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-capture measurements with the Recoil-Separator ERNA

This paper discusses the importance of accurate measurements for the 12C(α,γ)16O reaction, a key process in stellar helium burning. The Experimental Recoil Separator ERNA is presented as a new approach for direct measurements, utilizing a gas target and recoil mass separation. The advantages, disadvantages, and technical aspects of ERNA are discussed, along with preliminary results and future plans.

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-capture measurements with the Recoil-Separator ERNA

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  1. -capture measurements with theRecoil-Separator ERNA Frank Strieder Institut für Physik mit Ionenstrahlen Ruhr-Universität Bochum HRIBF Workshop – Nuclear Measurements for Astrophysics October 23-24, 2006, Oak Ridge, Tennessee

  2. 12C(,)16O the Holy Grail of Nuclear Astrophysics e 3He(,)7Be pp chain e

  3. low-energy tail of broad resonance Er Danger of Extrapolation Important for Experiments S(E)-FACTOR Low energy High energy S(E) extrapolation or measurements ? direct measurement LINEAR SCALE non resonant process sub-threshold resonance -Er 0 interaction energy E DANGER OF EXTRAPOLATION !

  4. ERNA - Experimental approach Pro & Cons A different approach: recoil mass separator Cn+ B A detection  A C purification detection separation coincidence Requirements Advantages Disadvantages • low background • high detection efficiency • measure stot • background free g-ray spectra • gas target • beam purification • 100% transmission for the • selected charge state • high suppression of the incident beam • inverse kinematics (gas target) • difficult to do • commissioning • charge state • beam intenity ?

  5. g-Recoil Coincidences Separation Detection & Identification projectiles Recoils + Recoils projectiles focusing prec = pproj momentum conservation g-ray emission  Recoil cone ERNA - Experimental approach He target projectiles Minimum supression factor with s = 10nbarn, ntarget=1x1018at/cm² Nproj / Nrecoils~ 1x1014

  6. ERNA - Experimental approach Setup ion source dynamitrontandem accelerator recoil focussing D E - E telescope He magnetic Gastarget Wien filter qu adrupole multiplets analysing doublet triplet magnet singlet ion beam Wien filter purification Wien filter side 60° magnet Wien filter FC recoil separation

  7. characteristics: • angular acceptance  32 mrad for 16O at Elab=3.0 – 15.0MeV for the total length of the gas target • energy acceptance  10% for 16O at Elab=3.0 – 15.0 MeV • suppression of incident beam (10-10 - 10-12)·10-2 (IC) => smin< 1 nb • purification of incident beam < 10-22 • resolution of ion chamber  250·A keV or combination E-silicon strip detector • layout COSY Infinity (recoils fit in 4” beam tube) • field settings are not calculated, but tuned

  8. Experimental approach: ERNA Gas target Gas pressure profile: 7Li(a,ag)7Li + energy loss of: 14N, 12C, 7Li

  9. ERNA - Experimental approach Charge State Distributions measured for entire energy range 4He gas 12C beam but question about point of origin in the gas target → no equilibrium

  10. ERNA - Experimental approach Setup Solution: a post-target-stripper • First test with laser ablated carbon foil: 12C(12C,8Be)16O • Final configuration: Ar post-target stripper after the 4He target to the separator 4He Ar 3He(,)7Be no post-target-stripper – measure all charge states

  11. ERNA - Experimental approach Setup Angular acceptance along the gas target central position upstream position upstream position(energy acceptance) beam diameter 4He gas 12C beam separator full angular acceptance  100 % transmission (better 3) over the total gas target length and full beam diameter

  12. ERNA - Experimental approach Setup Angular acceptance along the gas target Simulation ofrecoil cone - +

  13. ERNA Motivation Helium Burning Stellar Helium burning: 12C(a,g)16O Main reactions: 3a12C and 12C(a,g)16O 4He Red Giant 12C/16O abundance ratio triple alpha 12C Subsequent stellar evolution and nucleosynthesis 4He 12C(a,g)16O but 16O E0~ 300 keV, very low cross section Accurate measurements at higher energy and extrapolation to E0 are needed

  14. ERNA E/E Matrix 12C(a,g)16O Ecm=2.5 MeV SuppressionR~8*10-12

  15. ERNA Cross Section Curve RESULTS

  16. ERNA astrophysical S Factor RESULTS

  17. 12C(,)16O the Holy Grail of Nuclear Astrophysics e 3He(,)7Be pp chain e

  18. solar spy = solar neutrinos Explanation of Stars 1960‘s Davis, Fowler & Bahcall Homestake Experiment H Hydrogen Burning 4p  4He + 2 + 2e- Neutrino spectroscopy ? Sun = calibrated source

  19. ERNA Motivation Neutrino Spectroscopy Influence of different sources of uncertainties on the neutrino flux D(L  ) = 0.4 % D(age ) = 0.4 % D(Z/H ) = 3.3 % D(p-p) = 2 % D(3He+3He) =6 % D(3He+4He) =15 % D(7Be+p) = 10 %

  20. ERNA Motivation Neutrino Spectroscopy Influence of different sources of uncertainties on the neutrino experiment

  21. two types of  rays are used to measure 3He(,)7Be cross section 2 7/2- 4.57 7/2- 4.63 Ecm(MeV) Capture -rays: 0,1,429 1 0 1 Q= 1.586MeV Delayed - rays:: 7Be decay: 478 3He+4He 1/2- 429 3/2- 10.52% 1/2- 7Be 478 89.48% 3/2- T½ =53.3d 7Li

  22. Summary for the S34(0) values

  23. ERNA Acceptance 3He(,)7Be

  24. ERNA E/E Spectra 3He(,)7Be Ecm=1.8 MeV Inverse kinematics

  25. ERNA astrophysical S Factor RESULTS Preliminary result

  26. ERNA – present status • 12C(,g)16O Ecm>1.9 MeV (1.3 MeV) • 3He(a,g)7Be Ecm>1.1 MeV (0.6 MeV) ERNA - future plans and other perspectives • 3He(a,g)7Be -  measurement (free & coincidences) • 12C(,g)16O -  measurement (jet gas target) • 14N(a,g)18F • d(a,g)6Li

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