Tandem Accelerator Laboratory Institute of Nuclear Physics, NCSR Demokritos Athens, Greece.

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1 Center of Excellence in Low energy Ion Beam Research and Applications p process: an experimentalist s view Sotirios V. Harissopulos Tandem Accelerator Laboratory Institute of Nuclear Physics, NCSR Demokritos Athens, Greece sharisop@inp.demokritos.gr

2 Nucleosynthesis pathways along the table of isotopes rp process powered by protons (p,γ) / β + 39 Y up to Sn Te region ρ>10 4 g/cm 3 T (1-3) 10 9 K Novae, X ray bursters 20 Ca 28 Ni Fe Si burning s and r processes powered by neutrons (n,γ) / β NeNa cycle 8 O MgAl cycle s process: (AGB stars, red giants...) τ 100 yr ρ 10 8 n/cm 3 T=( ) 10( ) 9 K pp chain CNO cycle r process:? (supernovae, ) τ 1 sec ρ n/cm 3 T =( ) 10 9 K explosive nucleosynthesis!! 2

3 Nucleosynthesis pathways along the table of isotopes - + 3

4 p nuclei solar abundances S. Galanopoulos et al., Phys. Rev. C 67, (2003) 4

5 p process nucleosynthesis M. Arnould and S. Goriely Phys. Rep. 384, 1 (2003) CONDITIONS Succession of (γ,n), (γ,p), (γ,α) reactions and partly inverse processes (n,γ), (p,γ), (α,γ) High temperatures T = K Short time scales SITES SN Explosions Pre and/or Type II SN explosion of massive stars Type Ia SN explosion of Chandrasekhar mass WDs Type Ib/Icand/or pair creation SNexplosion He detonating sub Chandrasekhar mass WDs T ρ 10 5 g/cm 3 5

6 p nuclei solar abundances (25M o ) Woosley and Howard, Ap. J. Suppl. 36, 285 (1978) S. Goriely et al., A&A 375, 35 (2001) 6

7 abundance calculations and nuclear physics input Τ ρ Μ decays, photodisintegrations, e captures, ν Ν interactions two particle fusion reactions Y i number of species i created or destroyed decay constant λ three particle reactions two successive captures with an intermediate particle unstable nucleus reaction rate: reactions / sec / cm 3 7

8 a reaction network for our sun: a pedagogical example SUN: The pp chain p(p,e + ν)d d(p,γ) 3 He I (86%) II (14%) 3 He( 3 He,2p) 4 He 3 He( 4 He,γ) 7 Be IIa ( 14%) IIb (0.02%) 7 Be(p,γ) 8 B(e +,ν) 8 Be * (α) 4 He 7 Be(e -,ν) 7 Li(p,α) 4 He 8

9 p process reaction network seed abundances (s process) reaction network p nuclei abundances (p process) reactions/sec/cm 3 HAUSER FESHBACH THEORY Optical Model Potentials Nuclear Level Densities γ Ray Strengths (32 Z 83, 36 N 131) S. Harissopulos, 5th European Summer School on Experimental Nuclear Astrophysics, Santa Tecla Catania, Sept

10 capture reactions and the Hauser Feshbachtheory Capture reactions := a special ilcase of compound nucleus (CN) reactions τ sec α + A C * (B + b) + (D + d) + α + A C * C + γ Capture reaction (via compound nucleus formation) 10

11 Input parameters entering the Hauser Feshbach calculations α + A C * (B + b) + (D + d) + := probability that α will cross the surface of A to form a compound state of C having spin J. It depends on the orbital momentum of α := probability that b escapes from a state of the compound nucleus C with spin J. := sum of probabilities over all exit channels i. If γ emission then T fromgiant Dipole de excitation excitation If particle emission then T from Optical Model Potentials (GDR) (OMP) CAUTION: When CN is excited to continuum then Ts have to be averaged Nuclear Level Density (NLD) 11

12 p nuclei solar abundances (25M o ) Uncertainties due to astrophysics models Woosley and Howard, Ap. J. Suppl. 36, 285 (1978) Uncertainties i due to nuclear physics HF (OMP, NLD, GDR, ) S. Goriely et al., A&A 375, 35 (2001) 12

13 nuclei physics uncertainties and p nuclei abundance calculations S. Goriely, ESF Workshop on p process, Vravron, Greece, 2002 & M. Arnould and S. Goriely Phys. Rep. 384, 1 (2003) Scenario: SN II explosions Scenario 1 NLDs nucleon N OMP α particle N OMP 13

14 nuclei physics uncertainties and p nuclei abundance calculations r := <συ> max. / <συ> min. for 14 different sets of nuclear ingredients (OMP, NLD, ) in HF calculations. M. Ar rnould and S. Goriely Phy ys. Rep. 384, 1 (2003) 92 Mo ncaptures pcaptures α captures P. Demetriou, C. Grama, and S. Goriely Nucl. Phys. A 707, 253 (2002) 14

15 nuclei physics uncertainties and p nuclei abundance calculations n-induced reactions p-induced reactions α-induced reactions 15

16 Gamow peaks & windows: The energies relevant to astrophysics T=1.8 T 9 T=3.3 T 9 (p,γ)reactions: E CM = 1 5 MeV, σ = 1 μb 1 mb (α,γ)reactions: E CM = 6 12 MeV, σ = μb 16

