The astrophysical p-process Zs. Fülöp ATOMKI Debrecen, Hungary 1 1

Open questions in physics 1. What is dark matter? 2. What is dark energy? 4. Do neutrinos have mass? 5. Where do ultrahigh-energy particles come from? 6. Is a new theory of light and matter needed to explain what happens at very high energies and temperatures? 7. Are there new states of matter at ultrahigh temperatures and densities? 8. Are protons unstable? 9. What is gravity? 10. Are there additional dimensions? 11. How did the Universe begin? 3. How were the heavy elements made? National Research Council Report (2003)

A chance to answer

Temperature - reaction rate Nonexplosive scenario: Low energy Small cross sections Extrapolation needed (S-factor) → indirect methods + underground labs Explosive scenario: Higher energies High cross sections Exotic nuclei (low intensities) → RIB Charged particle reaction cross sections are difficult to measure at astrophysical energies

P-process: Gamow window reachable! Low cross section → High beam current Energy range: 1-15 MeV/A High efficiency detection Background reduction Enriched (and stable) target In-beam and activation methods No extrapolation is needed Inclusive experiments Fülöp et al.: NPA758 (2005)

P-NUCLEI Heavy Proton-rich Even-even Rare (0.1-1%) Not accessible by r,s processes

Overproduction Factors High abundance: 92Mo (14.8%), 94Mo (9.25%), 96Ru (5.5%), 98Ru (1.88%)

Astrophysical p-process: an open issue Site: SNII Supernova shock passing through O-Ne layers of progenitor star (T9=1-3) Time scale: 1s Gamma-induced reactions on s-process seed nuclei: (γ,n) reaction chain → proton rich region Branching points: (γ,p) and/or (γ,α) Alternative processes e.g. ν-reactions (Fröhlich: PRL 2007) Alternative sites (Fujimoto: ApJ 2007)

Experimental charged particle rates are missing! Reaction Network T1/2=108y Experimental charged particle rates are missing!

Input Physics Stellar models Seed abundances Nuclear reaction networks: Hauser-Feshbach cross section calculations Ingredients: ground state properties, level densities, optical potentials, γ-ray strength functions… ?? The reliability of the well-known and well tested HF calculations under p-process constraints

1992: a new collaboration with Bochum Aim: experimental verification of theoretical cross sections in the mass and energy range relevant to the astrophysical p-process using the low energy accelerators of ATOMKI Masterminds: C. Rolfs, E. Somorjai Postdoc: Zs. Fulop First result: 70Ge(α,γ)74Se European Workshop on Heavy Element Nucleosynthesis. Budapest, March 9-11,1994

p-process model calculations capture cross section measurements nuclear physics input: reaction rates, etc astrophysical input: seed abundances temperature time scale, etc. p-process network calculations calculated p-isotope abundances observed p-isotope abundances

Input parameters of the statistical models masses, etc. level density optical model potential capture cross section measurements nuclear physics input: statistical model calculations Large networks Lack /too many of key reactions → Trend investigations → Global studies astrophysical input: seed abundances temperature time scale, etc. p-process network calculations calculated p-isotope abundances observed p-isotope abundances

Sensitivity studies Reaction rate sensitivity Branching point sensitivity Statistical model sensitivity on input parameters (γ,p) (γ,n) (γ,α) W.Rapp et al.: ApJ 653 (2006) T.Rauscher: PRC 73 (2006)

Mohr/Fülöp/Utsunomiya: EPJA 32 (2007) 357. Stellar enhancement 148Gd(γ,α)144Sm 144Sm(α,γ)148Gd direct: Q>0 reverse: Q<0 > Mohr/Fülöp/Utsunomiya: EPJA 32 (2007) 357. G.G. Kiss et al: PRL 101 (2008) 191101.

Experimental approaches A. Gamma induced studies (γ,n), (γ,p), (γ,α) Brehmsstrahlung γ-source + activation (Darmstadt/Dresden) Tagged γ-source + in-beam (Darmstadt) Virtual γ → Coulomb dissociation (GSI) B. Sub-Coulomb (p,γ), (p,n), (α,γ), (α,n), (α,p) + detailed balance Activation (many labs incl. ATOMKI, Notre Dame, Karslruhe) In-beam with 4π arrays: NaI (Bochum), HPGe (Köln), BaF2 (Karlsruhe) Storage ring: (p,γ) (ESR-GSI) A + B complementary, both needed for full understanding Study of different channels leading to emerging from the same nucleus Majority of published data is by activation

On-line γ-spectrometry Pros: Cons: In all cases applicable One target is enough Enriched targets Background problems Level scheme Angular distributions

70Ge(α,γ)74Se: an example Fülöp et al: Z.Phys A 355 (1996) 203.

Off-line γ-spectrometry Pros: Cons: Low background Natural target More reactions covered Limited applicability (abundance, branching, half-life, open channels) T1/2 dependent Many targets needed Beam monitoring time Nleft t1 t2 to

84,86,87Sr(p,γ)85,87,88Y: example Gy. Gyurky et al: PRC 64 (2001) 065803.

Off-line spectrum

Activation method: serious limitations Poorly known nuclear parameters (branching, T1/2) Ancillary experiments needed Too long halflife AMS: 142Nd(α,γ)146Sm (T1/2=108 y) @ANL Inadequate branching ratios (no γ-transition) Characteristic X-ray detection might help

Case study: 169Tm(α,γ/n)173/172Lu decay characteristics: G.G. Kiss et al: Phys. Lett. B 695 (2011) 419.

169Tm(α,γ)173Lu - 169Tm(α,n)172Lu LEPS detector

X-ray detection: (α,γ) possibilities at heavy mass

144Sm(α,γ)148Gd: alpha detection Si-detector underground SSNTD Eα= 3.2 MeV Somorjai et al: A&A 333 (1998) 1112.

Sensitivity for optical potentials Call for more reliable optical potentials 74Se(p,γ)75Br 144Sm(α,γ)148Gd ‘Experimental’ potential Somorjai et al.: A&A 333 (1998) 1112 Gyürky et al.: PRC 68 (2003) 055803

(α,α) experiments at low energies Experimental constraints on the optical model parameters in the A>100 region Precision scattering chamber ~100% enriched targets Experimental constraints on the optical model parameters in the A>100 region Alternative: (n,α) studies Experimental cross section Theoretical cross section Experimental Optical potential (extrapolated)

(α,α) Experiments at Low Energies

(α,α) Experiments at Low Energies

Impact on p-process network calculations 106Cd 108Cd 110Cd 108Sn 110Sn 112Sn 114Sn (,) (,n) (,p) old new secondary branches T = 2.0·109 K reaction rate Main reaction flow based on the Gyurky et al: PRC 74 (2006) 025805.

Summary p-process calculated abundances depend on HF calculations Gamow window is reachable In lack of bottleneck reaction hunt for global characteristics Stay tuned for new astrophysical models!

Outlook: the voice of NuPECC

Supported by ERC, EUROCORES ATOMKI group members: C. Bordeanu (OTKA-fellow 2010-12) J. Farkas (grad. student) Zs. Fülöp Gy. Gyürky (ERC-fellow) Z. Halász (grad. student) G.G. Kiss (postdoc) E. Somorjai T. Szücs (grad. student) Z. Korkulu & A. Ornelas (ERASMUS students 2011) In collaboration with: T. Rauscher (statistical model) I. Dillmann, R.Plag (KADoNIS) D. Galaviz/P. Mohr (elastic scattering)