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Correspondence

The Hugh Adam Research Department of the Medical School and the New Zealand Branch of the British Empire Cancer Campaign, University of Otago, Dunedin, New Zealand

This excerpt was created in the absence of an abstract.

A paper by I. Opatowski (1951) has just come to my notice in which he states that Lea's "overlapping factor F" (Lea, 1947) is only a first approximation. Opatowski derives a "corrected" expression which differs substantially from Lea's even when (= 2r/L, r radius of the sensitive volume, L mean separation between ions) is as little as 0·2.