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Determination of Radiative Neutron Capture Cross Sections for Unstable Nuclei by Coulomb Dissociation

This seminar outlines the methodology and applications of the gSF method for measuring radiative neutron capture cross sections for unstable nuclei. Collaborators from various institutions present direct and indirect experimental methods, as well as the g-ray strength function method, in nuclear astrophysics research. The seminar also discusses the structure of the g-ray strength function and its application in predicting neutron capture cross sections for specific isotopes.

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Determination of Radiative Neutron Capture Cross Sections for Unstable Nuclei by Coulomb Dissociation

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  1. Determination of radiative neutron capture cross sections for unstable nuclei by Coulomb dissociation H. Utsunomiya (Konan University) Outline • Methodology of the gSF method • Applications with real photons • Applications with virtual photons RIKEN Seminar Nov. 1, 2011

  2. Collaborators H. Utsunomiyaa) , H. Akimunea) , T. Yamagataa) , H. Toyokawac) , H. Haradad), F. Kitatanid) , Y. -W. Luie) , S. Gorielyb) I. Daoutidisb) , D. P. Arteagaf) , S. Hilaireg) , and A. J. Koningh) • Department of Physics, Konan University, Japan • Institut d’Astronomie et d’Astrophysique, ULB, Belgium • c) National Institute of Advanced Industrial Science and Technology, Japan • d) Japan Atomic Energy Agency, Tokai, Naka-gun, Ibaraki 319-1195, Japan • e) Cyclotron Institute, Texas A&M University, USA • f) Institut de Physique Nucléaire, Université Paris-Sud, France • g) CEA,DAM, DIF, Arpajon, France • h) Nuclear Research and Consultancy Group, The Netherlands

  3. Radiative neutron capture cross sectionsfor unstable nuclei in nuclear astrophysics Direct measurements at CERN n-TOF, LANSCE-DANCE, Frankfurt-FRANZ and J-Parc ANNRI facilities can target some of unstable nuclei along the valley of b-stability if samples can be prepared. ---> s-process Indirect experimental method is called in for unstable nuclei along the valley of b-stability ---> s-process neutron-rich region ---> r-process surrogate reaction technique ANY OTHER?

  4. g-ray strength function method H. Utsunomiya et al., PRC80 (2009) follows the statistical model of the radiative neuron capture in the formation of a compound nucleus and its decay by using experimentally-constrained gSF. Radiative neutron capture AX(n,g)A+1X continuum E, J, p decay process gSF NLD n + AX A+1X

  5. Hauser-Feshbach model cross section for AX(n,g)A+1X Total gtransmission coefficient After integrating over J and π nuclear level density g-ray strength function X=E, M l=1, 2, … neutron resonance spacing low-lying levels source of uncertainty gSF method

  6. g-ray strength function: nuclear statistical quantity interconnecting (n,g) and (g,n) cross sectionsin the HF model calculation Radiative neutron capture Photoneutron emission continuum AX(n,g)A+1X A+1X(g,n)AX E, J, p n+AX A+1X Brink Hypothesis

  7. Structure of g-ray strength function Extra strengths Sn GDR 6 – 10 MeV PDR, M1 Primary strength E1 strength in the low- energy tail of GDR

  8. (g,g’) R. Schwengner (g,n) A. Tonchev Sn GDR CD Oslo method M. Guttormsen PDR, M1 Particle-g coin. A. Zilges (p,p’) A. Tamii P. von Neumann-Cosel

  9. Methodology of gSF method STEP 1 GDR (g,n) Measurements of (g,n) c.s. near Sn STEP 1 gSF (g,n) A-1 A Sn

  10. Methodology of gSF method STEP 2 GDR (g,n) Normalization of gSF Extrapolation of gSF by models STEP 1 gSF (g,n) A-1 A Sn Sn

  11. Methodology of gSF method STEP 2 GDR (g,n) JUSTIFICATION BY REPRODUCING KNOWN (n,g) C.S. STEP 1 gSF (g,n) A-1 A Sn Sn known (n,g)

