Evaluation of partial and total photoneutron reactions cross sections using new objective physical data reliability criteria

Varlamov, V.V.

Автор: Varlamov V.V.
Сборник: 2nd Research coordination meeting updating photonuclear data library and generating a reference database for photon strength functions, 16 – 20 October 2017, IAEA Headquarters, Vienna, INDC International Nuclear Data Committee Summary Report
Серия: INDC(NDS)-0745
Год издания: 2018
Место издания: IAEA NDS Vienna, Austria
Первая страница: 4
Последняя страница: 6
Аннотация: The following ratios have been proposed as objective physical criteria of partial photoneutron reaction cross section data reliability, Fi = SIG(g,in)/SIG(g,Sn) (1) where σ(γ, in) are the definite partial reaction cross sections, with i = 1 for (γ, 1n) reaction, i = 2 for (γ, 2n) reaction, etc., and σ(γ, Sn) is the neutron yield cross section, SIG(g,Sn) = SIG(g,1n) + 2SIG(g,2n) + 3SIG(g,3n) + … (2) According to the definition, F1 cannot exceed the value 1.00, similarly F2 cannot exceed the value of 0.50, F3 the value of 0.33, etc. Larger Fiexp values will lead to an incorrect (physically unreliable) determination of the corresponding σexp(γ,in). Because all the terms in the Fi ratios are cross sections, negative values of these ratios are simply incorrect and due to the use of incorrect cross-section data. A combined experimental-theoretical method for the evaluation of partial reaction cross sections using data reliability criteria has been developed. It is based on using the experimental value σexp(γ,Sn), is rather independent of the problem regarding the neutron multiplicity sorting because all detected neutrons are included, and the correction functions Ftheor calculated using the Combined Model of Photonuclear Reactions (CMPNR): SIGeval(g, in) = FithSIGexp(g, Sn) = [SIGth(g, in)/SIGth(g, Sn)]SIGexp(g, Sn). (3) It was shown also that the partial reaction cross sections evaluated by using Fitheor in accordance with eq. (3) for 181Ta, 197Au and 209Bi nuclei agree with the corresponding experimental results obtained by using the activation method. So if Fiexp noticeably differ from Fitheor one has definite doubts in experimental data reliability. 1. Programme of work under the Contract • evaluations of cross sections for partial photoneutron reactions (g, 1n), (g, 2n), and (g, 3n) and also the total photoneutron reaction [(g, 1n) + (g, 2n) + (g, 3n)] will be performed using objective physical criteria of data reliability and experimental-theoretical method; • evaluations will be performed first of all for nuclides which are not available in the existing IAEA Photonuclear Data Library (Se, Y, Rh, In, Ba, La, Ce, Ho) and for nuclei for which there are issues of reliability (Cu, As, Sn, Cs, Ba, Pr, Ho, W, Nd, Gd, Au); • evaluated cross sections will be compared with the results of new measurements that will be carried out using new facilities and various methods at MSU SINP (Russia) and in collaborations with Konan University (NewSubary, Japan) and Extreme Light Infrastructure – Nuclear Physics (ELI-NP, Romania); • neutron emission spectra will be calculated using the Combined Model of Photonuclear Reactions (CMPNR) for some of above-mentioned nuclei as well as for many nuclei already investigated (Sn, La, Ta, Tb, Au, Pb, Bi, etc.) and analyzed; • corresponding ENDF format files for including into the IAEA Photonuclear Data Library will be produced. 1. The 1st CRP year 2.1. The working plan The working plan for the first year was the following: 1) In addition to many nuclei investigated before (for example 91,94Zr, 115In, 116Sn, 159Tb, 181Ta, 208Pb) for 9 new nuclei (63,65Cu, 80Se, 89Y, 133Cs, 138Ba, 141Pr, 165Ho, 186W) energy dependencies of multiplicity transitional functions Fiexp will be obtained from experimental data in the energy range of the Giant Dipole Resonance (GDR). 2) For nuclei mentioned theoretical functions Fitheor will be calculated (CMPNR). 3) The analysis of experimental partial reactions cross sections will be carried out using reliability criteria. 4) For all 9 nuclei mentioned above the evaluated cross sections for partial reactions (g,n), (g,2n), and (g,3n) and also total photoneutron reaction (SIG,tot) = (g,n) + (g,2n) + (g,3n) will be obtained for energies of GDR by experimentally-theoretical method. 5) For all 9 nuclei integrated cross sections will be calculated for various photon energy regions. 6) For selected nuclei (181Ta, 208Pb, 209Bi, etc.) neutron emission spectra will be calculated in the frame of the CMPNR. 2.2. The results obtained In accordance with the working plan the experimental data for partial photoneutron reaction cross sections were analyzed using objective physical data reliability criteria for all nuclei mentioned above (63,65Cu, 80Se, 89Y, 133Cs, 138Ba, 141Pr, 165Ho, 186W). Fiexp for all nuclei were compared with Fitheor- calculated in the frame of the CMPNR. Noticeably disagreements were obtained. The new evaluated cross sections for partial reactions (g,n), (g,2n) and (g,3n) and also for total photoneutron reaction (g,tot) = (g,n) + (g,2n) + (g,3n) were obtained using experimentally-theoretical method for evaluation reliable cross section data. For all nuclei evaluated photoneutron reaction reaction cross sections integrated cross sections were obtained for various energy ranges. Neutron emission spectra for 141Pr, 186W were calculated and published [6]. Spectra for 181Ta, 208Pb, 209Bi were calculated not in the first but in the second year. The new evaluated cross section data for all nuclei mentioned with the exception of 165Ho were published (63,65Cu and 80Se, 89Y, 133Cs, 138Ba, 141Pr, 186W) and included into the international nuclear reaction database EXFOR. 2. The 2nd CRP year 3.1. The working plan The detailed working plan for the second year is the following: 1) The energy dependencies of multiplicity transitional functions Fiexp and Fitheor will be obtained and compared for the energy range of Giant Dipole Resonance (GDR) for 103Rh, 139La, 165Ho, 197Au and additionally for 117,118,119,120,122,124Sn. 2) For all 9 nuclei mentioned above the evaluated cross sections for partial reactions and correspondent integrated cross sections will be obtained for energies of GDR by experimentally-theoretical method. 3) For selected nuclei (116Sn, 139La, 156Tb, 197Au,) neutron emission spectra will be calculated in the frame of the CMPNR. 3.2. The results obtained up to 2nd RCM Neutron emissin spectra were calculated and published for 181Ta, 208Pb, 209Bi and additionally for 116Sn. Fiexp for all nuclei were compared with Fitheor- calculated (CMPNR). Noticeably disagreements were obtained. New data for evaluated partial and total photonuclear reaction cross sections for 139La, 140,142Ce and 197Au were obtained and published. In addition to the working plan new evaluated partial and total photoneutron reaction cross section data for 59Co, 90,92Zr and 98Mo [12] were obtained. New data were obtained (103Rh, 139La, 165Ho, Bull. Russ. Ac. Sci.). For all nuclei evaluated photoneutron reaction reaction cross sections integrated cross sections were obtained for various energy ranges. All published evaluated partial and total reactions cross sections data were included into the international nuclear reaction database EXFOR.
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