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The neutron capture cross section of the s-process branch point 63Ni

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1 The neutron capture cross section of the s-process branch point 63Ni
INTC-P-283 The neutron capture cross section of the s-process branch point 63Ni Spokespersons: C. Lederer, C. Massimi, Technical Coordinator: V. Vlachoudis M. Barbagallo, F. Belloni, E. Berthoumieux, M. Calviani, D. Cano-Ott, N. Colonna, I. Dillmann, K. Fraval, C. Guerrero, F. Gunsing, F. Käppeler, A. Mengoni, G. Tagliente, J.L. Tain, A. Wallner, and the n_TOF Collaboration n_TOF collaboration meeting, , Seville

2 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Introduction Claudia Lederer n_TOF collaboration meeting, , Seville

3 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Motivation How are heavy elements formed (>Fe) ? Abundance (Si=106) mass number Claudia Lederer n_TOF collaboration meeting, , Seville

4 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Motivation How are heavy elements formed (>Fe) ? dominantly via neutron capture reactions BB fusion neutrons Abundance (Si=106) mass number Claudia Lederer n_TOF collaboration meeting, , Seville

5 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Motivation How are heavy elements formed (>Fe) ? dominantly via neutron capture reactions slow neutron capture (s-process) rapid neutron capture (r-process) BB fusion neutrons Abundance (Si=106) mass number Claudia Lederer n_TOF collaboration meeting, , Seville

6 Neutron capture processes
slow neutron capture (s-process) AGB stars, massive stars tn,g (~1 yr) > t1/2 Nn~108 cm-3 close to valley of stability nuclear physics input: <sn,g >, t1/2 rapid neutron capture (r-process) explosive scenarios tn,g (10-4s) < t1/2 Nn~1021 cm-3 far from valley of stability these 2 processes can explain almost all isotopic signatures !! F. Käppeler, A. Mengoni, Nucl. Phys. A 777 (2006) Claudia Lederer n_TOF collaboration meeting, , Seville

7 Neutron capture processes
slow neutron capture (s-process) AGB stars, massive stars tn,g (~1 yr) > t1/2 Nn~108 cm-3 close to valley of stability nuclear physics input: <sn,g >, t1/2 rapid neutron capture (r-process) explosive scenarios tn,g (10-4s) < t1/2 Nn~1021 cm-3 far from valley of stability Maxwellian Averaged Cross Section (MACS) these 2 processes can explain almost all isotopic signatures !! F. Käppeler, A. Mengoni, Nucl. Phys. A 777 (2006) Claudia Lederer n_TOF collaboration meeting, , Seville

8 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
s-process main s-process: Zr < A < Bi in thermally pulsing AGB stars after He core burning (1-3 M); kT= 8 keV, 23 keV Local equilibrium N<sn,g>=const. between neutron shell closures s-only main: N<sn,g>= const F. Käppeler, Prog. Part. Nucl. Phys. 43 (1999) Claudia Lederer n_TOF collaboration meeting, , Seville

9 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
s-process main s-process: Zr < A < Bi in thermally pulsing AGB stars after He core burning (1-3 M); kT= 8 keV, 23 keV Local equilibrium N<sn,g>=const. between neutron shell closures weak s-process: additional component for Fe < A < Zr in massive stars (> 8 M); kT= 25 keV, 91 keV neutron fluence too small for equilibrium s-only weak+main main: N<sn,g>= const F. Käppeler, Prog. Part. Nucl. Phys. 43 (1999) Claudia Lederer n_TOF collaboration meeting, , Seville

10 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Propagation effect of cross section: 62Ni(n,g) MACS at 30 keV 25 M 35 mb 22.6 mb 12.5 mb H. Nassar et al., Phys. Rev. Lett. 94 (2005) mass number Claudia Lederer n_TOF collaboration meeting, , Seville

11 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Propagation effect of cross section: 62Ni(n,g) MACS at 30 keV 25 M 35 mb 22.6 mb 12.5 mb H. Nassar et al., Phys. Rev. Lett. 94 (2005) mass number capture cross section influences abundances of all following isotopes up to A~90 ! MACS needed up to ~100 keV ! Claudia Lederer n_TOF collaboration meeting, , Seville

