Underground Measurement of the 17 O+p Reactions David Scott On behalf of the LUNA collaboration...
-
Upload
kimberly-spark -
Category
Documents
-
view
212 -
download
0
Transcript of Underground Measurement of the 17 O+p Reactions David Scott On behalf of the LUNA collaboration...
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