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Underground Nuclear Astrophysics

L aboratory U nderground N uclear A strophysics. Underground Nuclear Astrophysics. Heide Costantini INFN, Genova, Italy University of Notre Dame, IN, USA. Outline. Reaction rate for H-burning. Why going underground ?. The LUNA project:. - Main nuclear reactions studied.

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Underground Nuclear Astrophysics

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  1. LaboratoryUndergroundNuclearAstrophysics Underground Nuclear Astrophysics Heide Costantini INFN, Genova, Italy University of Notre Dame, IN, USA

  2. Outline • Reaction rate for H-burning • Why going underground ? • The LUNA project: - Main nuclear reactions studied • Experimental techniques: • - detectors • targets • bck sources • Outlook

  3. 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

  4. Reaction rate for charged particles Z1Z2e2 tunneling probability  KT <<  RN EG E dE S(E) exp <v> = E KT 0 E0 3He(3He,2p)4He 22 keV 8 1  d(p,)3He 7 keV (KT)3/2 14N(p,)15O 27 keV (E) = S(E)·exp(-(EG/E)1/2)

  5. Reaction rate in the laboratory Rlab= ··Ip··Nav/A e ~ 10 % IP ~ mA  ~ mg/cm2 pb < s < nb event/month < Rlab < event/day (E) = S(E)·exp(-(EG/E)1/2) Extrapolation is needed !!

  6. 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

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

  8. 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(3He,2p)4He 50 KV 3He(4He,)7Be 400 KV d(p,)3He 14N(p,)15O 400 KV 50 KV

  9. 50 kV: LUNAI Energy spread: 20 eV keV/h

  10. 3He(3He,2p)4He Cosmic background suppression in silicon detector beam induced background 3He(d,p)4He. Coincidence between two Si detectors • Lowest energy: 2cts/month • Lowest cross section: 0.02 pbarn • Background < 4*10-2 cts/d in ROI windowless gas target

  11. 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

  12. 14N(p,)15O p, 12C 13N - p, Bottle neck of CNO cycle 15N 13C p, + 15O 14N p, Determination age of globular clusters Determination of CNO neutrino fluxes Turn-off luminosity Dredge-up efficiency in AGB stars F. Herwig and S. M. Austin. Astrophys. J., 612:L73, 2004.

  13. 14N+p 7556 278 1/2 + 7297 7/2 + 7276 6859 5/2 + -21 6793 3/2 + 3/2 - - 504 6176 Q = 7.3 MeV 5/2 + 5241 Angulo et al 2000 1/2 + 5183 factor 20 ! 15O 1/2 - 0 Stot(0) = 3.2  1.77 keV b 2 goals for underground measurement Single -transitions cross section contributions (high resolution) Total cross section at energies close to Gamow window (high efficiency) METHOD METHOD Solid target + HPGe detector Gas target + BGO summing crystal

  14. High resolution measurement 6.17 6.79 5.18 DC/0 126 % • purity and stability of solid targets  TiN deposited on Ta backing • Careful determination of summing effect due to close detector geometry • HpGe efficiency ~ 1% Emin=120 KeV

  15. High efficiency measurement • All the  cascades are summed together to a peak at E=Q+Ecm • windowless 14N gas target gas target beam • Ip~500 A  the beam heats the gas changing the local density • BGO efficiency in the ROI ~ 65% Emin= 70 KeV

  16. Q = 9277 C t = 49.12 days Reaction Rate = 10.95  0.83 counts/day Background rate = 21.14  0.75 counts/day Elab=80 keV

  17. Results Both results confirm the low reaction rate GC age increases of 0.7-1 Gyr • CNO neutrino flux decreases a factor  2

  18. If the Q-value of the nuclear reaction is < 3MeV, is it useless to go underground ? Cu The 3He(,)7Be cross section is the major nuclear physics uncertainty in the determination of the 8B-neutrinos flux p + p d + e+ + ne  d + p 3He + g pp chain 84.7 % 13.8 % Detectors can be shielded passively with proper Pb-Cu shield as on surface Pb The production of 7Li in BBN is very sensitive to 3He(,)7Be cross section. 3He +3He a + 2p 3He +4He 7Be+g Cu 0.02 % Det 13.78 % 7Be+e- 7Li+g +ne 7Be +p 8B+g 7Li +p a + a 8B 2a + e++ ne Ongoing experiment 3He(,)7Be Q = 1.6 MeV Environmental radioactivity is present underground (Rn) BUT underground passive shielding is more effective since  flux, that create secondary s in the shield, is suppressed.

  19. Q = 1.6 MeV Ecm J Ex(keV) 1586 DC 3He+ 3He(a,g)7Be 7Be+e7Li*(g)+e 429 1/2- 3/2- 0 7Be Eg=1586 keV + Ecm (DC  0); Eg= 1157 keV + Ecm (DC  429) Eg= 429 keV Eg = 478 keV 1/2- 478 EC 0 3/2- 7Li Cross sections measurements were performed: detecting the prompt  from -capture reaction detecting delayed  coming from 7Be decay The results from the two techniques show a 9% discrepancy GOAL AT LUNA:MEASUREMENT WITH BOTH METHODS AND WITH ACCURACY ~ 4-5 %

  20. Si monitor Activation method Online- method • 3He recirculating system • 135% HpGe detector in close geometry to target • 0.3 m3 Pb-Cu shield • suppression of natural bck: 10+5 • chamber in OFC to reduce background on • detector • 7Be nuclei collected on the beam stop • during online -measurement • 125% HpGe detector • Pb-Cu shield in low activity lab in LNGS • suppression of natural bck: 10+5 7Be- decay from activation measurement at E=350 keV On line -measurement E=400 keV T=4.5 d I=280 A 7Be+e7Li*()+e T=2 days 3He(,)7Be See poster by G. Gyürki on Thursday

  21. ECM (keV) Ex (keV) J 25Mg(p,)26Al solid target 1”x1”NaI(Tl) Cooling trap Motivations • Nucleosynthesis of the elements 24<A<27 • Astronomical interest of 1809 keV 26Al decay -line 4 BGO Detector 5+(4+) 190 6496 Novae explosive Burning (T9>0.1) 130 6436 4- 108 6414 0+ 93 6399 2- AGB or W-R Stars (T9~0.05) 6364 3+ 58 4- 37 6343 Q = 6306 keV 25Mg+p 6280 3+ -26 Astronomical interest: T9<0.2 EG<220 keV 26Alm 228 0+ 0 5+ 26Al0

  22. A working group inside LUNA is preparing a new proposal for the new LUNA phase Spokesperson: Carlo Broggini broggini@pd.infn.it What else can be done with LUNA II (400kV) ? maybe a new accelerator for He-burning key reactions?

  23. ALNA Idea of a new underground accelerator facility inside the DUSELlaboratory (Homestake (SD) or Henderson Mine (CO)) Focused mainly on study of He-burning and C-burning reactions • 1st phase: installation of a light ion (2 MV terminal Voltage) accelerator to study (,n) and (,) reactions in forward kinematics • 2nd phase: heavy ion accelerator for inverse kinematics studies Notre Dame Recoil Mass separator See J. Görres’ talk tomorrow!!

  24. LUNA ATOMKI : Debrecen INFN: Genova, Gran Sasso, Milano, Napoli, Padova, Torino Univ. Bochum Univ. Lisboa

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