12 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
The case of 63Ni t1/2=100.1 yr decay: b- to 63Cu (no g-emission  no radioactive background) t1/2 reduced under stellar conditions  for kT=91 keV, t1/2= 0.4 yr ! (Pignatari et al. Ap.J. 710 (2010)) Claudia Lederer n_TOF collaboration meeting, , Seville

13 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
The case of 63Ni t1/2=100.1 yr decay: b- to 63Cu (no g-emission  no radioactive background) t1/2 reduced under stellar conditions  for kT=91 keV, t1/2= 0.4 yr ! (Pignatari et al. Ap.J. 710 (2010)) Courtesy of I. Dillmann core He burning, kT=25 keV, Nn~106 cm-3 C shell burning, kT=91 keV, Nn~1011 cm-3 Claudia Lederer n_TOF collaboration meeting, , Seville

14 Present situation on 63Ni(n,g)
measurements so far ONLY at thermal energies MACS are based on extrapolation of these cross sections  theoretical assumptions could be affected by big uncertainties Claudia Lederer n_TOF collaboration meeting, , Seville

15 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
63Ni cross section according to calculations: This work: estimate of cross section by generating artificial set of resonances: fixed statistical properties of level spacing, neutron widths and gamma widths neutron strength functions and reaction widths close to exp. values of 62Ni (small variations for different Ni isotopes) procedure tested on stable Ni isotopes Claudia Lederer n_TOF collaboration meeting, , Seville

16 Present situation on 63Ni(n,g)
measurements so far ONLY at thermal energies MACS are based on extrapolation of these cross sections  theoretical assumptions could be affected by big uncertainties MACS at 30 keV: KADoNiS: ± 6 mb TENDL(2009): mb this work: mb Claudia Lederer n_TOF collaboration meeting, , Seville

17 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Measurement Claudia Lederer n_TOF collaboration meeting, , Seville

18 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
63Ni sample 3 metal discs (2 foils produced 1984, 1 foil produced 1992) total mass: mg diameter: mm enrichment in 63Ni: % (= 112 mg) contaminants: mg 63Cu  will be removed chemically at PSI part of sample at FZK: is on the way to PSI part of sample at LANL: will be sent to PSI these days Claudia Lederer n_TOF collaboration meeting, , Seville

19 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Count rate estimate based on calculated cross section described before Claudia Lederer n_TOF collaboration meeting, , Seville

20 63Ni distinguishable from 62Ni
Count rate estimate based on calculated cross section described before 63Ni distinguishable from 62Ni Claudia Lederer n_TOF collaboration meeting, , Seville

21 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Beam Time Request 112 mg 63Ni in sample 2009 campaign  2 g of 62Ni and 2x1018 protons 63Ni mass 20 times smaller BUT cross section higher according to calculations + reduced resolution acceptable less background at high neutron energies due to borated water  remeasurement of 62Ni for background determination runs with Au (normalization) and C (neutron scattering background) necessary Claudia Lederer n_TOF collaboration meeting, , Seville

22 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Beam Time Request 112 mg 63Ni in sample 2009 campaign  2 g of 62Ni and 2x1018 protons 63Ni mass 20 times smaller BUT cross section higher according to calculations + reduced resolution acceptable less background at high neutron energies due to borated water  remeasurement of 62Ni for background determination runs with Au (normalization) and C (neutron scattering background) necessary 5x1018 protons 4x Ni 1x Ni, Au, C Claudia Lederer n_TOF collaboration meeting, , Seville

23 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
5x1018 protons 4x Ni 1x Ni, Au, C Claudia Lederer n_TOF collaboration meeting, , Seville

24 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
5x1018 protons 4x Ni 1x Ni, Au, C Claudia Lederer n_TOF collaboration meeting, , Seville

25 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
Summary 63Ni represents the first branching point of the s-process path and knowledge of its (n,g) cross section is of great importance for nuclear astrophysics there are no experimental data of the 63Ni(n,g) cross section above thermal thermal cross section for 63Ni and 62Ni can be measured with upgraded DAQ unique 63Ni sample suitable for a time-of-flight measurement is available 5x1018 protons approved by INTC for this measurement Claudia Lederer n_TOF collaboration meeting, , Seville

26 n_TOF collaboration meeting, 15-17. 12. 2010, Seville
THANK YOU FOR YOUR ATTENTION ! Claudia Lederer n_TOF collaboration meeting, , Seville

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