Physical Reliability Criteria and Special Features of Data on the Photodisintegration of ${}^{{75}}$As, ${}^{{127}}$I, ${}^{{181}}$Ta, and ${}^{{208}}$Pb Nuclei

Abstract

The known problem of significant systematic discrepancies between the cross sections obtained for partial photoneutron reactions using beams of quasimonoenergetic annihilation photons by means of neutron multiplicity sorting at Saclay (France) and Livermore (USA) is considered in detail for ${}^{75}$As, ${}^{127}$I, ${}^{181}$Ta, and ${}^{208}$Pb nuclei by employing objective physical criteria of data reliability. The integrated-cross-section ratios $\sigma_{\textrm{S}}^{\textrm{int}}/\sigma_{\textrm{L}}^{\textrm{int}}$ obtained for ($\gamma,1n$) and ($\gamma,2n$) reactions on the basis of data from the two laboratories in question differ significantly for the last three of the aforementioned nuclei but are nearly coincident for the ${}^{75}$As nucleus. For all four nuclei, the cross sections for $(\gamma,xn)=(\gamma,1n)+2(\gamma,2n)+3(\gamma,3n)$ photoneutron-yield reactions differ significantly even at photon energies below the thresholds for the ($\gamma,2n$) reaction, in which case no problem of neutron multiplicity sorting arises. Experimental data on partial and total photoneutron reaction cross sections for ${}^{75}$As, ${}^{127}$I, ${}^{181}$Ta, and ${}^{208}$Pb nuclei are compared with their counterparts evaluated within the experimental–theoretical method that employs data reliability criteria. It is found that the discrepancies of several tens of percent between the cross sections obtained for the ($\gamma,xn$), $(\gamma,sn)=(\gamma,1n)+(\gamma,2n)+(\gamma,3n)$, and ($\gamma,1n$) reactions at Livermore and evaluated data are due to an unjustified and unreliable underestimation of the cross section for the ($\gamma,1n$) reaction because of the loss of a significantly number of neutrons from this reaction.