A Sensitive Chemical Actinometer for Ultra-violet Radiation

Abstract

THE most widely used chemical actinometer for ultraviolet radiation is based on the photochemical decomposition of oxalic acid in solutions of oxalic acid and urany 1 oxalate, and subsequent titration with hot potassium permanganate¹. This actinometer requires relatively large volumes of solution, and since the ultimate sensitivity depends on the titration difference before and after irradiation, ultra-violet sources of low dose-rate require relatively long exposure times. Actinometers in which the products of photolysis are directly determined are capable of greater sensitivity, depending on the sensitivity of the method used for analysis. Direct spectrophotometry, with high absorption of the photolysis products, introduces problems of inner filters and non-linearity of response. Parker² has devised a chemical actinometer with high sensitivity which depends on the decomposition of potassium ferrioxalate, spectrophotometric determination of the ferrous ion formed by the addition of phenanthroline and buffer solution, and subsequent measurement of absorption at 5100 Å. However, even dim electric light produces rapid decomposition of the potassium ferrioxalate, and all manipulations must be performed in a dark room.