  12. Methodology of gSF method STEP 3 GDR (g,n) neutron capture by unstable nucleus A+1X(n,g)A+2X STEP 1 STEP 2 STEP 1 STEP 2 (g,n) (g,n) A-1 A A+1 A+2 Extrapolation is made in the same way as for stable isotopes. Sn STEP 3 known (n,g) (n,g) to be deduced

  13. Applications LLFP (long lived fission products) nuclear waste Astrophysical significance Present (g,n) measurements Existing (n,g) data H. Utsunomiya et al., PRC80 (2009) (n,g) c.s. to be deduced 121 27 h 123 129 d 6 6 Sn 117 116 118 119 120 122 124 115 7 H.U. et al., PRC82 (2010) 107 6.5 106 y 3 106 108 Pd 105 104 H.U. et al., PRL100(2008) PRC81 (2010) 93 1.53 106 y 95 64 d 5 89 3.27 d Zr 94 90 91 92 96 79 2.95 103 y To be published 75 120 d Se 78 80 76 77 4

  14. Laser Compton scattering g-ray beam Inverse Compton Scattering “photon accelerator” g = Ee/mc2

  15. AIST (National Institute of Advanced Industrial Science and Technology) l=1064, 532 nm

  16. Detector System Triple-ring neutron detector 20 3He counters (4 x 8 x 8 ) embedded in polyethylene

  17. Applications LLFP (long lived fission products) nuclear waste Present (g,n) measurements Astrophysical significance STEP 1 Measurements of (g,n) cross sections STEP 2 Investigation of gSF that reproduces (g,n) cross sections Extrapolation of gSF below Sn Justification of gSF with existing (n,g) data 93 1.53 106 y 95 64 d 5 89 3.27 d Zr 94 90 91 92 96 STEP 3 Prediction of (n,g) cross sections for 93Zr and 95Zr

  18. STEP 1 – (g,n) 断面積の中性子しきい値近傍での高精度測定 91Zr 96Zr 92Zr 94Zr

  19. Application STEP 2 – Extrapolation of gSF to the low-energy region 92Zr HFB+QRPA + Giant M1 HFB+QRPA E1 strength supplemented with a giant M1 resonance in Lorentz shape Eo ~ 9 MeV, G ~ 2.5 MeV, so ~ 7 mb ~ 2% of TRK (Thomas-Reiche-Kuhn) sum rule of GDR

  20. Application STEP 2 – Justification of the adopted gSF TALYS code of the HF model

  21. Application STEP 2 – Justification of the adopted gSF

  22. Results for Zr isotopes long-lived fission product nuclear waste 93Zr[T1/2=1.5×106 y]

  23. 95Zr[T1/2=64 d] s-process branching 30-40% uncertainties

  24. Comparison with the surrogate reaction technique Forssèn et al., PRC75, 055807 (2007) Zr isotopes 93Zr(n,g)94Zr 95Zr(n,g)96Zr 1. The surrogate reaction technique gives larger cross sections by a factor of ~ 3 than the gSF method. The surrogate reaction technique gives similar cross sections to those given by the gSF method provided that a choice is made of the Lorentian type of gSF.

  25. Applications 121 27 h 123 129 d 6 6 Sn 117 116 118 119 120 122 124 115 7

  26. Sn isotopes STEP 1 Measurement of (g,n) cross sections H. Utsunomiya et al., PRC80 (2009)

  27. STEP 2 – Extrapolation of gSF to the low-energy region HFB+QRPA + PDR HFB+QRPA E1 strength supplemented with a pygmy E1 resonance in Gaussian shape Eo ~ 8.5 MeV, G ~ 2.0 MeV, so ~ 7 mb ~ 1% of TRK sum rule of GDR

  28. gSF for Sn isotopes Comparison with the Oslo method Toft et al., PRC 81 (2010) PRC 83 (2011)

  29. STEP 2– Justification of the extrapolated gSF

  30. STEP 3 – Statistical model calculations of (n,g) cross sections for radioactive nuclei Uncertainties: 30-40% 121Sn[T1/2=27 h] 123Sn[T1/2=129 d] Uncertainties: a factor of 3

