EuroGENESIS workshop
Reactions of Astrophysical Interest
Madrid Apr 2011
Carbon - Carbon Burning and Other
Research Topics of Zagreb IP
Zagreb IP: Experimental nuclear physics inputs
for thermonuclear runaway - NuPITheR
Neven Soić, Ruđer Bošković Institute, Zagreb, Croatia
Objective
• use of our expertise from structure and reaction studies to study nuclear
reactions important for stellar explosive phenomena: novae, SnIa , X-ray bursts
and super-bursts
• not direct low energy measurements of the reactions, focus on reactions which
in astrophysically relevant energy range are likely to proceed through
resonances which dramatically increase cross section of the reaction
• our main goal and objective is to obtain new results on the properties of these
resonances and their full characterization
• full characterization of the resonances => obtained data will be important
ingredients for calculations of improved reaction rates
• these indirect measurements complement direct measurements and provide
useful input for setup of future direct experiments
Carbon – carbon burning
• Objective: search for 12C+12C resonances at 24Mg excitations 14.5 20 MeV and full characterization of the resonances (excitation
energy, width, spin, parity, partial decay widths)
• Two-fold reason: nuclear structure & astrophysical motivation
D. A. Bromley,
J. A. Kuehner,
E. Almquist, Phys.
Rev Lett 4 (1960) 385
Elastic scattering
data
Resonant phenomena
in heavy ion reaction
E. Almquist, D. A.
Bromley, J. A. Kuehner,
Phys Rev Lett 4 (1960)
515
Reaction data
Formation of quasimolecular states in
24Mg
50 years later:
- number of resonances decaying into various channels
- kind of unique nuclear system, very complex structure
- governed by cluster structure of 12C – oblate deformation in gs
- not fully understand yet
B. R. Fulton et al, Phys
Lett B 267 (1991) 325
M. Freer et al, Phys Rev C
57 (1998) 1277
C. Metelko et al, Phys Rev C
68 (2003) 054321
M. Freer et al, Phys Rev C 57 (1998) 1277
But main focus of these studies
has been on higher excitations
in 24Mg
No data below 20 MeV !
• Low energy data for 12C+12C fusion reaction crucial for many
astrophysical phenomena: quiescent burning of massive starts,
super-AGB stars, super-bursts and supernovae type Ia
• The most relevant quantity: total reaction fusion rate
12C + 12C → 24Mg + 
12C + 12C → 20Ne + α
Existing data show large discrepancies
12C + 12C → 23Na + p
Low energy resonance ?
12C + 12C → 23Mg + n
E. F. Aguilera et al, Phys. Rev. C 73 (2006) 064601
T. Spillane et al, Phys. Rev. Lett. 98 (2007) 122501
Stellar outbursts
12C+12C
fusion is differentiating
between the evolutionary paths
leading to either white dwarf or
heavy elements burning stages
Bull’s eye
Explosive phenomena in
binary systems
SNIa: initiates thermonuclear
runaway on white dwarf
temperature range is
0.5 - 1.2x109 K
Ecm=1.5-3.3 MeV
Super-bursts: trigger of
12C ignition
9 K - 5.7 MeV
up
to
2.5x10
most powerful events since the Big Bang
Gamma Ray Bursts
(energy released in few seconds larger
than Sun’s output over its entire lifetime)
12C+16O
measurement at LNS Catania
Coincident detection of 2 reaction products
12C + 16O → 4He + 12C + 12C
Q=-7.16 MeV Ethr(24Mg)=13.93 MeV
→ 4He + 16O + 8Be
Q=-7.37 MeV Ethr(24Mg)= 14.14 MeV
→ 4He + 20Ne + 4He Q=-2.54 MeV Ethr(24Mg)= 9.31 MeV
→ 4He + 23Na + 1H
Q=-4.92 MeV Ethr(24Mg)= 11.69 MeV
16
Excitation energy range: 0.5 – 6 MeV
above the 12C + 12C threshold, 14.5 –
20 MeV in 24Mg excitation

O
24
12
C
Mg
Resonance parameters:
excitation energy, width,
spin, parity and
partial decay widths of the resonances
Kinematics of the reaction A(a,bc)B
Q = E1L + E2L + E3L - E0L
EbL mb  mB   EcL mc  mB   2 ma mb EaL EbL cos bL 
2 ma mc E E cos  2 mb mc E E cos
L
a
L
c
L
c
L
b
L
c
L
b c

