| Popis: |
The method used at the National Bu~ reau of Standards for the calibration of strontium-90 + yttrium-90 beta-particle ophthalmic applicators in terms of ab sorbed dose to water, is described. The method involves measurement of ioniza tion density at the applicator surface with an extrapolation chamber. correc tion for the difference in backscatter be tween the collection electrode and water, and application of the BraggGray equation. The calibration obtained is an average over the active surface of the applicator. The overall uncertainty of the surface calibration is about ± 15 percent. |