  31. Applications LLFP (long lived fission products) nuclear waste Astrophysical significance 107 6.5 106 y 106 108 3 Pd 105 104

  32. STEP 1 Measurement of (g,n) cross section Pd isotopes

  33. STEP 2 – Extrapolation of gSF gSFfor 108Pd RMF + QRPA D. P. Arteaga and P. Ring, Phys. Rev. C77, 034317 (2008) Sn

  34. STEP 2 – Justification of the extrapolated gSF S. Goriely, Phys. Lett. B436, 10 (1998). Hybrid D. P. Arteaga and P. Ring, Phys. Rev. C77, 034317 (2008). Deformed RRPA

  35. long-lived fission product nuclear waste 107Pd[T1/2=6.5×106 y] 30-40% uncertainties stem from NLD

  36. 79Se(n,g)80Se 79 2.95 103 y 75 120 d Se 78 80 76 77 4 A. Makinaga et al, PRC79 (2009) Large uncertainties has remained because of a lack of justification in STEP 2. F. Kitatani (JAEA)a systematic measurement for stable Se isotopes ---> complete application of gSF method To be published

  37. s-process nucleosynthesis and stellar models Main component Weak component AGB stars（1 ≤M≤ 3 ） He-shell burning Massive stars（8 ≤ M） Core He burning Zr〜Bi Fe〜Zr 22Ne(a,n)25Mg kT=26 keV, nn≤106 cm-3 Main Weak 13C(a,n)16O kT=8 keV, nn≈107 cm-3 22Ne(a,n)25Mg kT=23 keV, nn≤1011 cm-3 Carbon burning 12C(12C,n)23Mg kT ≈ 91 keV nn≈1011 cm-3 Zr MACS s(E): E：0.3 〜 300 keV

  38. s-process branching nuclei F. Käppeler et al., Rev. Mod. Phys. 83, 157 (2011) The s-process branching is a good measure of the stellar neutron density and temperature. s-only nuclei 151Sm(n,g)@n-TOF (CERN) Sm2O3, 89.9% 151Sm, 206.4 mg

  39. s-process branching nuclei F. Käppeler et al., Rev. Mod. Phys. 83, 157 (2011) Normal applications of the gSF method with real photons requires at least 2 neighboring stable isotopes. ９ branching nuclei (g,n) (g,n) A-1 A A+1 A+2 known (n,g) (n,g) to be deduced

  40. s-process branching nuclei F. Käppeler et al., Rev. Mod. Phys. 83, 157 (2011) Some s-process branching nuclei have only one stable isotope. 8 branching nuclei stable 133Cs 159Tb 165Ho 169Tm 181Ta 203Tl branching 134,135Cs 160Tb 163Ho 170,171Tm 179Ta 204Tl

  41. s-process branching nuclei • Some s-process branching nuclei have 2 stable isotopes that are not neighboring to each other. 3 branching nuclei s-only nuclei stable 151,153Eu branching 152,154,155Eu

  42. Coulomb dissociation experiments with SAMURAI at RIKEN-RIBF 18 Coulomb dissociations 11 branching nuclei

  43. Ambitious application of the gSF method to the r-process 131Sn(n,g)132Sn cross sections in the r-process nucleosynthesis The significance is controversial！ BUT this would be the first application to a very neutron-rich nucleus. A pioneering work is in progress. 1) A systematic study of the gSF for Sn isotopes 116Sn ,…., 124Sn (7 stable) →→→ 132Sn 132Sn(g,n) data: GSI Coulomb dissociation data for 132Sn

  44. New g-ray Beam Line @ NewSUBARU

  45. Summary gSF method: (n,g) c.s. for unstable nuclei 1. Nuclear Experiment: (g,n) c.s. real photons for stable nuclei virtual photons for unstable nuclei (CD) 2. Nuclear Theory: models of gSF models of NLD primary strength: low-energy E1 of GDR extra strengths: PDR, M1 3. Coulomb dissociation experiments with SAMURAI @ RIKEN-RIBF play a key role in the application of the gSF method.

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