Neutron physics of the Re/Os clock. III. Resonance analyses and stellar (n,γ) cross sections ofOs186,187,1

Abstract

Neutron resonance analyses have been performed for the capture cross sections of 186 Os, 187 Os, and 188 Os measured at the n TOF facility at CERN. Resonance parameters have been extracted up to 5, 3, and 8 keV, respectively, using the SAMMY code for a full R-matrix fit of the capture yields. From these results average resonance parameters were derived by a statistical analysis to provide a comprehensive experimental basis for modeling of the stellar neutron capture rates of these isotopes in terms of the Hauser-Feshbach statistical model. Consistent calculations for the capture and inelastic reaction channels are crucial for the evaluation of stellar enhancement factors to correct the Maxwellian averaged cross sections obtained from experimental data for the effect of thermally populated excited states. These factors have been calculated for the full temperature range of current scenarios of s-process nucleosynthesis using the combined information of the experimental data in the region of resolved resonances and in the continuum. The consequences of this analysis for the s-process component of the 187 Os abundance and the related impact on the evaluation of the time duration of galactic nucleosynthesis via the Re/Os cosmochronometer are discussed.

Astrophysics at n_TOF Facility at CERN

“…With a schematic model that assumes an exponentially decreasing production rate for 187 Re, an age of the Universe of 14.94 Gyr was obtained from the Re/Os cosmo-cronometer, with an accuracy, mostly related to the remaining nuclear physics uncertainties, of less than 1 Gyr. More details can be found in [17,18,19,20] FIG. 1.…”

OPPORTUNITIES TO CONSTRAIN ASTROPHYSICAL REACTION RATES FOR THEs-PROCESS VIA DETERMINATION OF THE GROUND-STATE CROSS-SECTIONS

“…contribution reduces further to X = 0.28 for kT = 30 keV, although f SEF = 1.19 remains close to unity. Because of the relevance of this reaction to the Re/Os cosmochronometer, neutron-capture experiments on 187 Os have been performed (see, e.g., Mosconi et al 2010a;Fujii et al 2010, and references therein). The importance of the low-lying, first excited state was noticed in that work (Mosconi et al 2010b;Fujii et al 2010), and additional experiments on the inelastic neutron scattering of 187 Os and the photodisintegration of 188 Os have been performed (see, e.g., Shizuma et al 2005;Mosconi et al 2010b) to study transitions proceeding on this state.…”

Present status and future programs of the n_TOF experiment

“…Cortés-Giraldo 13) , M. Diakaki 14) , I. Dillmann 15) , C. Domingo-Pardo 16) , I. Duran 17) , N. Dzysiuk 18) , C. Eleftheriadis 19) , M. Fernández-Ordóñez 7) , A. Ferrari 1) , K. Fraval 9) , S. Ganesan 20) , G. Giubrone 21) , M.B. Gómez-Hornillos 11) , I.F.…”

“…Gómez-Hornillos 11) , I.F. Gonçalves 12) , E. González-Romero 7) , F. Gramegna 18) , E. Griesmayer 2) , C. Guerrero 1) , F. Gunsing 9) , M. Heil 16) , D.G. Jenkins 22) , E. Jericha 2) , Y. Kadi 1) , F. Käppeler 23) , D. Karadimos 24) , M. Kokkoris 14) , M. Krtička 8) , J. Kroll 8) , C. Lederer 25) , H. Leeb 2) , L.S.…”

“…Leong 4) , R. Losito 1) , M. Lozano 13) , A. Manousos 19) , J. Marganiec 3) , T. Martinez 7) , C. Massimi 26) , P.F. Mastinu 18) , M. Mastromarco 6) , M. Meaze 6) , E. Mendoza 7) , A. Mengoni 27) , P.M. Milazzo 28) , M. Mirea 5) , C. Paradela 17) , A. Pavlik 25) , J. Perkowski 3) , J. Praena 13) , J.M. Quesada 13) , T. Rauscher 29) , R. Reifarth 16) , A. Riego 11) , F. Roman 1,5) , C. Rubbia 1,30) , R. Sarmento 12) , G. Tagliente 6) , J.L.…”