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Title. V.A. Chetvertkova , B.S. Ishkhanov, V.N. Orlin, V .V. Varlamov Skobeltsyn Institute of Nuclear Physics and Physics Faculty, Lomonosov Moscow State University, 119991 Moscow, Russia EXPERIMENTAL-THEORETICAL EVALUATION OF PARTIAL PHOTONEUTRON REACTIONS  (  ,n) AND  (  ,2n)

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  1. Title V.A. Chetvertkova, B.S. Ishkhanov, V.N. Orlin,V.V. Varlamov Skobeltsyn Institute of Nuclear Physics and Physics Faculty, Lomonosov Moscow State University, 119991 Moscow, Russia EXPERIMENTAL-THEORETICAL EVALUATION OF PARTIAL PHOTONEUTRON REACTIONS (,n) AND (,2n) CROSS SECTIONS FOR Sn ISOTOPES V.Varlamov, EMIN-2009 (21 – 26 September)

  2. n-2n-3n Giant Dipole Resonance (for example, 119Sn) • Balance of cross sections of reactions with several (primarily 1 and 2) outgoing neutrons is very important characteristic of nucleus photodisintegration process: • competition of various decay channels; • competition of direct and statistical processes; • effects of GDR configurational splitting; • effects of GDR isospin splitting; • ….many others. (,abs) = (,n) + (,2n) + (,3n) +…+ (,p) + … + (,f) = (,sn) + (,p) + … + (,f) (,xn) = (,n) + 2(,2n) + 3(,3n) +… V.Varlamov, EMIN-2009 (21 – 26 September)

  3. Thresholds Energy thresholds of various reactios are close to each other, moreover for 112,114,116Sn Bp < Bn (Bnp < B2n) (,xn) = (,n) + 2(,2n) + …+ (,np) + (,n2p) + 2(,2np) + ...  (,nX) + 2(,2nX) + ... V.Varlamov, EMIN-2009 (21 – 26 September)

  4. Disagreements Bremsstrahlung experiments: where (E) is cross section of reaction (,xn) with threshold Eth at photon energy E; W(Em,E) is bremsstrahlung spectrum with end-poin energy Em;  is normalization constant. (,nX) contribution into (,xn) determined using statistical theory. Quasimonoenergetical annihilation photons experiments - 3 steps: 1) measurement of yield Ye+(Ej) resulted from sum of photons from positron annihilation and bremsstrahlung; 2) measurement of yield Ye-(Ej) resulted from electron bremsstrahlung; 3) (E)Ye+(Ej) - Ye-(Ej) = Y(Ej) . Majority of data - Livermore (USA) and Saclay (France) - different methods of neutrons outgoing from reactions (,nX) and (,2nX) multiplicity sorting. Significant systematical disagreemrnts! V.Varlamov, EMIN-2009 (21 – 26 September)

  5. 120Sn-n-2n – Livermore QMA-data: close to evaluated ones 120Sn(,nX) – evaluated - data (will be explained further) – Moscow BRA- data: scattered around evaluated ones 120Sn(,2nX) – Saclay QMA-data: far from evaluated ones V.Varlamov, EMIN-2009 (21 – 26 September)

  6. “(,nX) – (,2nX)” – Fig. Graphical presentation of (,nX) – (,2nX) disagreements between Saclay and Livermore data Squares - - ratios for (,nX) reactions – are larger than 1.0 Triangles -  - ratios for (,2nX) reactions – are smaller than 1.0. 51V, 75As, 89Y, 90Zr, 115In, 116,117,118,120,124Sn, 127I, 133Cs, 159Tb, 165Ho, 181Ta, 197Au, 208Pb, 232Th, 238U V.Varlamov, EMIN-2009 (21 – 26 September)

  7. Table < 1 > 1 Clear systematical Saclay/Livermore disagreements V.Varlamov, EMIN-2009 (21 – 26 September)

  8. “n-2n” correction formulae Total photoneutron reaction cross section in GDR energy region (,xn) = (,nX) + 2(,2nX). Ratio R (“Saclay/Livermore” normalization) for all reactions cross sections R= xnS/xnL = nS/nL = 2nS/2nL = (nS + 22nS)/(nL + 22nL), xnS = (nS + 22nS) = RxnL = R(nL + 22nL) . Saclay corrected 2nS* must be equal to Livermore corrected: 2nL* = R2nL, therefore: 2nL* = 2nS* = R2nL = 2nS + 1/2(nS - RnL) . Saclay (,n) reaction cross section part 1/2(nS - RnL) is “transmitted back” to Saclay (,2n) reaction cross section 2nS. V.Varlamov, EMIN-2009 (21 – 26 September)

