ИСТИНА

Two different methods were used for determination of cross sections for partial photoneutron reactions, primarily (g, 1n), (g, 2n) and (g, 3n). One (Livermore (USA), Saclay (France) and some others) was based on the using of quasimonoenergetic annihilation photons and various methods of direct neutron multiplicity sorting. The second method (Moscow (Russia), Melbourne (Australia) and some others) was based on using of bremsstrahlung and obtaining of reaction yield (g, xn) = [(g, 1n) + 2(g, 2n) + 3(g, 3n) + …] cross section from which the contribution of (g, 1n) reaction was estimated by statistical theory correction and those of (g, 2n) and (g, 3n) reactions by using appropriate subtraction procedures. Experimental conditions were noticeably different and therefore significant discrepancies between the results were obtained. The most impressive were the well–known large (up to 100 % of value) systematic disagreements between Livermore and Saclay data – generally SIG(g, 1n) are larger at Saclay but SIG(g, 2n) in turn at Livermore. The situation was investigated for many nuclei using proposed objective physical criteria for data reliability: Fi = SIG(g, in)/SIG(g, xn) = SIG(g, in)/SIG[(g, 1n) + 2(g, 2n) + 3(g, 3n) + …]. By definition F1 should not be larger 1.00, F2 – 0.50, F3 – 0.33, etc.: larger values mean erroneous experimental neutron multiplicity sorting or yield reaction cross section correction and therefore unreliable data. It was found out that data under discussion for many nuclei (63,65Cu, 80Se, 91–96Zr, 115In, 112–124Sn, 133Cs, 159Tb, 181Ta, 186–192Os 197Au, 207,208Pb) are not reliable because of large systematic errors of procedures used. Experimentally–theoretical method was proposed for evaluation of data satisfied to proposed physical criteria: SIGeval(g, in) = Ftheori • SIGexp(g, xn). The competition between partial reactions was in accordance with combined model of photonuclear reactions and their sum SIGeval(g, xn) is equal to SIGexp(g, xn). Partial reaction cross sections evaluated for many nuclei differ noticeably from experimental data obtained using neutron multiplicity sorting or statistical theory correction but agree with modern data obtained using activation method. The deviations of evaluated data from experimental ones are noticeably large and therefore many important physical problems should be reanalyzed.