Measurement of photo-neutron cross sections and isomeric yield ratios in the 89Y(γ,xn)89-xY reactions at the bremsstrahlung end-point energies of 65, 70 and 75 MeV

The flux-weighted average cross sections of the Y-89(gamma,xn; x = 1- 4)Y-89 x reactions and the isomeric yield ratios of the Y-87m,Y-g, Y-86m,Y-g, and (85m,)gY radionuclides produced in these reactions with the bremsstrahlung end-point energies of 65, 70 and 75 MeV have been determined by an activation and off-line gamma-ray spectrometric technique using the 100 MeV electron linac in Pohang Accelerator Laboratory, Korea. The theoretical Y-89(gamma, xn; x = 1-4)Y89-x reactioncross sections for mono- energetic photonshave been calculated using the computer code TALYS 1.6. Then the flux- weighted theoretical values were obtaind to compare with the present data. The flux- weighted experimental and theoretical (89Y)(gamma,xn; x =1-4)Y89-x reaction cross sections increase very fast from the threshold values to a certain bremsstrahlung energy, wherethe other reaction channels open up. Thereafter it remains constant a while and then slowly decreases with the increase of cross sections for other reactions. Similarly, the isomeric yield ratios of Y-87m,Y-g, Y-86m,Y-g and Y-85m,Y- in the Y-89(gamma,xn; x =2-4)Y89-x reactions from the present work and literature data show an increasing trend from their respective threshold values to a certain bremsstrahlung energy. After a certain point ofenergy, the isomeric yield ratios increase slowly with the bremsstrahlung energy. These observations indicate therole of excitation energy and its partitioning in different reaction channels.