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Nuclear physics aspects of neutron capture and β-decay rates in stellar environment

This article discusses the neutron capture and β-decay rates in nuclear physics, specifically focusing on their relevance in the stellar environment. It explores the s-process nucleosynthesis and provides information on the Os, Re, and W isotopes. Theoretical predictions, experimental data, and their impact on stellar corrections are also discussed.

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Nuclear physics aspects of neutron capture and β-decay rates in stellar environment

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  1. Nuclear physics aspectsof neutron capture and β-decay rates in stellar environment A Mengoni ENEA and INFN Bologna PANDORA meeting, 31 January 2019, Bologna

  2. s-process nucleosynthesis BANG! ? 4.6 Ga Now s-only Os Os 184 0.02 Os 185 94 d Os 186 1.58 Os 187 1.6 Os 188 13.3 Os 189 16.1 Os 190 26.4 Os 191 15.4 d Os 192 41.0 Re Re 183 71 d Re 184 38 d Re 185 37.4 Re 186 90.64 h Re 187 62.6 Re 188 16.98 h Re 189 24.3 h Re 190 3.1 m 42.3x109 a W 182 26.3 W 183 14.3 W 184 30.67 W 185 75.1 d W 186 28.6 W 187 23.8 h W 188 69 d W s-process r-only r-process (*) DD Clayton, ApJ 139 (1964) 637 >>

  3. n_TOF-04: 186Os capture x-section NB: the calculation is normalized NOT fitted to experimental data M Mosconi et al. (The n_TOF Collaboration), Physical Review C 82, 015802 (2010) – I M Mosconi et al. Physical Review C 82, 015803 (2010) – II K Fujii et al. (The n_TOF Collaboration), Physical Review C 82, 015804 (2010) – III www.cern.ch/n_TOF The n_TOF Collaboration

  4. n_TOF-04: 187Os capture x-section NB: the calculation is normalized NOT fitted to experimental data M Mosconi et al. (The n_TOF Collaboration), Physical Review C 82, 015802 (2010) – I M Mosconi et al. Physical Review C 82, 015803 (2010) – II K Fujii et al. (The n_TOF Collaboration), Physical Review C 82, 015804 (2010) – III www.cern.ch/n_TOF The n_TOF Collaboration

  5. 186Os capture x-section Hauser-Feschbach theory: (statistical model) • Neutron transmission coefficients, Tn : • from OMP calculations • g-ray transmission coefficients, Tg: • from GDR (experimental parameters) • Nuclear level densities: • fixed at the neutron binding from <D>exp www.cern.ch/n_TOF

  6. Thermal population of nuclear excited states 186Os 187Os 188Os in 187Os at kT = 30 keV: P(gs) = 33% P(1st) = 47% P(all others) = 20% stellar enhancementfactor SEF = s* / sexp SE Woosley and WA Fowler, ApJ 233 (1979) 411

  7. Stellar 187Os(n,g) rate 187Os at kT = 30 keV: P(gs) = 33% P(1st) = 47% P(all others) = 20% • Include thermal population • Include super-elastic scattering channels • Nuclear structure effects (deformation) <sn,g>* = SEF∙ <sn,g> SE Woosley and WA Fowler, ApJ 233 (1979) 411 alberto.mengoni@cern.ch

  8. Stellar enhancement factor Good news: Lab cross sections measured Compound system is the same Physical Review C 82, 015802 (2010) – I Physical Review C 82, 015803 (2010) – II Physical Review C 82, 015804 (2010) – III

  9. How accurate are theoretical predictions? 176Hf, 178Hf, 180Hf: MACS uncertainties 1 - 2% exercisejoined by 6 leadinggroups: calculate MACS of 174Hf and182Hf priortomeasurement C. Vockenhuber, I. Dillmann, M. Heil, F. Käppeler et al. (2007), Phys. Rev. C 75, 015804 … but: theory indispensable for stellar corrections!

