Место издания:Joint Institute for Nuclear Researh Dubna, Russia
Первая страница:48
Последняя страница:48
Аннотация:There is the old and well-known problem of significant disagreements between data on partial photoneutron reaction cross sections obtained using beams of annihilation quasimonoenergetic photons the method of neutron multiplicity-sorting at Livermore (USA) and Saclay (France). It was obtained that for 19 nuclei 51V, 75As, 89Y, 90Zr, 115In, 116,117,118,120,124Sn, 127I, 133Cs, 159Tb, 165Ho, 181Ta, 197Au, 208Pb, 232Th, 238U as a rule (g,1n) reaction cross sections are larger at Saclay, but (g,2n) cross sections vice versa larger at Livermore. The averaged ratio SIGMA-Sint/SIGMA-Lint of integrated cross sections for Saclay data to those for Livermore data is equal to 1.08 in the case of (g,1n) reaction but 0.83 in the case of (g,2n) reaction. Using the objective physical criteria for data reliability and the experimental-theoretical method for evaluation of partial photoneutron reaction cross sections it was shown that many experimental data are nor reliable because do not satisfy the mentioned criteria and that the main reason is unreliable (erroneous) sorting of many neutrons between 1n and 2n channels. For 75As and 181Ta, the positions of which in the systematics for SIGMA-Sint/SIGMA-Lint ratios are specifically large, 1.21 and 1.25, correspondingly, it was found that many neutrons in various channels were lost.
The evaluation of partial reaction cross sections for 127I using physical criteria of data reliability is of large interest because SIGMA-Sint/SIGMA-Lint = 1.34 [4, 5] is the largest value in the systematics mentioned above. New reliable partial and total photoneutron reaction cross sections for 127I were obtained as SIGMAeval(g,in) = Ftheori SIGMAexp(g,xn) using Saclay SIGMAexp(g,xn) and Ftheori calculated in the combined model of photonucleon reactions (CMPNR). The significant disagreements between evaluated and experimental data were obtained and discussed in detail.
The research was carried out in the Department of Electromagnetic Processes and Atomic Nuclei Interactions of the MSU SINP. It is supported by the Coordinated Research Project (F41032, the Research Contract 20501) of the International Atomic Energy Agency.
