Аннотация:The objective physical criteria were proposed for investigation of the reliability of data on partial photoneutron reaction cross sections obtained using beams of quasimonoenergetic annihilation photons and the method of photoneutron multiplicity sorting. According to definition the ratios Fi = SIGMA(g, in)/SIGMA(g, xn), where (g, in) is the reaction with definite multiplicity and (g, xn) = (g, 1n) + 2(g, 2n) + … is the neutron yield reaction, should not have values larger 1.00, 0.50, 0.33,… for i = 1, 2, 3, …. If for experimental data those ratios have larger values it means that photoneutron multiplicity sorting was carried out unreliably. Using those criteria it was found out that for many medium and heavy nuclei from Cu to Bi data on cross sections of partial reactions (g, 1n), (g, 2n) and (g, 3n) are not reliable because do not satisfy to the proposed objective physical criteria. Using specially proposed experimental–theoretical method ((SIGMA-eval(g, in) = Fi-theor • SIGMA-exp(g, xn)) for partial photoneutron reaction cross sections evaluation new data satisfied reliability criteria were obtained. It was shown that those data do not agree with data obtained neutron multiplicity sorting but agree with the results of alternative experiments, first of all carried out using activation method for identification of definite partial reaction as reactions with different nuclei in final states.
The criteria and evaluation method described above were used for obtaining new reliable partial photoneutron reaction and total photoneutron reaction cross section data for 141Pr and 186W for GDR energy ranges. Evaluated data were compared with the results of the experiments carried using various photon beams (quasimonoergetic annihilation and tagged photons, bremsstrahlung) and methods (neutron multiplicity sorting, activation).
The research is carried out in the MSU SINP Department of electromagnetic processes of atomic nuclei and is supported by the Coordinated Research Project (F41032, the Research Contract 20501) of the International Atomic Energy Agency.