Isomeric cross sections of the (n, α) reactions on the 90Zr, 93Nb and 92Mo isotopes measured for 13.73 MeV-14.77 MeV and estimated for 10 MeV-20 MeV neutron energies

Isomeric cross sections for the Zr-90(n, alpha)(87)Srm, Nb-93(n, alpha)(90)Ym and Mo-92(n, alpha)Zr-89(m) reactions were measured at five neutron energies over the range 13.73 MeV-14.77 MeV using the activation technique in combination with high resolution gamma-ray spectrometry. In the present work, the cross sections are measured for the Zr-90(n, alpha)(87)Srm and Nb-93(n, alpha)(90)Ym reactions are referenced to the Al-27(n, alpha)Na-24 standard reaction cross section whereas those measured for Mo-92(n, alpha)(89)Zrm reaction are referenced to the Fe-56(n, p)Mn-56 standard reaction cross section. The cross sections for these reactions were also theoretically estimated using the EMPIRE-3.2 and TALYS 1.8 codes over the neutrons energy range of 10 MeV-20 MeV and matched with the experimental cross sections by making a proper choice of the model parameters. A minimum eight different sets of these statistical model calculations were performed by using the consistent sets of model parameters along with the pre-equilibrium mechanism in addition to the direct-reaction and the statistical Hauser-Feshbach (HF) compound nucleus ones. The measured cross sections for these three reactions increase with the increase in neutron energy from 13.73 MeV to 14.77 MeV. As the proton number increased by one when we go from zirconium to niobium or from niobium to molybdenum, the probability of alpha particle emission also increases at each corresponding neutron energy. The present results indicate that the measured cross section at each neutron energy for the Mo-92(n, alpha)Zr-89(m) reaction is found to be the highest as compared to the other two reactions whereas, for the Zr-90(n, alpha)Sr-87(m) reaction, the measured cross section is found to be the lowest as compared to the other two reactions studied. The results obtained from the present measurement are found to be in good agreement with the calculated reaction cross section based on theoretical models and also with the work reported by earlier authors.