Abstract
An experimental method of determining the wavelength distribution of the X radiation at a point within a block of irradiated material is described. The method consists of measuring the absorption of the radiation in spherical shells of absorbing material placed round a spherical ionization chamber. The absorption curve is converted to that which would have been obtained had it been possible to use flat filters, and this curve is analysed by a method described elsewhere to give the spectral distribution of the radiation. Some illustrative examples are given.