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A new approach to the 176 Lu puzzle

A new approach to the 176 Lu puzzle. clock or thermometer? an astrophysical quest and a nuclear challenge 20 years of nuclear physics level schemes, cross sections, IR finally the Torino solution. p process. Hf. 176. 151. Lu. 176. t 1/2 = 36 Gyr !!. 152. 154.

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A new approach to the 176 Lu puzzle

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  1. A new approach to the 176Lu puzzle • clock or thermometer? an astrophysical quest and a nuclear challenge • 20 years of nuclear physics level schemes, cross sections, IR • finally the Torino solution

  2. p process Hf 176 151 Lu 176 t1/2 = 36 Gyr !! 152 154 179 180 Yb s process 175 174 176 177 178 r process the s-process branching at 176Lu

  3. Audouze, Fowler, & Schramm identify 176Lu as a cosmic clock (1972) ?

  4. the clock is challenged by Richard Ward (1980)

  5. induced transitions by thermal photons? 180 179 178 177 176 174 175 r process life is never easy p process Hf 176 151 Lu 3.7 h 152 154 36 Gyr Yb s process lots of nuclear input: (1) lb of 176Lu under stellar temperatures (2) (n,g) cross sections for s-process flow (3) isomeric ratio

  6. Hf 176 Lu 3.7 h 36 Gyr m Yb 175 174 176 177 178 (1) 176Lu decay i gs are isomer and ground state connected at high T ?

  7. Hf 176 Lu 3.7 h 36 Gyr Yb 175 174 176 177 178 fn,eff fn(nn, T) GAMS spectrometry at ILL Grenoble first mediating level at 838 keV !

  8. low mass AGB stars – the main s component in 1999

  9. (n,g): n-beam p-beam Pb neutron target sample (2) stellar (n,g) cross sections TOF with total absorption calorimeter @ FZK • 40 BaF2 crystals • 12 pentagons & 28 hexagons • 15 cm crystal thickness

  10. accurate (n,g) cross sections at FZK • measureds(En) by time of flight, 3 < En < 225 keV for all Yb, Lu, and Hf isotopes to ±1%, • determined Maxwell-average for stellar spectrum

  11. 3.7 h b g activation in quasi-stellar spectrum 7Li(p,n)7Be kT=25 keV 18O(p,n)18F kT=5 keV (3) partial cross section to isomer isomeric ratio = (s to isomer) / stot

  12. spectrum after irradiation 176Lum 176Lug isomeric ratio gamma spectroscopy with HPGe detector

  13. branching factor fn (nn, T) • level scheme of 176Lu • + • MACS to ± 1% for • 174Yb, 176Yb • 175Lu, 176Lu • 176Hf, 177Hf, 178Hf… • + • IR(176Lu) @ kT= 5 keV • kT=25 keV 3 1010 cm-3 3 109 cm-3 3 108 cm-3 fn chosen for 6 different neutron density situations throughout each thermal pulse covering a range 0.20 < fn < 0.92 improved nuclear physics input and refined low mass AGB star model

  14. Hf 176 177 178 Lu h 175 Gyr Yb 174 176 176Hf 176Hf 176Lu 176Lu s production of 176Lu and 176Hf during and between thermal pulses

  15. 1999 OVERABUNDANCES NORMALIZED TO 151Sm ATOMIC MASS the main s component (in %) 1999 176Lu 90 176Hf 113 2006 104 96 after 5Gyr 96 97

  16. the abundance ratio 176Lu/176Hf is determined by interplay of several nuclear physics features with the stellar environment • decay rate, cross sections, isomers T(t) and nn(t) • this interplay is so complex that the chance to obtain the correct answer simply by “ben trovare“ is negligible • in a wider context this holds also for similar independent s-process branchings; hence these cases provide the most crucial test for stellar models of the AGB phase summary

  17. Karlsruhe: C. Arlandini, H. Beer, S. Dababneh, M. Heil, N. Klay, R. Plag, R. Reifarth, G. Schatz, F. Voss, N. Winckler, K. Wisshak Grenoble: H. Börner, C. Doll, F. Hoyler, B. Krusche, S. Robinson, K. Schreckenbach Munich: U. Mayerhofer, G. Hlawatsch, H. Lindner, T. von Egidy Basel: T. Rauscher Sofia: W. Andrejtscheff, P. Petkov Obninsk: L. Kazakov Prague: F. Becvar, M. Krticka Chicago: A. Davis Beijing: W. Zhao Teramo: O. Straniero Torino: S. Bisterzo,M. Busso, R. Gallino

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