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The diminution of exposure rate from radium ? radiation by filtration through platinum can be described very accurately by G0/(1 + µ0d) for wall thicknesses dfrom 0.2 mm to 4.0 mm(G0=6.356 × 10-5A m2/kg2or 8.869 R cm2h-1mg-1; µ0=1.501 cm-1).This function fits generally accepted data to within experimental error, to an accuracy not achieved by any single exponential factor. The expression is derived theoretically from a simple approximation to the spectral distribution of radium ? radiation.With this type of transmission function, the expression for the exposure rate around linear radium sources in platinum tubes (generalized Sievert integral) is readily integrated in terms of elementary functions. Used in place of the Sievert integral in calculations of dose distributions, this new formulation makes possible straightforward numerical evaluation and avoids the storage of tabulated values in computer programmes.