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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 strength function in 181 Ta( ,n) 180 Ta 3. Case 2: Nuclear level density in 181 Ta( ,n) 180 Ta m 4. Case 3: M1 strength function in 91,92,94 Zr( ,n) 90,91,93 Zr 5. Summary

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

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

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

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

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

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1+1+ 9–9– 0 75 keV 180 Ta g > 1.2 x 10 15 y 8.15 h 180 Ta m mediating excited states E x > 1 MeV Incident -ray 181 Ta (Target) 181 Ta( ,n) 180 Ta 180 Ta p-process production of 180 Ta m 180 Ta gs and 180 Ta m are equilibrated under stellar condition through mediating excited states above 1 MeV. Total cross sections are needed. total

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s-process production of 180 Ta m 180 Ta 1+1+ 2+2+ 9-9- 75.3 42 0 181 Ta 7/2 + 9/2 -, 7/2 -, 5/2 - E1 T 1/2 > 1.2×10 15 y T 1/2 =8.152h 4 +, 3 + … 5 -, 4 -, 3 -, 2 - … 8+8+ 6+6+ 7-7- 5-5- (7/2 + ) T 1/2 =1.82y 179 Ta s wave neutron s wave neutron Nuclear Level Density (9 - ) = total - gs

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・ 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 S-band small linear acc. S-band small linear acc. General-purpose Storage Ring TERAS Stroge Ring NIJI-IV Pulsed slow positron beam line ・レーザーコンプトン散乱 準単色 ps-fs Ⅹ線 ・コヒーレントテラヘルツ波 AIST Electron Accelerator Facility 400MeV Electron Linear Acc. TELL ・ナノメートル～原子レベル空孔計測 Small Storage Ring NIJI-II ・ SR プロセス

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

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Laser : INAZUMA expander mirror lens Laser system

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Inverse Compton Scattering E = 1 – 40 MeV = E e /mc 2 “photon accelerator”

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

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

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

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

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

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

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

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Main ingredients in the Talys code E1 strength function Lorentzian models:Axel, PR126 (1962), Kopecky & Uhl, PRC41 (1990) HFB+QRPA model: Goriely, Khan, Samyn, NPA739 (2006) zNuclear Level density HFB+ Combinatorial model: Hilaire & Goriely, NPA779 (2006) Spin-flip giant M1 strength function by Bohr & Mottelson Global systematics in RIPL Handbook Lorentzian function : E o =41A -1/3 MeV, o = 4 MeV, f M1 =1.58 10 -9 A 0.47 MeV -3 at 7 MeV Talys code: Koning, Hilaire, Duijvestijn, Proc. Int. Conf. on Nuclear Data for Science and Technology AIP Conf. Proc. 769, 1154 (2005).

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91 Zr(n, ) 92 Zr 8 10 12 14 16 E [MeV] 92 Zr( n) 91 Zr The Lorentzian parametrization of the E1 -ray strength function for 92 Zr can fit the ( ,n) data, but strongly overestimates (n, ) cross sections. The Lorentzian parametrization of the E1 -ray strength function

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91 Zr(n, ) 92 Zr M1 strength in Zr isotopes in the photoneutron channel 91 Zr( n) 90 Zr 92 Zr( n) 91 Zr 94 Zr( n) 93 Zr M1 E1 H. Utsunomiya et al., PRL100 (2008) If we employ the HFB+QRPA E1 -ray strength function supplemented with extra M1 strength assumed at 9 MeV with σ 0 =7.5mb and =2.5 MeV in Lorentz shape, the cross sections are well reproduced. The M1 strength is about 75% larger than the strength predicted by the global systematics.

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Major shell gaps associated with spin-flip M1 excitations zZ,N=28 1f 7/2 → 1f 5/2 z 50 1g 9/2 → 1g 7/2 z 82 1h 11/2 → 1h 9/2 z 126 1i 13/2 → 1i 11/2

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1g 9/2 1g 7/2 2d 5/2 50 J = 5/2 + for 91,93 Zr gs means that excess neutrons occupy the 2d 5/2 shell. Spin-flip M1 M1 strength can be similar for 91,92,94 Zr.

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o =7.5mb, =2.5 MeV E o =9 MeV Lorentz shape 92 Zr 94 Zr 91 Zr

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Medium-range plan 1: E1, M1 -ray strength functions zSystematic measurements of ( ,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) H. Utsunomiya et al., PRL100 (2008)

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Partial cross section for Isomers and total cross sections 5. 196 Pt( ,n) 195 Pt m (13/2 +, 259.30 keV, 4.02d) 6. 187 Re( ,n) 186 Re m ((8 + ), 149 keV, 2.0x10 5 y) 187 Re( ,n) 186 Re gs (1 -, 90.64h) 7. 178 Hf( ,n) 177 Hf m (37/2 -, 2740.0 keV, 51.4m) 8. 176 Lu( , ’) 176 Lu m (1 -, 123.0 keV, 3.64h) Medium-range plan 2: Level densities S. Goko et al., PRL96 (2006)

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Summary The SF 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 SF and NLD of direct relevance to the p-, s-, and r-process nucleosynthesis of heavy elements.

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