Abstract
There is well-known problem of significant systematic disagreements between data for reactions (γ, 1n), (γ, 2n), obtained at Livermore (USA) and Saclay (France) using the method of photoneutron multiplicity sorting. The averaged ratios RS/Lint of integrated cross sections obtained at Saclay and Livermore for 19 nuclei from 51V to 239U are equal to 0.84 for (γ, 2n) and 1.07 for (γ, 1n) reactions. For 75As RS/Lint ratios for both partial reactions are very close (1.22 and 1.21) but for 181Ta - are quite different (0.89 and 1.25). Using the objective physical data reliability criteria it was found that there are serious doubts in reliability of Saclay and Livermore data. The newly evaluated reliable cross sections disagree with experimental data. In addition to unreliable sorting of many neutrons between both partial reactions many neutrons were lost - on the case of 181Ta in 1n channel, in the case of 75As in both 1n and 2n channels.
Highlights
The majority of data for the partial (γ, 1n), (γ, 2n), (γ, 3n), and total (γ, tot) = (γ, 1n)+(γ, 2n)+(γ, 3n) and (γ, S n) = (γ, 1n)+2(γ, 2n)+3(γ, 3n) reactions were obtained at Livermore (USA) and Saclay (France) using the quasimonoenergetic annihilation photon beams and the photoneutron multiplicity sorting method [1, 2]
The ratios RiSn/tL = σiSnt/σiLnt of integrated cross sections obtained at Saclay and Livermore for (γ, 1n) and (γ, 2n) reactions for 19 nuclei (51V, 75As, 89Y, 90Zr, 115In, 116,117,118,120,124Sn, 127I, 133Cs, 159Tb, 165Ho, 181Ta, 197Au, 208Pb, 232Th, 238U) [3,4,5] are presented
The experimental-theoretical method was developed for evaluating the partial reaction cross sections satisfying reliability criteria [6]
Summary
In figure 1 the ratios RiSn/tL = σiSnt/σiLnt of integrated cross sections obtained at Saclay and Livermore for (γ, 1n) and (γ, 2n) reactions for 19 nuclei (51V, 75As, 89Y, 90Zr, 115In, 116,117,118,120,124Sn, 127I, 133Cs, 159Tb, 165Ho, 181Ta, 197Au, 208Pb, 232Th, 238U) [3,4,5] are presented. Using the objective physical criteria for data reliability [6] and the experimental-theoretical method for evaluation of partial reaction cross sections it was shown that for many nuclei the main reason for definite systematic uncertainties is unreliable neutron sorting between 1n, 2n, and 3n channels [6,7,8,9,10,11,12,13,14,15].
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