1 / 28

Photodisintegration and nuclear statistical quantities in astrophysics

Photodisintegration and nuclear statistical quantities in astrophysics. H. Utsunomiya (Konan University). SNP2008, Ohio University, July 8-11, 2008. Outline 1. Photodisintegration and nuclear statistical quantities 2. Case 1: E1 g strength function in 181 Ta( g ,n) 180 Ta

avidan
Download Presentation

Photodisintegration and nuclear statistical quantities in astrophysics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Photodisintegration and nuclear statistical quantities in astrophysics H. Utsunomiya (Konan University) SNP2008, Ohio University, July 8-11, 2008 Outline 1. Photodisintegration and nuclear statistical quantities 2. Case 1: E1 g strength function in 181Ta(g,n)180Ta 3. Case 2: Nuclear level density in 181Ta(g,n)180Tam 4. Case 3: M1 g strength function in 91,92,94Zr(g,n) 90,91,93Zr 5. Summary

  2. Collaborators Konan U.H. Utsunomiya,T. Yamagata, H. Akimune AISTH. Toyokawa, T. Matsumoto, H. Harano JAEA H. Harada, S. Goko RCNPT. Shima NewSUBARU S. Miyamoto Texas A&M, USAY.-W. Lui ULB, Brussels, Belgium S. Goriely CEA-Bruyères-le-Châtel, France S. Hilaire ZG Petten, The NetherlandsA.J. Koning

  3. What can we do with real photons? • Photonuclear reactions are an excellent electromagnetic probe. • The universal role of photonucelar reactions is to investigate the g strength function and nuclear level density that are key nuclear ingredients for the p-, s-, and r-process. s-process Nucleosynthesis of heavy elements through gSF and NLD ・p-process ・s-process ・r-process p-process r-process Nucleosynthesis of light elements by the detailed balance

  4. Nuclear Statistical Quantities in the Hauser-Feshbach model Common to Radiative Capture and Photodisintegration A(x, g)B (x=n, p, d, t, 3He, a) Optical potential Level density continuum Mass, deformation A + x g-ray strength function Discrete levels Ex, Jp RIPL Handbook/IAEA-TECDOC http://www-nds.iaea.org/ripl/ B

  5. Photoreaction rates for nuclei in state m Neutron channel (g,n) sn(E) GDR Brink hypothesis GDR is built on excited states. (g,n) (n,g) Gamow peak Sn Ex Key issues (Z, A-1) ・E1, M1 g strength functions above and below Sn ・Nuclear level densities ng(E,T) (g,g’) Planck Distr. (Z,A)

  6. Origin of 180Tam Only naturally occurring isomer and nature’s rarest nuclide p process 180W 181W 182W 183W s process 180m 179Ta 181Ta 182Ta 180g 180m 176Hf 177Hf 178Hf 179Hf 181Hf 180g s process r process

  7. 181Ta(g,n)180Ta Incident g-ray 181Ta (Target) p-process production of 180Tam 180Tags and 180Tam are equilibrated under stellar condition through mediating excited states above 1 MeV. Total cross sections are needed. stotal mediating excited states Ex > 1 MeV 180Tam > 1.2 x 1015 y 75 keV 9– 180Tag 0 8.15 h 1+ 180Ta

  8. 9/2-, 7/2-, 5/2- 4+, 3+ 5-, 4-, 3-, 2- … … 5- (7/2+) E1 s-process production of 180Tam s wave neutron s wave neutron 179Ta T1/2=1.82y 6+ Nuclear Level Density 7- s(9-) = stotal - sgs 8+ T1/2 > 1.2×1015y 9- 75.3 2+ 42 T1/2=8.152h 1+ 0 180Ta 7/2+ 181Ta

  9. AIST Electron Accelerator Facility Stroge Ring NIJI-IV General-purpose Storage Ring TERAS ・VUV-IR自由電子レーザー ・レーザー逆コンプトン光 ・偏光アンジュレータ光 ・放射光 400MeVElectron Linear Acc. TELL S-band small linear acc. ・レーザーコンプトン散乱 　　　　　　準単色ps-fsⅩ線 ・コヒーレントテラヘルツ波 Small Storage RingNIJI-II ・SRプロセス Pulsed slow positron beam line ・ナノメートル～原子レベル空孔計測

  10. Tsukuba Electron Ring for Acceleration and Storage (TERAS) l=532 nm 2.4 eV

  11. Laser system mirror expander lens mirror Laser : INAZUMA

  12. Eg = 1 – 40 MeV Inverse Compton Scattering “photon accelerator” g = Ee/mc2

  13. Neutron Detector System Triple-ring neutron detector 20 3He counters (4 x 8 x 8 ) embedded in polyethylene triple ring detectors Monitor: NaI(Tl)

  14. Target Sample；181Ta 3He Proportional Counter ×20 NaI(Tl) Scintillator Target Sample；197Au Neutron Moderator ; Polyethylene Experimental Set-up for direct neutron detection and photoactivation

  15. 181Ta(g,n)180Ta :stotal Utsunomiya et al., PRC(2003) Extra E1 g-ray strength near Sn

  16. Experimental results, and comparison with theoretical models Goko et al. Phys. Rev. Lett. 96, 192501 (2006) Systematic uncertainties 10～26% Combinatorial NLD model Present work (2006) Hilaire & Goriely, NPA779 (2006) IAEA : Lee et al. (1998) Statistical NLD model

