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Correspondence

Department of Physics Applied to Medicine, Middlesex Hospital, W.1

This excerpt was created in the absence of an abstract.

In an attempt to produce a water-equivalent medium, Jones and Raine (1949) have suggested a recipe for a phantom material (Mix D) consisting of a paraffin wax and polyethylene base loaded with magnesium and titanium oxides. They reported that measurements on the mixture, using the double ionization chamber and differential filter apparatus described by Spiers (1946), gave a linear absorption coefficient corresponding to an atomic number of 7·47, in good agreement with the calculated value of 7·42.