Comparison of the effectiveness of contemporary ophthalamic lenses against beta radiation
Dunlap, J.H.; Harvey, P.W.; Schwing, R.L.
Health Physics 32(6): 555-559
1977
ISSN/ISBN: 0017-9078 PMID: 881358 Document Number: 117015
Since it is prmarily the lens of the eye which is being protected, it should be remembered that in addition to the 1.2-2.5 cm air gap between the ophthalmic lens and the cornea of the eye (providing very little attenuation of the transmitted betas), the lens of the eye is protected by the tear layer, the corneal epithelium, the cornea, and the aqueous humor: a total of about 0.375 cm, or approximately 0.394 g/cm2 thickness density. This would stop all 90Sr betas, but not much of the 32P or 90Y radiation. From the calculations and measurements presented thus far, it is evident aht safety glasses with crown glass ophthalmic lenses afford the eye the greatest protection against beta radiation, whereas street glasses with plastic ophthalmic lenses afford the eye very little protection. It is to be noted that glass stree lenses (.apprx. 2.2 mm thick) provide greater protection than plastic safety lenses (.apprx. 3.5 mm thick). Those working with unshielded beta sources that emit relatively hard beta rays should wear crown glass safety glasses. Individuals to whom this might apply include those handling unshielded beta sources. Accordingly, it might be well for all health physicists to reconsider the eye protection problem. Incidentally, for individuals not directly facing the beta sources, tempered safety glass side shields should afford the wearer additional eye protection. The reader is cautioned in choosing safety lenses which contain a large percentage of thorium (CFR75). It would be defeating the intent of the eye protection provided if such lenses caused more radiation exposure than the source being shielded against.