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

Varlamov, V.V.

Автор: Varlamov V.V.
Сборник: 1st Research coordination meeting updating photonuclear data library and generating a reference database for photon strength functions, 4 – 8 April 2016, IAEA Headquarters, Vienna, INDC International Nuclear Data Committee Summary Report
Серия: INDC(NDS)-0712
Год издания: 2017
Место издания: IAEA NDS Vienna, Austria
Первая страница: 10
Последняя страница: 12
Аннотация: Most of the partial photoneutron reactions cross sections were obtained using quasimonoenergetic annihilation photon beams at the Livermore (USA) and Saclay (France). Both laboratories employed the same method to identify reactions based on the assumption that the neutrons from partial reactions (g, 1n), (g, 2n) and (g, 3n) have quite different energies. Significant systematic discrepancies are well–known: in many cases for the same nuclei the (g, 1n) reaction cross sections are noticeably larger at Saclay, but the (g, 2n) cross sections vice versa are larger at Livermore and disagreements approach near 100 %. Because of that with the aim of investigation, explanation and overcoming mentioned disagreements under the IAEA CRP (TECDOC-1178, 2000) the Photonuclear Data Library (PDL) was generated. Evaluations based on various models were completed for many isotopes specified as important primarily for structural, shielding, biological and fissionable materials. The IAEA PDL has been extremely useful to a broad community, but it is now evident that it needs to be revised and updated: 1) using new proposed objective physical criteria of data reliability it was shown that many experimental partial photoneutron reaction cross sections, obtained for example, for nuclei 94Zr, 115In, 116Sn, 159Tb, 181Ta, 208Pb, etc. do not satisfy those criteria; 2) improved evaluation techniques was proposed and it was found out that many new and old evaluated cross sections disagree to each other; 3) for many isotopes there are experimental but not evaluated data. As objective physical criteria of data reliability the ratios Fi = SIG(g, in)/SIG(g, Sn) of the definite partial reaction cross sections SIG(g, in), where i = 1 for (g, 1n) reaction, i = 2 for (g, 2n) reaction, etc. to the neutron yield reaction cross section SIG(g, Sn) = SIG[(g, 1n) + 2(g, 2n) + 3(g, 3n) +…] were proposed. According to the definition F1 cannot exceed in magnitude 1.00, F2 - 0.50, F3 - 0.33, etc. Larger values mean incorrect (physically unreliable) determination of the corresponding SIG(g, in). Because all items of Fi ratios are cross sections negative values of those also mean incorrect data. The correspondent experimental-theoretical method was proposed for evaluation of partial of reaction cross section satisfied reliability criteria. It is based on using of SIGexp(g, Sn) not dependent on neutron multiplicity sorting and functions Ftheor calculated in the Combined Model of Photonuclear Reactions (CMPNR): SIGevali = Ftheori • SIGexp(g, Sn). That means that competition of partial reactions is in accordance with equations of the model and their correspondent sum is equal to SIGexp(g, Sn). In many cases evaluated reliable partial reaction cross sections were found out noticeably different from experimental and old evaluated data. In accordance with Scientific Scope energy dependencies of ratios Fexpi will be obtained for many other 63,65Cu, 75As, 78,80,82Se, 89Y, 103Rh, 117-124Sn, 133Cs, 138Ba, 139La, 140,142Ce, 141Pr, 145,148Nd, 160Gd, 165Ho, 186W, 197Au, etc. in addition to nuclei mentioned above. Cross sections for partial photoneutron reactions (g, 1n), (g, 2n) and (g, 3n) will be evaluated for GDR energies by experimental-theoretical method. New cross sections will be compared with available experimental cross section data obtained using modern facilities in Collaborations with Konan University (NewSubaru, Japan) and Extreme Light Infrastructure – Nuclear Physics (ELI-NP, Romania) and the results of multi-nucleon reaction yields measurements which will be carried out by activation method on the race-track microtron of the MSU SINP (Russia). Because the main reason of experimental data unreliability is complicated not direct connection neutron energy with its multiplicity, for selected nuclei (116Sn, 139La, 156Tb, 181Ta, 197Au, 208Pb, 209Bi, etc.) neutron emission spectra will be calculated in the frame of the CMPNR and analyzed. For nuclei investigated on the whole evaluated data will be prepared as ENDF files. Recommendations for updating the IAEA Photonuclear Data Library will be formulated.
Добавил в систему: Варламов Владимир Васильевич

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