1. 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

2. Astrophysical Motivation
Site: Classical Novae
Significant source of 17O, 15N and 13C
Reactions: 17O(p,γ)18F and 17O(p,α)14N
Annihilation 511 keV gamma-rays following β+ decay of 18F (t1/2=110 mins)
Potential constraints on current novae models
(Cygni 1992)
(p,γ)
(β+ν)
(p,α)
17O
18F
14N
13C
13N
12C
15N
16O
18O
15O
17F
CNO Cycle I II
III

3. The 17O(p,γ)18F Reaction in Novae
Classical novae T= GK => EGamow = 100 – 260 keV
Resonant Contribution: 17O(p,γ)18F resonance at Ep = 193 keV
Also Non-resonant Contribution
Ex(keV)
Gamow
5789
Ep= 193keV
Peak
17O+p
1080
937
18F

4. Previous Investigations (S-factor)
LUNA
1st investigation of the 17O(p,γ)18F reaction [Rolfs et al. Nuc. Phys. A (1973)]
S-factor calculated , 1st meas. of 193 keV resonance [Fox et al. Phys. Rev. C 71, (2005)]
Activation measurement [Chafa et al. Phys. Rev. C 75, (2007)]
Ecm = 257 – 470 keV measurement [Newton et al. Phys. Rev. C 81, (2010)]
Inverse kinematics at DRAGON [Hager et al. Phys. Rev. C 85, (2012)]

5. Previous Investigations (Resonance)
18F
17O+p
Ep= 193keV
5789
1080
937
Ex(keV)
ωγ193= (1.2±0.2)×10-6 eV [Fox et al. Phys. Rev. C 71, (2005)]
ωγ193= (2.2±0.4)×10-6 eV [Chafa et al. Phys. Rev. C 75, (2007)]
Clear discrepancy between measurements

6. Aims of Our Investigation
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.
To Measure:
Measurements made using both prompt-gamma and activation techniques.

7. The LUNA Accelerator at Gran Sasso
~1400 m

8. 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

9. Oxygen Enriched Targets
Strong 18O resonance used to monitor target degradation
19F
18O+p
Ep = 151 keV
8137
3908
Eγ=4.2 MeV
Ex(keV)
Fresh Target
10C
23C
38C
also studied with SIMS and RBS measurements.

10. On and Off Resonance Spectra
On-Resonance
On-Resonance
Off-Resonance

11. New Transitions Observed
18F
17O+p
Ep= 193 keV
5789
1080
937
3839
3791
3358
3134
2523
2101
1041
Ex(keV)
Black = Previously Observed
Blue = First Observation

12. Coincidence Summing Summing-in for 3 ∝B1B2ε1ε2
Intensity
Including summing effects
No summing effects
Energy
Summing-in for 3 ∝B1B2ε1ε2
summing-out for 1 ∝B1B2ε1εT2
Simple decay cascade => summing effects generally small

13. Analysis complete. Paper in preparation for publication.
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.

14. 17O(p,α)14N reaction in competition with 17O(p,γ)18F
The 17O(p,α)14N Reaction
(p,γ)
(β+ν)
(p,α)
17O
18F
14N
13C
13N
12C
15N
16O
18O
15O
17F I II
III
17O(p,α)14N reaction in competition with 17O(p,γ)18F

15. 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) – 15]
(1.7±0.15 x10-3 eV [Moazen et al PRC 75 (2007) – 7]
(1.66±0.17) x10-3 eV [Newton et al PRC 75 (2007) – 4]
Ep = 70 keV resonance strength:
Berheide et al ZPhys A 343 (1992)
Blackmon PRL 74 (1995)
Sergi et al PRC 82 (2010) (R)

16. Experimental Setup
Beam
Target
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)

17. First Spectra Acquired
18O Resonance Scan
Detector Calibration
~2.8 MeV α
18O(p,α)15N

18. 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