  9. 116,118,120Sn 116Sn 120Sn 118Sn Part of Saclay (,nX) reaction cross section transported back into (,2nX) cross section Corrected Saclay (,nX) reaction cross section – error bars (line – uncorrected data). (,nX) (,2nX) In principle that’s possible to put Saclay’s data into consistency with Livermore’sones using correction of multiplicity sorting V.Varlamov, EMIN-2009 (21 – 26 September)

  10. 116Sn-n 116Sn Definite multiplicity sorting errors 0 Livermore data for (,nX): negative cross section values, very strange bump at higher energies V.Varlamov, EMIN-2009 (21 – 26 September)

  11. Summary • Short summary: • there are a lot of data for partial photoneutron reaction cross section data; • significant systematical disagreements were found out; • many different methods were used, all of them have definite shortcomings; • an unuque treatment is needed. V.Varlamov, EMIN-2009 (21 – 26 September)

  12. New treatment • New experimental-theoretical treatment • of the evaluation of • partial photoneutron reactions (,nX) and (,2nX) cross sections: • initial data - experimental exp(,xn) reaction cross sections that are free of shortcomings of meatods of neutron multiplicity sorting; • separation of partial cross sections using theoretically calculated • transitional function of multiplicity • Ftheor= theor(,2nX) / theor(,xn) = • theor(,2nX) / [theor(,nX) + 2theor(,2nX)] • eval(,2nX) = Ftheorexp(,xn) • eval(,nX) = (1 - 2Ftheor)exp(,xn) V.Varlamov, EMIN-2009 (21 – 26 September)

  13. Model • Model • (B.S.Ishkhanov, V.N.Orlin. Physics of Particles and Nuclei 38, 232 (2007), • Physics of Atomic Nuclei 71, 493 (2008)): • semiclassical exitonpreequilibrium model of photonuclear reaction based on the Fermi gas densities; • effects of nucleus deformation; • effects of Giant Dipole Resonance isospin splitting. • M.B. Chadwick et al., Phys. Rev. C 44, 814 (1991). V.Varlamov, EMIN-2009 (21 – 26 September)

  14. Competition Various decay channels competition 124Sn (,0pkn) (,1pkn) (,2pkn) V.Varlamov, EMIN-2009 (21 – 26 September)

  15. F Ftheor= theor(,2nX) / [theor(,nX) + 2theor(,2nX)], arb. units 0.5 • Main features: • threshold behavior; • 0.5 limit for absolue value - that is division of (,2nX) to itself twised (with small addition of (,nX)); • weak decrease at B3n because of (,3n) contribution B3n tresholds of (,3n) reactions E, MeV V.Varlamov, EMIN-2009 (21 – 26 September)

  16. 116Sn-n 116Sn There are definite discrepancies in neutron multiplicity sorting. Definite multiplicity sorting errors 0.5 0  B2n  B3n (,2nX) F  __________________ < 0.5 (,nX) + 2 (,2nX) Livermore data for (,nX): negative cross section values and strange bump at high energies - neutron multiplicity sorting effects V.Varlamov, EMIN-2009 (21 – 26 September)

  17. 120,124Sn There are definite discrepancies in neutron multiplicity sorting 120Sn 124Sn  B2n  B2n  B3n  B3n This situation is near normal This situation is not normal V.Varlamov, EMIN-2009 (21 – 26 September)

  18. Eval-data • (,nX) and (,2nX) experimental-theoretical evaluation: • calculation of theoretical cross sectionstheor(,nX) and theor(,2nX); • calculation of theoretical sum cross sectiontheor(,xn) = theor(,nX) + 2theor(,2nX); • calculation of theoretical transition multiplicity function • Ftheor= theor(,2nX) / theor(,xn) = theor(,2nX) / [theor(,nX) + 2theor(,2nX)]; • evaluation of partial reaction cross sections • eval(,2nX) = Ftheorexp(,xn) and • eval(,nX) = (1 - 2Ftheor)exp(,xn) • for each individual experiment; • joint evaluation • summation eval-joint(,sn) = eval-joint(,nX) + eval-joint(,2nX) (,abs). V.Varlamov, EMIN-2009 (21 – 26 September)

  19. Agreements 116Sn 117Sn 124Sn In general there are agreements between data obtained by 4 different ways: 1) bremsstrahlung photons and statistical theory; 2) quasimonoenergetical photons and neutron multiplicity sorting method of Livermore; 3) quasimonoenergetical photons and neutron multiplicity sorting method of Saclay; 4) new experimental-theoretical evaluation. V.Varlamov, EMIN-2009 (21 – 26 September)