  10. 187Re(b-) decay

  11. 187Re(b-) decay The b-decay half-life of 187Re is tb=43.2  1.3 Gyr. Under stellar conditions, the 187Os and 187Re atoms can be partly or fully ionized. The b-decay rate can then proceed through a transition to bound-electronic states in 187Os. The rate for this process can be orders of magnitude faster than the neutral-atom decay. The bound-state b-decay half-life of fully-ionized 187Re has been measured @ GSI. The half-life of fully-ionized 187Re turns out to be: tb=32.9  2.0 yr. (F. Bosch, et al., PRL 77 (1996) 5190) Impact on the age: up tp1 Gyr

  12. What about theory? Nuclear beta-decays of highly ionized heavy atoms in stellar interiorsK Takahashi and K Yokoi Nuclear Physics A404, 578 (1983) Beta-decay rates of highly ionized heavy atoms in stellar interiorsK Takahashi and K Yokoi Atomic Data and Nuclear Data Tables 36, 375 (1987)

  13. Extrapolations & interpolations Re187(𝛽-)

  14. Extrapolations & interpolations Re187(𝛽-)

  15. What about theory? Saha equations for ionized state populations: number density of element- in its -times ionized state atomic partition function atomic mass ionization potential degeneracy parameter

  16. What about theory? Classification of transitions

  17. n_TOF experiments U Abbondanno et al. - The n_TOF Collaboration Phys. Rev. Lett. 93 (2004), 161103 152Gd 153Gd 239.47 d 154Gd 155Gd 156Gd 157Gd Gd Eu 151Eu 152Eu 9 h 153Eu 154Eu 8.8 a 155Eu 4.761 a 156Eu 15.2 d 150Sm 151Sm93 a 152Sm 153Sm 42.27 h 154Sm Sm • branching isotope in the Sm-Eu-Gd region: • test for low-mass TP-AGB • branching ratio (capture/b-decay) provides infos on the thermodynamical conditions of the s-processing (if accurate capture rates are known!) The n_TOF Collaboration

  18. Implications Using the “classical” s-process model we obtain T8 > 4incompatible with realistic He-shell burning conditions 95% of neutrons are produced by 13C(a,n) at kT~ 8 keV. Under these conditions, 152Gd cannot be produced During the He-burning episode the 22Ne(a,n) is activated at kT~ 23 keV. The 151Sm b-decay is fast enough to produce 70% of observed 152Gd (solar) • Present main uncertainties: • lb(T) of 151Sm • stellar capture rate Inverse reactions

  19. 151Sm at n_TOF U Abbondanno et al. - The n_TOF Collaboration, Phys. Rev. Lett. 93 (2004), 161103 The n_TOF Collaboration

  20. Capture 151Sm 204,206,207,208Pb, 209Bi 232Th 24,25,26Mg 90,91,92,94,96Zr, 93Zr 139La 186,187,188Os 233,234U 237Np,240Pu,243Am Fission 233,234,235,236,238U 232Th 209Bi 237Np 241,243Am, 245Cm n_TOF experiments U Abbondanno et al. - The n_TOF Collaboration Phys. Rev. Lett. 93 (2004), 161103 n_TOF MACS-30 = 3100 ± 160 mb <D0> = 1.48 ± 0.04 eV, S0 = (3.87 ± 0.20)×10-4 The n_TOF Collaboration

  21. 151Sm(b-) decay ne = 10+26 [1/cm3]

  22. 151Sm(n,g): lab Hauser-Feshbach theory: average over many compound states:

  23. 151Sm(n,g)* at kT=30 keV Hauser-Feshbach theory: weighted sum over target excited states:

  24. 151Sm(n,g)*:predictions • up to 10 excited levels included • super-elastic scattering included

  25. 151Sm(n,g)* & 152Sm dissociation at kT=30 keV Hauser-Feshbach theory: weighted sum over target excited states:

  26. 152Sm(g,n)151Sm* • The measurement could done by activation • g-rays from bremstralung spectra with different end-point energies • 1st excited states dominant for 100 keV

  27. End

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