17 Capture reaction cross section measurements: Direct methods reaction to study target backing OFF BEAM activation measurements IN BEAM γ angular distribution measurements IN BEAM angle integrated measurements final nucleus must be unstable any any enriched or natural enriched min. error in σ tot := 8 10% enriched If, then If, then If, then low Z high Z mostly high Z (C, Al, ) (Ta, Au, ) (Ta, Au, ) detectors normal size HPGe (ε 30%) large volume HPGe (arrays) (ε 70%) 4π calorimeters [ large NaI(Tl) ] (ε 100%) γ rays to detect in most cases E γ 2 MeV up to E γ 15 MeV up to E γ 15 MeV 17

18 γ decay pattern of a compound nucleus E proj + E Q-value entry state unresolved excited states discrete excited states Compound Nucleus γ 0 up to 15 MeV!!! ground state 18

19 γ angular distribution IfS Stuttgart 19

20 the role of spin and parity in a compound nucleus reaction entry state spin J T J P J ENTRY J T J P TARGET : even-odd nucleus L p =0 L p =1 J TARG J ENTRY J ENTRY 1/2 0, 1 0, 1, 2 3/2 1, 2 0, 1, 2, 3 5/2 2, 3 1, 2, 3, 4 7/2 3, 4 2, 3, 4, 5 9/2 4, 5 3, 4, 5, 6 TARGET : even-even nucleus L p =0 L p =1 J TARG J ENTRY J ENTRY s=1/2 p 0 1/2 1/2, 3/2 entry state parity π(gs) * (-1) Lp = π(exc. state) TARGET CN 20

21 93 Nb(p,γ) 94 Μο 21

22 89 Y(p,γ) 90 Zr : γ angular distribution measurements 22

23 The 4π γ summing method A. Spyrou et al., PRC 76, (2007) P. Tsagari et al., PRC 70, DTL-Bochum 23

24 The 4π γ summing method A. Spyrou et al., PRC 76, (2007) P. Tsagari et al., PRC 70, DTL-Bochum 24

25 89 Y(p,γ) 90 Zr cross sections using the 4π γ summing method C o u n t s C o u n t s Segmented Demokritos 89 Y(p,γ) 90 Zr Monocrystal Univ. Bochum Photon energy (kev) F 2 F 1 GEANT sim. Y σ=(y/ε)*(1/ξ)*(a/n 2-fold A ) casc. 4-fold casc. 3-fold casc. F 0 P. Tsagari et al., PRC 70, (2004) Y 0 = F 0 / (N proj ε 0 )! Y 1 = F 1 / (N proj ε 1 ) Y 2 = F 2 /(N proj ε 2 ) 100 Y TOT = Y 0 + Y 1 + Y σ TOT = (A/N A ) (Y TOT / ξ) Ph t (k V) 25

26 The 4π γ summing method: Sum peak efficiency vs. Multiplicity in/out ratios: M=1 R = 2 M=2 R = 2 2 = 4 M=3 R = = 8 M=4 R = = 16 26

27 Sum peak efficiency check with known capture reactions 27

28 γ angular distributions vs. angle integrated measurements 28

29 typical angle integrated spectra 29

30 (p,γ) reactions : comparison with HF predictions 30

31 HF input parameters 31

32 HF input parameters 32

33 HF input parameters 33

34 HF input parameters Conclusions based on (p,γ) measurements In most cases, uncertainties affecting nuclear input (OMP, NLD) give rise to at most 40% uncertainties in the reaction rates. HF predictions are more sensitive to OMP rather than to NLD. 34

35 α OMP : (α,α) vs. (α,γ) First alarming results on 144 Sm(α,γ): Somorjai et al., A&A 333, 1112 (1998) Local OMP at 20 MeV failed at sub Coulomb energies S(Ε)= σ(ε) Ε exp(2π η(ε)) Demetriou et al, NPA 707, 253 (2002) Mohr et al. PRC 55, 1523 (1997) 35

36 MINIBALL: typical (p,γ) and (α,γ) singles spectra IKP/Cologne Mo( α,γ) 96 Ru 10 4 Yield/m mc sum peaks Count s E α =11 MeV 10 1 E( α)=9 MeV E γ (MeV) Mo( α,γ) 96 Ru E γ (kev) Co ounts Al Fe O E γ (kev) 36

37 summary : part 1 37

38 ACKNOWLEDGEMENTS Nuclear Astrophysics Group, Tandem Lab., NCSR Demokritos - Athens A. Spyrou, A. Lagoyannis, S. Galanopoulos, P. Tsagari, G. Perdikakis, T. Konstantinopoulos, M. Axiotis, Ch. Zarkadas, V. Foteinou, G. Provatas and P. Demetriou. EP3-Bochum H.W. Becker, C. Rolfs IfS-Stuttgart M. Fey, R. Kunz, J.W. Hammer GANIL : P. Ujic, F. de Oliveira, O. Sorlin, JYFL-JyväskyläJyväskylä R. Julin. P. Jones, T. Sajavara, H. Koivisto IAA-ULB S. Goriely IKP-KölnKöln A. Dewald, K.O. Zell, P. von Brentano S. V. Harissopulos, XVI Colloque GANIL, Giens, France, Sept. 6 11,