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ALNA- Accelerator Laboratory for Nuclear Astrophysics Underground

ALNA- Accelerator Laboratory for Nuclear Astrophysics Underground. Heide Costantini University of Notre Dame, IN, USA INFN, Genova, Italy. Outline:. Nuclear astrophysics: - main reactions - experimental problems. LUNA:

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ALNA- Accelerator Laboratory for Nuclear Astrophysics Underground

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  1. ALNA- Accelerator Laboratory for Nuclear Astrophysics Underground Heide Costantini University of Notre Dame, IN, USA INFN, Genova, Italy

  2. Outline: • Nuclear astrophysics: • - main reactions • - experimental problems • LUNA: • - an example of experimental nuclear astrophysics laboratory UNDERGROUND • ALNA: • goal • methods • experimental techniques

  3. the ambitious task of Nuclear Astrophysics is to explain the origin and relative abundance of the elements in the Universe Charged particles Fusion reactions 1010 108 106 relative abundance 104 n-capture, -decay,… N-ToF, RIA 102 Fe 1 10-2 0 10 20 30 40 50 60 70 80 90 Atomic number the abundance of the elements in the Universe elements are produced inside stars during their life

  4. Hydrogen burning p, 12C 13N p + p d + e+ + ne - p, d + p 3He + g pp chain CNO cycle 84.7 % 13.8 % 15N 13C 3He +3He a + 2p 3He +4He 7Be+g p, + 0.02 % 13.78 % 15O 14N 7Be+e- 7Li+g +ne 7Be +p 8B+g p, 7Li +p a + a 8B 2a + e++ ne produces energy for most of the life of the stars 4p  4He + 2e+ + 2e + 26.73 MeV

  5. Helium burning 4He 4He Triple  12C(,)16O 16O(,)20Ne 16O 12C 20Ne 4He Two questions remain relevant: Energy production and timescale: 4He(2,)12C(,)16O(,)20Ne Neutron production for weak s-process: 14N(,)18F(+)18O(,)22Ne(,n) 22Ne(,) Neutron production for fast s-process: 13C(,n)

  6. The extrapolation problem extrapolation is needed…. ? sometimes extrapolation fails !! S(E) factor ? ? (E) = S(E)·exp(-2) /E S(E) = E·(E)·exp(2) 2 = 31.29 Z1 Z2 (/E)0.5

  7. Environmental radioactivity has to be considered underground (shielding) and intrinsic detector bck Beam induced bck from impurities in beam & targets  high purity and detector techniques (coincidence) 3MeV < Eg < 8MeV 0.0002 Counts/s 3MeV < Eg < 8MeV: 0.5 Counts/s HpGe GOING UNDERGROUND Cross section measurement requirements Rlab> Bcosm+ Benv+Bbeaminduced

  8. Laboratory forUnderground Nuclear Astrophysics LUNA 1 (1992-2001) 50 kV LUNA 2 (2000…) 400 kV LUNA site LNGS (shielding  4000 m w.e.)

  9. Measurements @ LUNA p, 12C 13N p + p d + e+ + ne - p, d + p 3He + g pp chain CNO cycle 84.7 % 13.8 % 15N 13C 3He +3He a + 2p 3He +4He 7Be+g p, + 0.02 % 13.78 % 15O 14N 7Be+e- 7Li+g +ne 7Be +p 8B+g p, 7Li +p a + a 8B 2a + e++ ne 3He(4He,)7Be 3He(3He,2p)4He 14N(p,)15O d(p,)3He

  10. LUNA II U = 50 – 400 kV I  500 A for protons I  250 A for alphas Energy spread  70eV Long term stability: 5 eV/h

  11. 14N(p,)15O Q = 7.3 MeV 14N+p 7556 278 1/2 + 7297 7/2 + 7276 6859 5/2 + gas target -21 6793 3/2 + 3/2 - - 504 6176 5/2 + 5241 1/2 + 5183 beam 1/2 - 0 15O BGO summing crystal Spectrum 70 keV t = 49.12 days Q = 9277 C Reaction Rate = 10.95  0.83 c/d Background rate = 21.14  0.75 c/d

  12. LUNA main results 3He(3He,2p)4He 14N(p,)15O • Lowest energy: 2cts/month • Lowest cross section: 0.02 pbarn • Background < 4*10-2 cts/d in ROI Low cosmic background High beam current full advantage Underground lab High efficiency detector Pure gas target Event identification

  13. Goal at ALNA: Accelerators: installation of a small (2 MV terminal Voltage) accelerator to study (,n) and (,) reactions in forward kinematics • 1st phase: • 2nd phase: heavy ion accelerator for inverse kinematics studies (M. Couder’s talk) • systematic study of reactions relevant for the understanding of He-burning and C-burning in red giants, AGB stars and late evolutionary stages

  14. energy calibration: < 0.1% • Energy resolution: < 0.1% • long-term stability: > days to months • beam intensity: I > 100 A • Energy range: 100kV-2MV • Beam: p,  • Count rate limitation • of 1 ev/day > 0.2 nbarn 1st phase Accelerator Requirements

  15. high efficiency  increase counting rate • Low intrinsic activity • Passive shielding • event identification • active shielding decrease environmental background decrease beam-induced background Example: 19F(p,-)16O background reduction by Q-value gating for 19F(p,)20Ne counts counts E E 1st phase Detector facility requirements

  16. Facility requirements • Depth shielding  4000 (mwe) • Space 15X10X5 (m3) accelerator • 15x10x5 (m3) (target room 1st phase) • 15X20X5 (m3) (target room 2nd phase) • Electrical power50 kW (1st phase) • 200 kW (2nd phase) • Additional facilities machine shop • power supply • low level counting • DI water system • compressed air • LN2 • 5 ton crane in target area

  17. Contributors and collaborators: A. Champagne University of North Carolina R. Clark LBNL M. Couder University of Notre Dame M. Cromaz LBNL A. Garcia University of Washington J. Görres University of Notre Dame U. Greife Colorado School of Mines C. Iliadis University of North Carolina D. Leitner LBNL P. Parker Yale University K. Snover University of Washington P. Vetter LBNL M Wiescher University of Notre Dame

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