  17. Goko et al. Phys. Rev. Lett. 96, 192501 (2006) for the s-process production of 180Tam Present results at 30 keV 0.04 30keV (s-process) Combinatorial NLD model Statistical NLD model Previous Predictions 44mb (Zs. Nèmeth, F.Käppeler, G.Reffo ;1992) sm： sm/stot： 0.02～0.09 (K.Yokoi, K.Takahashi ;1983) 0.043±0.008 (Zs. Nèmeth, F.Käppeler, G.Reffo ;1992)

  18. M1 strength in Zr isotopes (p,p’): giantM1 resonance M1 GDR Crawley et al., PRC26, 87 (1982) Sn Nanda et al., PRL51 (1982) E1 Anantaraman et al., PRL46 (1981) Bertrand et al., PL103B (1981) M1 E1 Strong M1 strength of giant-resonance type was observed in (p,p’) below GRD. The M1 strength lies over the neutron separation energy for 92,94,96Zr. Sn M1 E1 Sn (g,g’): giantM1 resonance M1 E1 Laszewski et al., PRL59 (1987) (e,e’) weak & fragmented Sn Meuer et al., NPA 1980 Excitation Energy

  19. (g,n) cross sections on Zr isotopes 91Zr(g,n)90Zr Threshold behavior of (g,n) cross sections is given by 92Zr(g,n)91Zr In the E1 photo-excitation, is allowed. However, the experimental cross sections are strongly enhanced from the expected behavior. 94Zr(g,n)93Zr The generalized Lorentzian parametrization of the E1 g-ray strength function significantly underestimates the cross sections .

  20. Main ingredients in the Talys code Talys code: Koning, Hilaire, Duijvestijn, Proc. Int. Conf. on Nuclear Data for Science and Technology AIP Conf. Proc. 769, 1154 (2005). • E1 g strength function Lorentzian models:Axel, PR126 (1962), Kopecky & Uhl, PRC41 (1990) HFB+QRPA model: Goriely, Khan, Samyn, NPA739 (2006) • Nuclear Level density HFB+ Combinatorial model: Hilaire & Goriely, NPA779 (2006) • Spin-flip giant M1 g strength function by Bohr & Mottelson Global systematics in RIPL Handbook Lorentzian function : Eo=41A-1/3 MeV, Go= 4 MeV, fM1=1.58 10-9 A0.47 MeV-3 at 7 MeV

  21. The Lorentzian parametrization of the E1 g-ray strength function 92Zr(g,n)91Zr 91Zr(n,g)92Zr • 10 12 14 16 • E [MeV] The Lorentzian parametrization of the E1 g-ray strength function for 92Zr can fit the (g,n) data, but strongly overestimates (n,g) cross sections.

  22. M1 strength in Zr isotopes in the photoneutron channel H. Utsunomiya et al., PRL100 (2008) 91Zr(g,n)90Zr 91Zr(n,g)92Zr M1 E1 92Zr(g,n)91Zr M1 E1 If we employ the HFB+QRPA E1 g-ray strength function supplemented with extra M1 strength assumed at 9 MeVwith σ0=7.5mb and G=2.5 MeV in Lorentz shape, the cross sections are well reproduced. 94Zr(g,n)93Zr M1 E1 The M1 strength is about 75% larger than the strength predicted by the global systematics.

  23. Major shell gaps associated with spin-flip M1 excitations • Z,N=28 1f7/2→　1f5/2 • 50 1g9/2→ 1g7/2 • 82 1h11/2→ 1h9/2 • 126 1i13/2→ 1i11/2

  24. 1g7/2 M1 strength can be similar for 91,92,94Zr. Spin-flip M1 Jp= 5/2+ for 91,93Zrgs means that excess neutrons occupy the 2d5/2 shell. 2d5/2 1g9/2 50

  25. 92Zr Lorentz shape 94Zr 91Zr so=7.5mb, G=2.5 MeV Eo=9 MeV

  26. Medium-range plan 1: E1, M1 g-ray strength functions H. Utsunomiya et al., PRL100 (2008) • Systematic measurements of (g,n) cross sections for as many stable nuclei as possible around the magic numbers 50, 82 and 126 1. Zr isotopes (Zr-90,91,92,94,96) 2. Mo isotopes (Mo-92,94,95,96,97,98,100) 3. Sn isotopes (Sn-116,117, Sn-118,119,120,122,124) 4. Nd isotopes (Nd-142,143,144,145,146,148,150) 5. Pb isotopes (Pd-206,207,208)

  27. Medium-range plan 2: Level densities S. Goko et al., PRL96 (2006) Partial cross section for Isomers and total cross sections 5. 196Pt(g,n)195Ptm(13/2+, 259.30 keV, 4.02d) 6. 187Re(g,n)186Rem((8+),149 keV, 2.0x105y) 187Re(g,n)186Regs(1-, 90.64h) 7. 178Hf(g,n)177Hfm(37/2-, 2740.0 keV, 51.4m) 8. 176Lu(g,g’)176Lum(1-, 123.0 keV, 3.64h)

  28. Summary • The gSF and NLD are key nuclear statistical quantities in the Hauser-Feshbach model calculations of neutron capture and photoreaction rates in nuclear astrophysics. • Photonuclear reactions are an excellent electromagnetic probe of gSF and NLD of direct relevance to the p-, s-, and r-process nucleosynthesis of heavy elements.

More Related