Reliability of partial photoneutron reaction cross sections and neutron energy spectra for 116Sn

Varlamov, V.V.; Ishkhanov, B.S.; Orlin, V.N.

Авторы: Varlamov V.V., Ishkhanov B.S., Orlin V.N.
Сборник: Международная конференция «Ядро-2017» (67-е Совещание по ядерной спектроскопии и структуре атомного ядра), 12-15 сентября 2017 г., Алматы, Республика Казахстан. Тезисы
Тезисы
Год издания: 2017
Место издания: РГП «Институт ядерной физики» Алматы, Республика Казахстан
Первая страница: 32
Последняя страница: 32
Аннотация: Many cross sections of total and partial photonuclear reactions were obtained using quasimonoenergetic annihilation photon beams at Livermore (USA) and Saclay (France). Both laboratories used similar methods to separate reactions with different multiplicities based on the assumption that the neutron spectra of (g, 1n) and (g, 2n) reactions are noticeably different. Because of those many neutrons are unreliably transmitted from one partial reaction to another. At Livermore for many nuclei the (g, 1n) reaction cross section decreases up to appearing of physically forbidden negative values and the (g, 2n) reaction cross section vice versa increases up to values for which the data reliability criterion F2 = SIGMA(g, 2n)/SIGMA(g, xn) = SIGMA(g, 2n)/SIGMA[(g, 1n) + 2(g, 2n) + 3(g, 3n) + …] have physically unreliable values larger 0.50. Such effects are very impressive for 116Sn. At energies ~ 21-26 MeV there are many negative values of (g, 1n) reaction cross section correlated with F2 > 0.50 values. Additionally in contradiction to the definition F2 noticeably decreases at energies larger ~ 23 MeV, though the energy threshold of (g, 3n) reaction B3n = 27.4 MeV. So it should be concluded that the data for both partial reactions are not reliable. To evaluate the reliable partial reactions cross sections the experimental-theoretical method was proposed. The only experimental reaction cross section SIGMAexp(g, xn) free from problems of experimental determination of neutron multiplicity was used and shared into the partial parts using the equations Ftheori = SIGMAtheor(g, 1n)/SIGMAtheor(g ,xn) of the combined model of photonuclear reactions (CMPNR). The evaluated cross sections were obtained as SIGMAeval(g, in) = Ftheori • SIGMAexp(g, xn). To investigate the connection of neutron multiplicity with its energy in details the energy spectra of neutrons from the reactions (g, 1n), (g, 2n), (g, 3n), and (g, 4n) on 116Sn were calculated in the frame of the CMPNR. The spectra were obtained for 116Sn nucleus excitation energies Eexc = 20, 30, and 40 MeV and for neutrons of various chances – the unique neutron from the (g, 1n) reaction, both neutrons from (g, 2n) reaction, etc. It was obtained that the neutrons with high energies up to Eexc-Bn are presented in all spectra. But the maxima of spectra for various Eexc are placed at near energies about 0.7 – 1.0 MeV. It means that the connection of the neutron multiplicity and its energy is very complicated. This is the main reason of significant systematic uncertainties of experimental data obtained using the method of neutron multiplicity sorting and therefore of many unreliable photoneutron partial reaction cross sections.
Добавил в систему: Варламов Владимир Васильевич

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Reliability of partial photoneutron reaction cross sections and neutron energy spectra for 116Snтезисы доклада

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