ma 
L

 mB Q  Ea 1 
 mB  

EiCM  EiL  2ai EiL cos iL  ai2
CM
Ec  B  Etot

CM
tot
E
mi ma EaL
miV 2
ai 

2
ma  m A
mb  mc  mB CM
Eb
mc  mB
mA
Q
EaL
ma  mA
Eb c
L L
EL EL

E
L
b
c
b Ec
 b c 

2
cosb c 
mb mc
 mb mc


cosbLc  cosbL coscL  sin bL sin cL cos bL  cL

Spin/parity = angular correlations
M. Freer, Nucl Instr Meth Phys Res A 383 (1996) 463
All involved particles in the reaction 0+
model independent
around Θ*=0
Main goal: identify low spin states with
significant 12C+12C partial width
Experimental setup
•
16O
beam energies: 90 MeV, target: 60 μm/cm2 carbon target
Detector telescopes: 50 x 50 mm2
20 μm SD + 1000/500 μm PSD
Particle identification from p to 12C
Test simulations:
Energy resolution 40 - 100 keV
Q-value 500 keV
Excitation energy resolution
(24Mg excitations 0.5 - 6 MeV)
50 to 160 keV.
Excitation energy error <50 keV
Direct measurement of 20Ne(α,12C)12C reaction
•
•
•
•
•
•
•
•
•
•
resonant reaction measurement
possible experimental sites: LNS Catania, Argonne National Lab
4He gas target – scattering chamber filled up with gas at low pressure
20Ne beam of 60 – 100 MeV
Q = - 4.62 MeV
beam slows down through gas, at resonance energy enhanced
production of 12C+12C – coincidence detection
reaction products identical => particle identification using reaction
kinematics
measurements of angular distributions – resonance characterization
pure beam and target => low background
very challenging experiment
Direct measurement of 23Na(p,12C)12C reaction
• resonant reaction measurement
• possible experimental site: LNS Catania if sodium beam from
tandem will be developed
• beam energy 70 – 130 MeV
• scanning for resonances
• target: thick CH2
• coincidence detection, angular distributions
• Q = - 2.24 MeV
• possible background from carbon component of the target
• low energy of reaction products – particle identification
problem
Expected results
In summary, expected results of the measurements will provide
answers to following questions:
How many resonances are at 24Mg excitations 14.5 – 20 MeV ?
Do exist 12C+12C resonance at low excitations 14.5 – 16 MeV ?
If yes, what are resonance parameters ?
Is there any low spin resonance which may influence carboncarbon burning ?
5) How much observed resonance affects carbon-carbon burning ?
6) Do observed resonances help in explaining 24Mg structure ?
1)
2)
3)
4)
Resonances in 18Ne
• important for reaction rates of the 14O(α,p)17F and 17F(p,)18Ne
reactions at relevant energies in stellar explosions
• the 1st of these reactions is important in hot CNO cycle, largely
influences energy production in X-ray bursts thermonuclear
runaway affecting later nucleosynthesis
• the 2nd reaction is of importance for novae nucleosynthesis,
escape from HCNO
• objective: study of 18Ne resonances in relevant excitation energy
range (4.0-6.5 MeV) by studying decays of 18Ne* into 14O+α and
17F+p
• measurement of the breakup of radioactive 18Ne beam on 12C
target into 14O+α and 17F+p – SPIRAL GANIL
LEVEL SCHEME OF 18Ne
Information on 14O(,p)17F reaction rate from:
T9 ~ 1.5
 level structure of 18Ne
T9 ~ 1.0
 theoretical calculations
 inverse reaction 17F(p,)14O
 some direct data
5.114
14O
T9 ~ 0.1
+
3.922
17F + p
main, expected contributions to reaction rate from:
resonance at 6.15 MeV J = 1-
@ T  1.0x109 K
direct contribution with l =1
states at ~ 7 MeV
@ T  1.5x109 K
Other possible reactions for study of 18Ne* into 14O+α and 17F+p
Stable beam experiments, available some inclusive experimental
data
Proposed coincident measurements
1)
2)
3)
16O(3He,n)18Ne*
14N(10B,6He)18Ne*
20Ne(p,t)18Ne*
The 18F(p,)15O reaction
• Experiment approved at ORNL USA – spokesperson I. Martel
Huelva, co-spokesperson N. S. RBI, Zagreb
• Goal: the energy, widths and spins of the relevant states in 19Ne in a
range of excitation energies between 7 - 8 MeV; a detailed
determination of the spectroscopic properties of these levels, as
well as to investigate the impact in the astrophysical reaction rates
• Measurement of the 18F(p,)15O reaction rate in a range of energies
between 0.6 - 1.8 MeV (CM)
• Measurement of the level energy, width and spin for the resonances
in the region around 1089 keV, 1225 keV, 1347 keV and 1573 keV
• Detailed exploration the energy range between 750 keV and 1100
keV searching for possible resonances.
• We will as well obtain information on the 18F(p,p)15O reaction which
will complement information on 19Ne resonances.
• Beam
• 18F beam at 80 MeV. It should be fully stripped to 9+ to reduce 18O
contamination at the analysis magnet. Estimated intensity is 106 pps.
• Targets
• A foil of large Z value (eg. Au 9um) will be placed at the entrance of the
reaction chamber to reduce energy of the beam down to 40 MeV.
Coulomb barrier for Au+F is estimated around 97 MeV, so we would
expect small contribution from additional nuclear reactions.
• A thick target of polyethylene (CH2)n of 35um (reaction target). This
thickness is sufficient to stop a beam of 18F at 40 MeV Lab (2.0 MeV at
CM). The target will be metalized on the back by a thin gold layer (few
ug/cm2), so that data can be normalized using 18F + 197Au elastic scattering
at backward angles. Elastic scattering will also serve as monitor of possible
beam contamination.
• A thin carbon foil will be used during 1 shift for controlling reactions on
the C ions of the target and other possible source of background.
Summary and Conclusion
• Main focus on carbon – carbon burning
• Experiment on 18Ne resonances will be
proposed at GANIL before the project end
• We are open for collaboration and look
forward for common experiments with other
IPs