  20. Disagreements - Saclay eval(,nX) In detailes: clear disagreements were revealed for energies higher B2n for Saclay multiplicity sorting data for 3 isotopes 116Sn 118Sn 120Sn eval(,2nX) V.Varlamov, EMIN-2009 (21 – 26 September)

  21. Disagreements - 116Sn eval(,nX) F increasing -> (,nX) decreasing 116Sn eval(,2nX) F decreasing -> (,nX) increasing In detailes: clear disagreements were revealed for energies higher B2n for Livermore multiplicity sorting data for 116Sn V.Varlamov, EMIN-2009 (21 – 26 September)

  22. Disagreements - 124Sn In detailes: clear disagreements were revealed for energies higher B2n for Livermore multiplicity sorting data for 124Sn eval(,nX) F decreasing -> (,nX) increasing 124Sn eval(,2nX) F decreasing -> (,2nX) decreasing V.Varlamov, EMIN-2009 (21 – 26 September)

  23. Disagreements - BR In detailes: disagreements were revealed for energies higher B2n for data obtained using bremsstrahlung for 114,116,117,119Sn. Maybe that is the result of large direct processes contributions into the GDR B.L. Berman, S.S. Fultz. Measurements of the Giant Dipole Resonance with Monoenergetic Photons. Rev. Mod. Phys. 1975. V. 47. P. 713: that is for 117Sn V.Varlamov, EMIN-2009 (21 – 26 September)

  24. Important results So: 1) proposed experimental-theoretical evaluation gives results that are generalally in agreement with experimental data; 2) evaluated data are in good agreement with data obtained using bremsstrahlung and using qiasimonoenergetical photons at Livermore; 3) evaluated data are not in good agreement with data obtained at Saclay; 4) each case of clear disagreements can be explained by definite shortcomings of neutron multiplicity sorting procedures used; 5) therefore evaluated data could be interpreted as free of shortomings discussed. V.Varlamov, EMIN-2009 (21 – 26 September)

  25. (,nX) - (,2nX) Clear smooth behavior of both partial reactions cross sections with A changing (,nX) is decreasing, but (,2nX) is increasing because (Em – B2n) decreasing. V.Varlamov, EMIN-2009 (21 – 26 September)

  26. Main param. Main GDR parameters comparison for (,sn) (,abs): good agreement in energy position, absolute value and shape • Main A-dependencies • (112  124): • Em shifts to smaller values; •  shifts to smallr values • (till magic number N = 82). • m is about constant. V.Varlamov, EMIN-2009 (21 – 26 September)

  27. Integr. cross sect. Integrated cross sections comparison for (,sn) (,abs) GDR ((,sn) (,abs)) integrated cross section is practically constant in 112Sn124Sn. V.Varlamov, EMIN-2009 (21 – 26 September)

  28. Summary Summary Partial photoneutron reactions cross sections (,nX) and (,2nX) data for 112,114,116,117,118,119,120,122,124Sn isotopes were systematically analysed. Clear systematical disagreements between data obtained using various experimental methods were revealed and interpreted as results of shortcomings of neutron multiplicity sorting procedures. The experimental-theoretical method free from neutron multiplicity sorting problems was proposed using experimental data only for total neutron yield reaction cross section exp(,xn) = exp(,nX) + 2exp(,2nX). Contributions of partial reaction cross sections into total one was evaluated using the theoretically calculated transitional multiplicity function Ftheor= theor(,2nX) / theor(,xn): eval(,2nX) = Ftheor exp(,xn) eval(,nX) = (1 - 2 Ftheor)exp(,xn). In general good agreement was obtained between evaluated data and experimental ones with the exception of several cases of Saclay data. Using jointly evaluated partial reaction cross sections eval(,2nX) and eval(,nX) total eval(,sn) = eval(,nX) + eval(,2nX)  (,abs) was obtained and analysed for all 9 Sn isotopes. V.Varlamov, EMIN-2009 (21 – 26 September)

  29. Thanks THANKS A LOT FOR ATTENTION ! EXPERIMENTAL-THEORETICAL EVALUATION OF PARTIAL PHOTONEUTRON REACTIONS (,n) AND (,2n) CROSS SECTIONS FOR Sn ISOTOPES V.Varlamov, EMIN-2009 (21 – 26 September)

  30. Theory Theory Semiclassical exitonpreequilibrium model of photonuclear reaction based on the Fermi gas densities and taking into account the effects of nucleus deformation and of GDR isospin splitting. Bohr description of (,lpkn): i -one of 4 components (2 isospins - T0 and T0 + 1 and 2 directions of vibration), GDR - Lorenz lines with W - decay probabilities (recurrent): where V.Varlamov, EMIN-2009 (21 – 26 September)

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