Underground Measurement of the 17O+p Reactions
Carpathian SSP12
David Scott
On behalf of the LUNA collaboration
• Astrophysical Motivation
• The 17O(p,γ)18F Reaction:
- Current Status
- Present Investigation
• Future direction: The 17O(p,α)14N Reaction
Astrophysical Motivation
•
Site: Classical Novae
(Cygni 1992)
•
•
Significant source of 17O, 15N and 13C
Reactions: 17O(p,γ)18F and 17O(p,α)14N
14N
(p,α)
17O
(p,γ)
18F
(β+ν)
I
II
CNO Cycle
III
18O
•
•
Annihilation 511 keV gamma-rays following β+ decay of 18F (t1/2=110 mins)
Potential constraints on current novae models
The 17O(p,γ)18F Reaction in Novae
• Classical novae T=0.1-0.4 GK => EGamow = 100 – 260 keV
• Resonant Contribution: 17O(p,γ)18F resonance at Ep = 193 keV
Ex(keV)
Ep= 193keV
Gamow
Peak
5789
17O+p
1080
937
18F
• Also Non-resonant Contribution
Previous Investigations (S-factor)
LUNA
•
•
•
•
•
1st investigation of the 17O(p,γ)18F reaction [Rolfs et al. Nuc. Phys. A217 29-70 (1973)]
S-factor calculated , 1st meas. of 193 keV resonance [Fox et al. Phys. Rev. C 71, 055801 (2005)]
Activation measurement [Chafa et al. Phys. Rev. C 75, 033810 (2007)]
Ecm = 257 – 470 keV measurement [Newton et al. Phys. Rev. C 81, 045801 (2010)]
Inverse kinematics at DRAGON [Hager et al. Phys. Rev. C 85, 035803 (2012)]
Previous Investigations (Resonance)
Ex(keV)
Ep= 193keV
5789
17O+p
1080
937
18F
ωγ193= (1.2±0.2)×10-6 eV [Fox et al. Phys. Rev. C 71, 055801 (2005)]
ωγ193= (2.2±0.4)×10-6 eV [Chafa et al. Phys. Rev. C 75, 033810 (2007)]
Clear discrepancy between measurements
Aims of Our Investigation
To Measure:
• The total S-factor for the 17O(p,γ)18F reaction in the energy
range important for Classical Novae.
• The strength of the Ep=193 keV resonance.
Measurements made using both prompt-gamma and
activation techniques.
The LUNA Accelerator at Gran Sasso
~1400
m
Experimental setup
•
•
400 kV electrostatic accelerator
Up to 400 keV protons with a maximum current ~400 μA
•
•
70% Enriched 17O targets on tantalum backings (prepared via anodization process)
~5cm of lead shielding surrounding detector
Oxygen Enriched Targets
Strong 18O resonance used to monitor target degradation
Ex(keV)
Ep = 151 keV
8137
Fresh Target
23C
10C
18O+p
Eγ=4.2 MeV
3908
38C
19F
also studied with
SIMS and RBS
measurements.
On and Off Resonance Spectra
Off-Resonance
On-Resonance
On-Resonance
Off-Resonance
New Transitions Observed
Ex(keV)
5789
Ep= 193 keV
Black = Previously Observed
Blue = First Observation
17O+p
3839
3791
3358
3134
2523
2101
1080
1041
937
18F
Coincidence Summing
2
3
Intensity
1
1
3
Including
summing
effects
No summing
effects
2
Energy
•
•
Summing-in for 3 ∝ B1B2ε1ε2
summing-out for 1 ∝ B1B2ε1εT2
Simple decay cascade => summing effects generally small
Results
• Total reaction cross section measured between Ecm ≈ 200 – 370
keV measured leading to a five-fold reduction in reaction rate
uncertainty.
• Resonance Strength of Ep=193 keV resonance measured within an
uncertainty of 8%. (~factor 2 higher accuracy).
Results from activation and prompt-gamma measurements in good
agreement.
Analysis complete. Paper in preparation for publication.
The 17O(p,α)14N Reaction
14N
(p,γ)
(p,α)
17O
18F
(β+ν)
I
II
III
18O
17O(p,α)14N
reaction in competition with 17O(p,γ)18F
The 17O(p,α)14N Reaction
Previous Investigations:
Ep = 193 keV resonance strength: Three independent measurements in fairly good
agreement (1.6±0.2) x10-3 eV [Chafa et al PRC 75 (2007) 035810-1 – 15]
(1.7±0.15 x10-3 eV [Moazen et al PRC 75 (2007) 065801-1 – 7]
(1.66±0.17) x10-3 eV [Newton et al PRC 75 (2007) 055808-1 – 4]
Ep = 70 keV resonance strength:
Berheide et al ZPhys A 343 (1992) 483-487
Blackmon PRL 74 (1995) 2642-2645
Sergi et al PRC 82 (2010) 032801(R)
Experimental Setup
Target
Beam
Outer Al Dome
Inner Cu Dome
8 Silicon Detectors, approximately 0.6π coverage (~15% efficiency)
Approximately 2 counts/hour expected for 70 keV resonance.
(assuming 100 μA beam current and 95% 17O enriched targets)
First Spectra Acquired
18O
Resonance Scan
~2.8
18O(p,α)15N
MeV α
Detector Calibration
The Luna Collaboration
A. Formicola, M. Junker Laboratori Nazionali del Gran Sasso, INFN, ASSERGI
M. Anders, D. Bemmerer, Z. Elekes Forschungszentrum Dresden-Rossendorf, Germany
C. Salvo INFN Genova & INFN Napoli, italy
Di Leva INFN, Napoli, Italy
C. Broggini, A. Caciolli, R. Depalo, R.Menegazzo, C. Rossi Alvarez INFN, Padova, Italy
C. Gustavino INFN, Roma La Sapienza, Italy
Zs. Fülöp, Gy. Gyurky, T. Szucs, E. Somorja Institute of Nuclear Research (ATOMKI), Debrecen, Hungary
O. Straniero Osservatorio Astronomico di Collurania, Teramo, and INFN, Napoli Italy
C. Rolfs, F. Strieder, H. P. Trautvetter Ruhr-Universität Bochum, Bochum, Germany
F. Terrasi Seconda Università di Napoli, Caserta, and INFN, Napoli, Italy
M. Aliotta, T. Davinson, D. A. Scott The University of Edinburgh, UK
P. Corvisiero, P. Prati Università di Genova and INFN, Genova, Italy
A. Guglielmetti, M. Campeggio, D. Trezzi, C. Bruno Università di Milano and INFN, Milano, Italy
G. Imbriani, V. Roca Università di Napoli ''Federico II'', and INFN, Napoli, Italy
G. Gervino Università di Torino and INFN, Torino, Italy