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,

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Presentation transcript:

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

the s-process branching at 176 Lu Yb Lu Hf p process s process r process t 1/2 = 36 Gyr !!

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

the clock is challenged by Richard Ward (1980)

life is never easy lots of nuclear input: (1)  of 176 Lu under stellar temperatures (2) (n,  ) cross sections for s-process flow (3) isomeric ratio Yb Lu Hf p process s process r process h 36 Gyr induced transitions by thermal photons?

(1) 176 Lu decay are isomer and ground state connected at high T ? i gs m Yb 176 Lu Hf h 36 Gyr

GAMS spectrometry at ILL Grenoble first mediating level at 838 keV ! f n,eff f n (n n, T) Yb 176 Lu Hf h 36 Gyr

low mass AGB stars – the main s component in 1999

(2) stellar (n,  ) cross sections 40 BaF 2 crystals 12 pentagons & 28 hexagons 15 cm crystal thickness sample Pb neutron target p-beam n-beam (n,  ): TOF with total absorption FZK

accurate (n,  ) cross sections at FZK  measured  (E n ) by time of flight, 3 < E n < 225 keV for all Yb, Lu, and Hf isotopes to ±1%, determined Maxwell-average for stellar spectrum

3.7 h (3) partial cross section to isomer isomeric ratio = (  to isomer) /  tot  activation in quasi-stellar spectrum 7 Li(p,n) 7 Be kT=25 keV 18 O(p,n) 18 F kT=5 keV 

gamma spectroscopy with HPGe detector isomeric ratio spectrum after irradiation 176 Lu m 176 Lu g

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

s production of 176 Lu and 176 Hf during and between thermal pulses Yb 176 Lu Hf h Gyr 176 Lu 176 Hf 176 Lu 176 Hf

the main s component (in %) Lu Hf 113 ATOMIC MASS OVERABUNDANCES NORMALIZED TO 151 Sm after 5Gyr 96 97

summary the abundance ratio 176 Lu/ 176 Hf is determined by interplay of several nuclear physics features with the stellar environment decay rate, cross sections, isomers T(t) and n n (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

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