• Context of the experiments

• Our previous experiments performed at Triumf :Our previous experiments performed at Triumf :

➢ 1212C(C(1212C, )γC, )γ 2424Mg experiment : @ EMg experiment : @ Ecmcm

=6-8 MeV =6-8 MeV

➢ 1212C(C(1616O, )γO, )γ 2828Si experiment : @ ESi experiment : @ Ecmcm

=8.5-9 MeV =8.5-9 MeV ➢

• The actual The actual 1212C(C(1616O, )γO, )γ 2828Si experiment (#1219) :Si experiment (#1219) :

➢ Goal of the experiment Goal of the experiment ➢ On line spectraOn line spectra

The 12C(16O,)28Si Radiative Capture : Structural and Statistical Aspects of the

-Decay

Resonant Structures

Molecular states ?

Molecules and deformation : search for signatures in the decay specificity of the gamma decay of resonant structures

Campaign of radiative capture experiments in the 12C+12C and 12C+16O systems

E. C. Schloemer et al., Phys. Rev. Lett. 51 (1983), 881.

E. Almqvist et al., Phys. rev. Lett. 4 (1960), 515.

12C+12C and 12C+16O systems show narrow resonances at CB correlated in different reaction channels

• 12C+12C cluster breakup states in 24Mg up to EX = 50 MeV C.J. Metelko et al., Phys.Rev. C68 (2003) 0544321

•12C+16O cluster breakup states in 28Si up to EX = 45 MeV C.J. Metelko et al., J. Phys. G29 (2003), 697

• Reactions 12C(16O,12C12C) and 12C(20Ne,12C16O)

BC

28Si breakup states into 12C+16O / 24Mg breakup states into 12C+12C

Starting point

28Si(12C-160) Ohkubo and Yamashita, Phys.Lett. B 578 (2004) 304. 24Mg(12C-12C) P. Descouvemont and D. Baye,

Phys.Lett. 169 B (1986) 143.

Links between low-lying members of these cluster bands ?

•Theoretical point of view (AMD, GCM, cluster models,ACM …)

Structure of these states?

12C(12C,γ)24Mg

A.M. Sandorfi, in Treatise on Heavy-Ion Science, D.A. Bromley, Vol II, sec. 3.

To the ground state

To the first 2+

To the 4+ and 2nd 2+

12C(16O,γ)28Si

To the ground state

To the first 2+

Radiative capture

Experimental study : 12C+12C -> 24Mg + /γ 12C+16O -> 28Si + γSandorfi et al. (Brookhaven) : Large NaI(Tl) (~ 1980) Eγ > 18 MeV.

Deexcitation of the RC resonances to the low-lying states of 24Mg and 28Si

19.3 MeV

16.76 MeV

A signature for molecular configuration : characteristic gamma decay of resonant structure ?

Radiative Capture

Fusion-Evaporation

17.18 MeV

∼ 25.5 MeV

γ

0 MeV

12C+ 16O

28Si

ααn

p

α11.7 MeV

9.98 MeV

20Ne27Si

27Al24Mg

γ

γ

BC∼7.8 MeV

NRC/NFE≈1.5 ×10-5

Selection of RC recoils around 0° NRC/NBeam≈6.5 × 10-12

Search of molecular signature

D.A. Hutcheon et al., NIM A 498, 190 (2003).

first stagefirst stage

ISAC I : Stable beams (OLIS):16O 0° spectrometer (Acceptance : cone ½ angle 25 mrad) Beam rejection 10Beam rejection 101313

Tof on 21 m Focal plan Si detector (DSSSD) BGO array (ε = 50% at 5 MeV)

Dragon features

1-1.3 MeV/uELab

12C (40 g/cmμ 2)Target

10-20 pnAIntensity

16O , 12CBeam

12C(16O, )γ 28SiReaction

22ndnd stage stage

Experimental Details

D.A. Hutcheon et al., NIM A 498, 190 (2003).

first stagefirst stage

1-1.3 MeV/uELab

12C (40 g/cmμ 2)Target

10-20 pnAIntensity

16O , 12CBeam

12C(16O, )γ 28SiReaction

22ndnd stage stage

Experimental Details

TOF

D.A. Hutcheon et al., NIM A 498, 190 (2003).

first stagefirst stage

1-1.3 MeV/uELab

12C (40 g/cmμ 2)Target

10-20 pnAIntensity

16O , 12CBeam

12C(16O, )γ 28SiReaction

22ndnd stage stage

Experimental Details

TOF

D.A. Hutcheon et al., NIM A 498, 190 (2003).

