The astrophysical pprocess Zs Flp ATOMKI Debrecen Hungary

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

Open questions in physics 1. What is dark matter? 2. What is dark energy? 3. How were the heavy elements made? 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? 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 Me. V/A • High efficiency detection • Background reduction • Enriched (and stable) target • In-beam and activation methods • No extrapolation is needed • Inclusive experiments Fülöp et al. : NPA 758 (2005)

P-NUCLEI • • • Heavy Proton-rich Even-even Rare (0. 1 -1%) Not accessible by r, s processes

Overproduction Factors High abundance: 92 Mo (14. 8%), 94 Mo (9. 25%), 96 Ru (5. 5%), 98 Ru (1. 88%)

Astrophysical p-process: an open issue • Site: SNII Supernova shock passing through O-Ne layers of progenitor star (T 9=1 -3) • Time scale: 1 s • 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: Ap. J 2007)

Reaction Network T 1/2=108 y 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: 70 Ge(α, γ)74 Se European Workshop on Heavy Element Nucleosynthesis. Budapest, March 9 -11, 1994

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

Input parameters of the statistical models level density capture cross section measurements astrophysical input: seed abundances temperature time scale, etc. masses, etc. nuclear physics input: statistical model calculations p-process network calculations calculated p-isotope abundances optical model potential • Large networks • Lack /too many of key reactions → Trend investigations → Global studies 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. : Ap. J 653 (2006) T. Rauscher: PRC 73 (2006)

Stellar enhancement 148 Gd(γ, α)144 Sm(α, γ)148 Gd 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: Na. I (Bochum), HPGe (Köln), Ba. F 2 (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: • In all cases applicable • One target is enough Cons: • • Enriched targets Background problems Level scheme Angular distributions

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

Off-line γ-spectrometry Cons: Pros: • Low background • Natural target • More reactions covered • Limited applicability (abundance, branching, half-life, open channels) • T 1/2 dependent • Many targets needed • Beam monitoring Nleft to t 1 t 2 time

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

Off-line spectrum

Activation method: serious limitations • Poorly known nuclear parameters (branching, T 1/2) – Ancillary experiments needed • Too long halflife – AMS: 142 Nd(α, γ)146 Sm (T 1/2=108 y) @ANL • Inadequate branching ratios (no γ-transition) Characteristic X-ray detection might help

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

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

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

144 Sm(α, γ)148 Gd: Si-detector underground Eα= 3. 2 Me. V Somorjai et al: A&A 333 (1998) 1112. alpha detection SSNTD

Sensitivity for optical potentials Call for more reliable optical potentials 144 Sm(α, γ)148 Gd 74 Se(p, γ)75 Br ‘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 106 Cd ( , n) 108 Cd Main reaction flow based on the Gyurky et al: PRC 74 (2006) 025805. ( , n) 110 Cd 114 Sn , ) ( , n) ( 112 Sn ( , p) , ) ( , n) ( 110 Sn ( , p) ( , ) ( , p) 108 Sn ( , n) T = 2. 0· 109 K ( , n) old new reaction rate secondary branches

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 Nu. PECC

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 (KADo. NIS) D. Galaviz/P. Mohr (elastic scattering)