t)17O transfer reaction
IPNO-CSNSM-ULB-GANIL-GSI
 s-process nucleosynthesis (n,) half of the heavy elements in Univers
 90<A<209  low-mass
AGB stars 1-3 M (Temperatures108K)
Hydrogen shell
He shell CO
core
12C(p,)13N(+)13C
Convective
envelope
13C pocket
13C(,n)16O
He intershell
Neutron source 13C(,n)16O
dYn/dt =Y13C.Y4He..NA<>13C(,n)-YX.Yn..NA<>X(n,)

4. Status of 13C(a,n)16O reaction
Gamow peak ~190 keV100 pb
S-factor S(E)=E(E)exp(2)
S(E)=E(E)exp(2)
Ecm
 Drotleff et al.
(Sa=0.7)A (Sa=0.0)B
7.166
6.862
? S? 
6.359 ½+
13C+ ½- n
/2-
Ecm (keV)
4.143
/2-
16O+n
S= (theoretical values)
Enough neutrons  s-process nucleosynthesis
17O
 Kubono et al.  13C(6Li,d)17O(DWBA) S(exp)0.011!!!
 Keeley et al. reanalysis of Kubono data  S(exp)=0.4
factor 40 ?!?!?!

5. Study of 17O states by 13C(7Li,t)17O -transfer reaction
SPLIT-POLE spectrometer (Orsay-Tandem) E
tritons
13C(7Li,t)17O t
13C target 80 g/cm2
pos
34,28MeV
Position gas chamber (B)
Faraday Cup
E proportional counter
E-E
monitor
 E7Li = 28 MeV
 Transfer measurements on 13C and 12C targets[0°-32°]
 13C(7Li,7Li)13C measurements
 E7Li = 34 MeV
Transfer measurements on 13C and 12C targets [0°-32°]
 13C(7Li,7Li)13C 34 MeV from Schumacher et al. NPA 212 (1973) 573

6. Comparison between our data and FRESCO calculations  S
assume :Sa=1 for 7Li
For MeV
Sa=0.260.06
Furutani et al. (S=0.25)
no need to add
compound nucleus
component
Clark et al.
S=0.25
S=0.35
S=0.290.11
in agreement with Kelley’s value
6.356 (1/2+)
6.356 (1/2+)

7. 13C(,n)16O Astrophysical S-factor
190 keV 
1.4 MeV-b
(S1/2+ is about 70% of the total) 
The contribution of the
6.356 (1/2+) subthreshold state
is dominant at
astrophysical energies
Orsay
3/2+ (843 keV)
Drotleff 93
 Brune 93
Gamow peak
M.G. Pellegriti, F. Hammache et al. PRC 70 (2008)
Orsay range of allowed values for <v> is substancially reduced in comparison to Nacre compilation

8. 12C(a,g)16O the Holy Grail of Nuclear Astrophysics
IPNO-LT(BEJAIA)-CSNSM-ULB-GANIL-GSI
12C(a,g)16O in stellar helium burning
@ T=0.2 GK
Main reactions: 312C & 12C(a,g)16O
12C/16O abundance ratio
nucleosynthesis & subsequent
stellar evolution of massive stars
BUT: E0=300 keV, (E0) ~ 10-8 nb
2? Sa
2?Sa
s(E0) is expected to be dominated by
E1 & E2 transitions.

9. Sa values for 6.05, 6.13, 6.92 & 7.12 MeV states of 16O
J(Ex, MeV)
6Li
48 MeV
(1998)
6Li
42 MeV
(1978)
6Li
90 MeV
(1980)
7Li
34 MeV
(1978)
0+ (6.05)
0.120.05
0.81
3.58
0.12 0.04
3- (6.13)
0.290.15
1.08
0.52
0.09 0.04
2+ (6.92)
0.37 0.11
1.35
0.82
0.18 0.05
1- (7.12)
0.160.05
1.08
0.86
0.07 0.05
Experimental problems ?
Analysis procedure ?
optical potential parameters ?
overlap of interaction mechanism, multi-step effects?

10. FRDWBA calculation still in progress
Study of 6.92 & 7.12 MeV 16O states by 12C(7Li,t)16O -transfer Tandem-Orsay
12C(7Li,t)16O measured spectrum
@ 9 degree
FRDWBA calculation still in progress
Very preliminary d/dcm
Thesis of N. Oulebsir (Béjaïa University)

11. 26Al nucleosynthesis in Novae IPNO-CSNSM-LNS-GANIL-SUBATECH
COMPTEL Map of Galaxy @
1.809 MeV g-ray
Stellar sources of 26Al:
 Massive stars (SNII, Wolf Rayet)
AGB stars
Novae
25Al(p,g)26Si competes with
25Al(b+) 25Mg (t1/2 = s )
25Al(p,g)26Si reaction rate
has large uncertainties 
26Al yield abundance is unknown
Two sequences to produce 26Al (T1/2= yr):
26Si
25Al
26Al m
1.809 MeV
Spectroscopy of 26Si* via
24Mg(3He,n)26Si* reaction
g.s
24Mg
25Mg
26Mg

12. 24Mg(3He,n)26Si*(g)26Si measurement
ONLINE
Set-up:
Pulsed 3He 7.9 MeV
I=60 pnA
Target: 150 g/cm2 of 24Mg
Measured g-spectrum
511 keV
4th Ex  1st Ex
972 keV
1st Ex of 26Si
@ 1795 keV
4 Ge detectors
Analysis in progress
E (keV)
ToF spectrum (n-g coin)
g prompt
region
of interest
36 EDEN detectors
ToF (au)

13. Futur projects: AGB stars @ Tandem-Orsay
 22Ne(a,n)25Mg : neutron source in AGB stars of intermediate mass
 2a of low-energy resonances, J of subthreshold resonances
 22Ne(7Li,t)26Mg @ Split-Pole
 14C(a,g)18O & 19F(a,p)22Ne: 19F nuclesynthesis
2a of low-energy resonances
 Transfer reactions using MUST2 detectors or Split-Pole

14. Spectroscopy of 26Si via 24Mg(3He,n)26Si*
Study of 13C(a,n)16O & 12C(a,g)16O reactions via (7Li,t) -transfer reactions
F.Hammache, M. G. Pellegriti*, P. Roussel, L. Audouin, D. Beaumel, S. Fortier (IPN-Orsay) N. Oulebsir (LT-Béjaïa)
sss
J. Kiener, A. Lefebvre-Schuhl, V. Tatischeff (CSNSM-Orsay)
P. Descouvemont (ULB-Brussels)
L. Gaudefroy (GANIL-Caen)
M. Stanoiu (GSI-Darmstadt)
* LNS-Catania
Spectroscopy of 26Si via 24Mg(3He,n)26Si*
sssN. De Séréville, F.Hammache, S. Giron, S. Fortier, P. Roussel, M Baptiste, D. Beaumel, M.
Chabot, M. Ferraton, S. Franchoo, F. Maréchal, C. Petrache, J.A. Scarpaci,
I. Stefan, D. Verney (IPN-Orsay)
A. Coc, J. Duprat, C. Hamadache, J. Kiener, A. Lefebvre-Schuhl (CSNSM-Orsay)
J.C. Dalouzy, F. Grancy, F. De Oliveira, J.C. Thomas (GANIL)
L. Lamia, G. Pizzone, S. Romano (LNS-Catania)
M. Fallot, L. Giot (SUBATECH)