SPIN DISTRIBUTION FACTORS FOR FORMATION OF METASTABLE STATES OF Y-90 AND Y-91 THROUGH (N,P) REACTIONS OVER NEUTRON ENERGIES 5-15 MEV

The variations in the isomer ratio with the spin distribution factor w ere studied to obtain the cross-sections for formation of metastable s tates of Y-90 and Y-91 nuclei formed respectively through Zr-90(n,p)Y- 91(m) and Zr-91(n,p)Y-91(m) reactions over the neutron energy range 5 to 15 MeV. The theoretical values of the cross-sections could be obtai ned very close to the respective literature experimental values by var ying the spin distribution factor from 1.5 to 2.75. The limiting value of the cross-section was derived from the maximum value of the isomer ratio at that neutron energy, and for this the spin distribution fact or was found to vary from 2 to 3.5 over the neutron energies 5 to 15 M eV. Using enriched zirconium targets, cross-sections for formation of Y-90(m) and Y-91(m) nuclei at 14.8 MeV neutron energy were also measur ed in the laboratory; the values obtained are 17 +/- 2 mb and 22 +/- 2 mb respectively for Y-90(m) and Y-91(m). Both these values are close to the corresponding limiting cross-sections at 14 MeV neutron energy. (C) 1998 Elsevier Science B.V.