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

2. 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)

3. A chance to answer

4. 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

5. 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)

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

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

8. 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)

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

10. 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

11. 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

13. 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

14. 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

15. 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)

16. 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)

17. 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

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

19. 70Ge(α,γ)74Se: an example
Fülöp et al: Z.Phys A 355 (1996) 203.

20. 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

21. 84,86,87Sr(p,γ)85,87,88Y: example
Gy. Gyurky et al: PRC 64 (2001)

22. Off-line spectrum

23. 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

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

25. 169Tm(α,γ)173Lu - 169Tm(α,n)172Lu
LEPS detector

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

27. 144Sm(α,γ)148Gd: alpha detection
Si-detector underground
SSNTD
Eα= 3.2 MeV
Somorjai et al: A&A 333 (1998) 1112.

28. 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)

29. (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)

30. (α,α) Experiments at Low Energies

31. (α,α) Experiments at Low Energies

32. 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)

33. 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!

34. Outlook: the voice of NuPECC

35. Supported by ERC, EUROCORES
ATOMKI group members:
C. Bordeanu (OTKA-fellow )
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)