Cross Sections for theV51(γ,π−2n)Cr49Reaction

Cross sections from threshold to 300 MeV have been determined for the ${\mathrm{V}}^{51}(\gamma ,{\pi }^{-}2n){\mathrm{Cr}}^{49}$ reaction from measurements of the ${\mathrm{Cr}}^{49}$ radioactivity produced in high-energy bremsstrahlung irradiations of natural vanadium metal targets. The observed cross sections rise to 100 μb at 210 MeV and then decrease to 40 μb at 300 MeV. The cross sections are interpreted in terms of a mechanism in which the pion-production process is considered to be a single-nucleon process and the recoiling proton interacts with the nucleus to cause the emission of two neutrons. In the calculations the pion-production cross sections in ${\mathrm{V}}^{51}$ are obtained by using the free-nucleon cross sections and assuming the $A^{\frac{2}{3}}$ dependence that is indicated by previous pion yield measurements. The gross features of the observed cross sections for the ${\mathrm{V}}^{51}(\gamma ,{\pi }^{-}2n){\mathrm{Cr}}^{49}$ reaction can then be reproduced by using reasonable values for the branching ratios for the emission of two neutrons.