APS/123-QED arXiv:1001.1906v1 [astro-ph.SR] 12 Jan 2010 $^{∗}$Electronic address: iris.dillmann@ph.tum.de; Previous addresses: Departement f¨ ur Physik, Universit¨ at Basel and Institut f¨ ur Kern- physik, Forschungszentrum Karlsruhe, D-76021 Karlsruhe. $^{†}$Previous address: Institut f¨ ur Kernphysik, Forschungszentrum Karlsruhe, D-76021 Karlsruhe. Stellar (n, γ ) cross sections of p -process isotopes Part 1: $^{102}$Pd, $^{120}$Te, 130 , $^{132}$Ba, and $^{156}$Dy I. Dillmann ∗ Physik Department E12 and Excellence Cluster Universe, Technische Universit¨ at M¨ unchen, Germany C. Domingo-Pardo † and M. Heil † Gesellschaft f¨ ur Schwerionenforschung Darmstadt, Germany S. Dababneh Faculty of Applied Sciences, Al-Balqa Applied University, Salt 19117, Jordan F. K¨ appeler and S. Walter Institut f¨ ur Kernphysik, Forschungszentrum Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany T. Rauscher and F.-K. Thielemann Departement Physik, Universit¨ at Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland (Dated: November 1, 2018) We have investigated the ( n, γ ) cross sections of p -process isotopes with the activation tech- nique. The measurements were carried out at the Karlsruhe Van de Graaff accelerator using the $^{7}$Li( p, n ) $^{7}$Be source for simulating a Maxwellian neutron distribution of kT = 25 keV. Stellar cross section measurements are reported for the light p -process isotopes $^{102}$Pd, $^{120}$Te, 130 , $^{132}$Ba, and $^{156}$Dy. In a following paper the cross sections of $^{168}$Yb, $^{180}$W, $^{184}$Os, $^{190}$Pt, and $^{196}$Hg will be discussed. The data are extrapolated to p -process energies by including information from evaluated nuclear data libraries. The results are compared to standard Hauser-Feshbach models frequently used in astrophysics. PACS numbers: 25.40.Lw, 26.30.-k, 27.50.+e, 97.10.Cv Astrophysical models can explain the origin of most nuclei beyond the iron group by a combination of pro- cesses involving neutron captures on long ( s -process) or short ( r -process) time scales [1, 2]. However, 32 proton-rich stable isotopes between $^{74}$Se and $^{196}$Hg cannot be formed in these neutron capture processes, because they are either shielded by stable iso- topes from the r -process decay chains or lie outside the s -process flow (Fig. 1). These isotopes, which are as- cribed to the so-called ” p -process”, are 10 to 100 times less abundant than their s - and r -process neighbors. So far, the astrophysical site of the p -process is still under discussion, since the solar p -abundances can not be com- pletely described by current models. Historically, the p -process was thought to proceed via proton captures, but a plausible site with the required amount of free protons could not be identified. Moreover, elements with large Z cannot be produced by proton cap- tures because the temperatures necessary to overcome the Coulomb repulsion favor photodisintegration rather than charged-particle capture. The most plausible astrophysical site is the explo- sively burning Ne/O layer in core collapse supernovae, which is heated to ignition temperatures by the outgoing shock front [3–5]. In this high-temperature environment proton-rich nuclei are produced by sequences of photo- dissociations and β + decays. In stars 20 times more mas- sive than the sun the p -process temperatures for efficient photo-disintegration are already reached at the end of hydrostatic Ne/O burning [6]. This mechanism is also called ” γ process” because proton-rich isotopes are pro- duced by ( γ, n ) reactions on pre-existing seed nuclei from FIG. 1: (Color online) Example from the chart of nuclides illustrating the position of the lightest p -nuclei, which are shielded from the s -process flow and the r -process decay chains. I. INTRODUCTION SeGLYPH<.notdef>74 SeGLYPH<.notdef>76 SeGLYPH<.notdef>75 KrGLYPH<.notdef>79 SrGLYPH<.notdef>85 KrGLYPH<.notdef>81 KrGLYPH<.notdef>82 SeGLYPH<.notdef>77 KrGLYPH<.notdef>83 SeGLYPH<.notdef>78 KrGLYPH<.notdef>84 SeGLYPH<.notdef>80 KrGLYPH<.notdef>78 BrGLYPH<.notdef>79 SeGLYPH<.notdef>82 RbGLYPH<.notdef>87 SrGLYPH<.notdef>88 SrGLYPH<.notdef>87 KrGLYPH<.notdef>86 KrGLYPH<.notdef>80 BrGLYPH<.notdef>81 SrGLYPH<.notdef>84 SrGLYPH<.notdef>86 RbGLYPH<.notdef>85 processGLYPH<.notdef>flow s- -process isotopes p r- process decayGLYPH<.notdef>chains BrGLYPH<.notdef>80 RbGLYPH<.notdef>86 KrGLYPH<.notdef>85 SeGLYPH<.notdef>81 BrGLYPH<.notdef>82 SeGLYPH<.notdef>79