Underground Measurement of the 17O(p,γ)18F Reaction
David Scott
On behalf of the LUNA collaboration
Astrophysical Motivation
•
Site: Classical Novae
•
Reaction: 17O(p,γ)18F
Hot-CNO Cycle
17O
(p,γ)
18F
(β+ν)
18O
•
•
•
Annihilation 511 keV gamma-rays following β+ decay of 18F (t1/2=110 mins)
Potential constraints on current novae models
17O(p,γ)18F also important in AGB stars
The 17O(p,γ)18F Reaction in Novae
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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
Aim: To calculate resonant and non-resonant reaction rate contributions by
measuring γ-ray yields
Previous Investigations
•
•
•
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Rolfs et al. Nuc. Phys. A217 29-70 (1973) – 1st investigation of the 17O(p,γ)18F reaction
Fox et al. Phys. Rev. C 71, 055801 (2005) – 1st 193 keV res. meas. : ωγ193= (1.2±0.2)×10-6 eV
Chafa et al. Phys. Rev. C 75, 033810 (2007) – Activation meas. :
ωγ193= (2.2±0.4)×10-6 eV
Newton et al. Phys. Rev. C 81, 045801 (2010)
The LUNA Accelerator at Gran Sasso
Cosmic Rays
~1400
m
~ … attenuation
~
More from M. Aliotta and
A. Guglielmetti …
2500 attenuation factor
Experimental setup
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400 kV electrostatic accelerator
Up to 400 keV protons with a maximum current ~400 μA
•
•
Enriched 17O targets on tantalum backings (prepared via anodization process)
~5cm of lead shielding surrounding detector
Some experimental challenges…
• Target degradation (due to high beam current)
• Coincidence Summing effects (due to close detector geometry)
Target Degradation
Strong 18O resonance used to monitor target degradation
Ex(keV)
Ep = 151 keV
18O+p
8137
Eγ=4.2 MeV
3908
19F
Reactions occurring
at front of target
Reactions occurring
at rear of target
Coincident 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
What we observed…
On Resonance Spectra
R -> 1080
R -> 937
Ex(keV)
Ep= 193 keV
5789
17O+p
937
3839
3791
1080
3358
3134
2523
2101
R -> 2101
R -> 3791
R -> 3133
1080
1041
937
18F
Preliminary results look promising
Further analysis required…
Non-resonant contribution
Fox
On-resonance (black) and offresonance (purple)
Energy region investigated at
LUNA: Ep = 185 – 390 keV
Ep = 200 keV
Ep = 228 keV
Ep = 185 keV (below resonance)
937 keV
LUNA
Ep = 197 keV
Ep = 221 keV
Summary & Outlook
•
17O(p,γ)18F
reaction investigated in the energy region important for
classical novae
• Both resonant and non-resonant γ-ray spectra acquired
• Many more transitions observed
• Much better sensitivity for DC transitions
Analysis in progress …
The Luna Collaboration
A.Formicola1, M.Junker1, M. Anders2, D. Bemmerer2, Z.Elekes2, C.
Broggini3, A. Caciolli3, R.Menegazzo3, C. Rossi Alvarez3, C. Gustavino4,
Zs.Fülöp5, Gy. Gyurky5, T. Szucs5, E.Somorjai5, O. Straniero6, C.Rolfs7,
F.Strieder7, H.P.Trautvetter7, F.Terrasi8, M. Aliotta9, D.Scott9, P.Corvisiero10,
P.Prati10, A.Guglielmetti11, M.Campeggio11, D. Trezzi11, G.Imbriani12,
V.Roca12, Di Leva13, G.Gervino14, C.Salvo15
1Laboratori
Nazionali del Gran Sasso, INFN, ASSERGI, 2Forschungszentrum Dresden-Rossendorf, Germany,
3INFN, Padova, Italy, 4INFN, Roma La Sapienza, Italy, 5Institute of Nuclear Research (ATOMKI), Debrecen,
Hungary, 6Osservatorio Astronomico di Collurania, Teramo, and INFN, Napoli, Italy, 7Ruhr-Universität Bochum,
Bochum, Germany, 8Seconda Università di Napoli, Caserta, and INFN, Napoli, Italy, 9The University of
Edinburgh, UK, 10Università di Genova and INFN, Genova, Italy, 11Università di Milano and INFN, Milano, Italy,
12Università di Napoli ''Federico II'', and INFN, Napoli, Italy, 13INFN, Napoli, Italy, 14Università di Torino and
INFN, Torino, Italy, 15INFN Genova & INFN Napoli, italy
Resonance Strength Measurement
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Thick target yield:
(2𝐽𝑅 + 1)
Γ𝑒𝑛Γ𝑒𝑥
𝜔𝛾 =
(2𝐽𝑡 + 1)(2𝐽𝑝 + 1) Γ
γ-ray
Yield
𝜔𝛾 = Ymax
Ymax
ER,lab
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Experimentally:
2 𝜖𝑒𝑓𝑓 𝑁𝑑𝑒𝑡
𝜔𝛾 =
𝜆 𝐵𝑊(𝜃) 𝑁𝑖𝑛𝑐
Proton Energy