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Underground Measurement of the 17O+p Reactions

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Presentation on theme: "Underground Measurement of the 17O+p Reactions"— Presentation transcript:

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

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