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## 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 

F. K¨ appeler and S. Walter Institut f¨ ur Kernphysik, Forschungszentrum Karlsruhe, Postfach 3640, D-76021 Karlsruhe, Germany 

S. Dababneh Faculty of Applied Sciences, Al-Balqa Applied University, Salt 19117, Jordan 

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. 

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 

PACS numbers: 25.40.Lw, 26.30.-k, 27.50.+e, 97.10.Cv 

## I. INTRODUCTION 

<img src='content_image/392380.jpg'>

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 

