Gamma irradiation of flint glasses for optics in ITER

Abstract

A few types of flint glasses intended for use in achromat lenses of optical diagnostics in ITER were tested recently in a nuclear reactor and demonstrated sufficient resistance to fast neutron fluences from 1012 to 1016 n/cm2. However, there is an evidence that some flint grades may have significant transient radiation-induced absorbance whereas post-irradiation measurements do not reveal any degradation. Though the effect of the short-term absorbance has been discovered at much higher gamma dose rate than it is expected in the port cell, the possible transient effect of gamma irradiation on the candidate flint types should be checked. Two grades of candidate radiation-resistance flints (F108 and TF200) for H-alpha and Visible spectroscopy were irradiated in the Co-60 gamma source at the dose rate of ~10−2 Gy/s with in-situ monitoring of their relative transparency. As a result, none of the tested samples has demonstrated significant transient absorption. The slight transmittance decrease of F108 sample was almost fully recovered in a few hours after the irradiation. The TF200 samples preserved their properties within the measurement accuracy. The results prove that the both F108 and TF200 flints can be used for diagnostic optics in ITER.