Neutron-induced cross sections of short-lived nuclei via the surrogate reaction method

The measurement of neutron-induced cross sections of short-lived nuclei is extremely difficult due to the radioactivity of the samples. The surrogate reaction method is an indirect way of determining cross sections for nuclear reactions that proceed through a compound nucleus. This method presents the advantage that the target material can be stable or less radioactive than the material required for a neutron-induced measurement. In this work, we investigate whether this technique can be used to determine neutron-induced capture cross sections in the rare-earth region. We have performed an experiment to study the validity of the surrogate method for extracting neutron-induced capture cross sections. We have used the well known 175Lu(n,γ) and 172Yb(n,γ) cross sections to study the 174Yb(3He,p)176Lu and 174Yb (3He,4He)173Yb surrogate reactions. Our experimental results indicate that the angular momentum populated in the transfer reactions used is significantly higher than the one populated in neutron-induced reactions. These differences explain the big discrepancies observed between the surrogate capture measurements and the neutron-induced data. At low excitation energy, the compound elastic (n,n) decay channel is predominant and has the particularity to be extremely sensitive to the spin and the parity of the decaying nucleus. Our experimental data clearly reflect that this decay channel is not accessible in the transfer reactions we have considered. This study is extremely important in view of the application of the surrogate method to infer capture cross sections of actinides