Effect of Neutron Irradiation on the Acoustic Performance of Evaporated CdS Films

Investigations have been carried out on the effects of neutron irradiation on the insertion loss of evaporated longitudinal CdS transducers operating in the frequency range 0.9–2.0 GHz. The one-way transducer loss was markedly reduced by irradiation and subsequent annealing, and the transducer bandwidth was also increased. Attempts were made to distinguish between the effects produced by thermal neutrons, fast neutrons, and gamma rays. The results suggest that neutron bombardment induces two opposing processes in a transducer. There is a significant improvement in the insertion loss due to the increase in resistivity, and an increase in the loss due to the lattice damage caused by irradiation, which effectively reduces the electromechanical coupling constant. The latter mechanism was investigated in several bulk samples of CdS. The effect of neutron irradiation on the film resistivity was investigated and it was found that the resistivity increased with irradiation. The measured resistivity was found to be a function of the thickness of the film, and this result was interpreted on the basis that the resistivity measured was an average or effective value of the mosaic of amorphous and crystalline CdS in the film, and was probably not a measure of the resistivity of the crystalline CdS.