first stagefirst stage

1-1.3 MeV/uELab

12C (40 g/cmμ 2)Target

10-20 pnAIntensity

16O , 12CBeam

12C(16O, )γ 28SiReaction

22ndnd stage stage

Experimental Details

TOF

E*(24Mg, 28Si) ~ 20 and 25 MeV intermediate states

involved in the decay

Doorway states located above the α emission threshold

~ 14 MeV

2+ 0+

3- 0+

4+ 2+

12C(16O,γ)28Si, ECM = 8.5 MeV

E0(MeV)

12C(12C,γ)24Mg, ECM = 6.8 MeV

~ 10 MeV

E0(MeV)

D.G. Jenkins et al. Phys. Rev. C71 (2005) 041301(R).D.G. Jenkins et al. Phys. Rev. C76 (2007) 044310.S. Courtin et al., AIP Conf. Proc. 853 (2006) 134., Fusion’06, Venice.S. Courtin et al., J. Phys. 111 (2008) 012005, CLUSTER’07, Stratford-upon-Avon.D. Lebhertz et al., Int. J. Mod. Phys. E17, (2008), 2044.P. Marley (York), D. Lebhertz (Strasbourg) PhD Thesis, in preparation.

Results

E0(MeV)

E1(M

eV

)At all 3 energies: 3- state strongly fed directly … (p-h excitation)At ECM = 9 MeV: direct feeding of the 43

+ (prolate)

3-0+

7.4 MeV

16 MeV gated

E0(MeV)

E0(MeV)

E0(MeV)

E1(M

eV

)

S. Courtin et al., AIP Conf. Proc. Fusion’08, Chicago.D. Lebhertz (Strasbourg) PhD Thesis.

ECM = 8.5 MeV

ECM = 9 MeV

Results of the previous Dragon 12C+16O experiment

simulation

experiment

E0(MeV)

α

p

nαα

24Mg

28Si

20Ne

10 MeV

g.s.

25 MeV

Very well known sd shell nucleusBound and quasi-bound states

Jπ = 5--6+

E0(MeV)

Complexity of Dragon’s acceptance numerical simulations (GEANT)→28Si fully tracked down through Dragon

Results : Monte-Carlo simulations vs data, 12C+16O

Summary

system6

6.4 BG6.87.58

8.58.89

Ecm

(MeV) J previous cr

our cr

12C+12C (0+)-2+ 0.8 b 1.6 b12C+12C 0.4 b 0.8 b12C+12C (0+)-2+ 1.5 b 3.1 b12C+12C 2+-4+ 0.9 b 2.0 b12C+12C (2+)-4+ 1 b 2.4 b

12C+16O 5--6+ 2.3 b 11.6 b12C+16O 5--6+ 2 b 16.3 b12C+16O 6+ 3.1 b 23.4 b

Previous->New Experiment

CC calculations by N. Rowley

CB 7.8 MeV

This exp.

A.M. Sandorfi, in Treatise on Heavy-Ion Science, D.A. Bromley, Vol II, sec. 3.

P.R. Christensen, Z.E. Switkovski and R.A. Dayras, Nucl. Phys. A280 (1977) 189.

ECM=6.6 MeV

ECM=7.2 MeV

Choice of the bombarding energy

Jπ

3-

2+

1-

0+

E0(MeV)

E0(MeV)

E0(MeV)

Yie

ldYie

ldYie

ldYie

ld

E0(MeV)

Counts

E0(MeV)

Cou

nts

E0(MeV)

Coun

ts

E0(MeV)

Coun

ts

E0(MeV)

Spin assignment for the resonance

SimulationsEcm = 7.2 MeV

Enhanced feeding of the prolate 0+ from Jπ = 2+SimulationsECM = 7.2 MeV

enhanced feedingstatistical

Structural effects

Highly enriched, 50 µg.cm-2 12C target

Dragon / BGO array / Solid target holderq( 16O) = 3+ <- SnG sourceq(28Si) = 8+ (30%)

16O beam :-> Up to this morning : E

lab= 17.05 MeV

120 enA / Dead Time ≈ 20 %-> Now E

lab= 15.65 MeV / 200 enA

σ fus (m

b)

Ecm (MeV)

CB

Previous exp.

This exp.

Experimental details

Ecm

(MeV)

8.5

7.8

7.26.9

6.6

On line results

TOF

DSSSD

E0 > 6 MeV

0.511 MeV1.8 MeV

1.8 MeV

10-14 MeV23 MeV

BGO

E0(channel)

E1(c

hannel)

On line results

● S. Courtin, A. Goasduff, F. Haas, D. Lebhertz (IPHC Strasbourg, France)

● D.G. Jenkins (University of York, UK)

● C. Ruiz, D. Hutcheon, J. Fallis, U. Hager, C. Davis, D. Ottewell, G. Ruprecht, P.-A Amandruz

(TRIUMF, Dragon's group)

Collaborators