Underground Measurement of the 17O+p Reactions

David ScottOn behalf of the LUNA collaboration

Carpathian SSP12

• Astrophysical Motivation• The 17O(p,γ)18F Reaction:

- Current Status- Present Investigation

• Future direction: The 17O(p,α)14N Reaction

• 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

Astrophysical Motivation

(p,γ)(β

+ν)

(p,α)17O 18F14N13C

13N

12C 15N 16O 18O

15O 17F CNO Cycle

I II III

(Cygni 1992)

• Classical novae T=0.1-0.4 GK => EGamow = 100 – 260 keV

• Resonant Contribution: 17O(p,γ)18F resonance at Ep = 193 keV

• Also Non-resonant Contribution

The 17O(p,γ)18F Reaction in Novae

18F

17O+p

Ep= 193keV 5789

1080

937

Gamow Peak

Ex(keV)

Previous Investigations (S-factor)

• 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)]

LUNA

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, 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

• 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.

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 TargetsStrong 18O resonance used to monitor target degradation

19F

18O+p

Ep = 151 keV 8137

3908

Eγ=4.2 MeV

Ex(keV)

Fresh Target

10C23C

38C

also studied with SIMS and RBS measurements.

On-Resonance

Off-Resonance

On-Resonance

Off-Resonance

On and Off Resonance Spectra

New Transitions Observed

18F

17O+p

Ep= 193 keV5789

1080

937

3839

3791

3358

3134

25232101

1041

Ex(keV)

Black = Previously ObservedBlue = First Observation

Coincidence Summing

• Summing-in for 3 • summing-out for 1

1

2

3

1 2 3

No summing effectsIncluding summing effects

Energy

Inte

nsity

Simple decay cascade => summing effects generally small

• 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.

Results

Analysis complete. Paper in preparation for publication.

The 17O(p,α)14N Reaction

(p,γ)

(β+ν)

(p,α)17O 18F14N13C

13N

12C 15N 16O 18O

15O 17F

I II III

17O(p,α)14N reaction in competition with 17O(p,γ)18F

The 17O(p,α)14N ReactionPrevious 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) 483-487Blackmon PRL 74 (1995) 2642-2645Sergi et al PRC 82 (2010) 032801(R)

Beam

Target

Outer Al DomeInner 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)

Experimental Setup

First Spectra Acquired

~2.8 MeV α

18O(p,α)15N

18O Resonance Scan 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, HungaryO. 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