Cross section measurements of proton capture reactions on Sr isotopes for astrophysical applications

S. Harissopulos, E. Vagena, M. Axiotis, S. Galanopoulos, V. Foteinou, A. Lagoyannis and P. D e m e t r i o u (accepted for publication at PRC) Why there is a need for extensive study of the proton-capture reaction cross sections?

Why Sr? Why there is a need for extensive study of the proton-capture reaction cross sections?

• A combination of the (γ,p), (γ,n), (γ,α) and (p,γ), (n,γ), (α,γ) reactions forms the p-process. • p-process is responsible for the production of 35 neutron-deficient stable nuclei heavier than Fe, the so-called p-nuclei. • p-nuclei expands from Z=34 (Se) to Z=80 (Hg). • Their basic characteristic its their scarcity (very low isotopic abundance). • The seed nuclei (progenitors) needed for this process to occur are formed from the s-process (slow neutron capture reactions). p-process

evolution of the p-process during a shock wave propagation through an oxygen-neon burning layer of a 25 solar mass type II Supernova Interior Structure of a Massive Star

Anna Simon, Un.Notre Dame p-process

To understand the p-process we require information on the:

• stellar environment (density, temperature of the zone) • nuclear physics (nuclear masses, half-lives of the unstable nuclei and reaction rates of all the reactions ~ 20000 reactions

Cross sections rely on models (Hauser-Feshbach statistical model)

From the BUT !! ~ 200 stable nuclei ~ 30 datasets in the To verify the HF model energy region of (new) experimental data is needed! astrophysical interest Why Sr?

• Sr has a p-nuclei (84Sr) • The new data complements a previous work by Galanopoulos et. al, 2003 • Complete the systematic study at the region from Se to Mo (yellow boxes-measurements performed by Harissopoulos, Foteinou, Axiotis, Lagogiannis, Spyrou et al.) Experiments

• γ-angular distributions: 4 MV single-stage Dynamitron accelerator, University of Stuttgart, Germany • 4π γ-summing: Dynamitron-Tandem-Laboratorium (DTL), Ruhr-Universitat, Bochum, Germany

properties of the Sr targets Theoretical modeling

• The theoretical results were calculated using the TALYS 1.95 code. • Input: Optical potentials (microscopic JLM potential), Nuclear Level densities and γ-ray strength function models

Model combination Nuclear Level densities γ-ray strength function abbreviation model models TALYS-2 HFBCS HFBCS/QRPA TALYS-3 HFB HFB/QRPA TALYS-4 HFB/T HFB/T TALYS-5 HFB/T RMF/T TALYS-6 HFB D1M/HFB/QRPA TALYS-7 HFB HG TALYS-8 HFBCS HG TALYS-0 (KD OMP) -default CTFG KU Constraining the JLM/B pOMP against the experimental data

The general functional form of the Lane-consistent JLM/B OMP is given by

isoscalar isovector spin-orbit interaction

Ranged the λV,W : the normalization parameters for the real, imaginary, isoscalar components Results: 88Sr(p,γ)89Y Comparison of the experimental astrophysical S factors with calculations

The best combination was found to be TALYS-2

with fv=1.1, fw=1 Results: 87Sr(p,γ)88Y Comparison of the experimental astrophysical S factors with calculations

The best combination was found to be TALYS-2

with fv=1, fw=1 Results: 86Sr(p,γ)87Y Comparison of the experimental astrophysical S factors with calculations

The best combination was found to be TALYS-5

with fv=1.1, fw=1 Conclusions

• 86Sr, 87Sr and 88Sr isotopes were determined at energies relevant to p- process nucleosynthesis from γ-angular distribution measurements and angle-integrated γ spectra taken with the 4π γ-summing technique.

• A good agreement was found between our data and the TALYS calculations, obtained using the phenomenological nucleon–nucleus OMP of Koning and Delaroche and the constrained JLM model for specific combinations. Cross section measurements of proton capture reactions on Sn isotopes for astrophysical applications

In progress

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Ec.m. (MeV) Systematics of semi-microscopic proton-nucleus optical potential at low energies relevant to nuclear astrophysics

E.Vagena, M.Axiotis, P. D e m e t r i o u (accepted for publication at PRC)