A cheap, robust, radioactive source in sheet form has been designed and constructed from commercially available material. Log-related isotopic dilutions of the source have been used to prepare a Standard Radioactive Scale. 2. The Standard Radioactive Scale has been developed as a method of internal standardization of whole-body autoradiography and its use as an aid to quantitative determination is discussed. 3. The distribution of radioactivity in the sheet source is sufficiently uniform to allow its use for high resolution radiography of thin specimens. This radiographic technique has been applied to whole body sections to demonstrate differences in quenching by tissues and to examine calcification in the rat foetus.
