A non-destructive determination of the depth distribution profile of a radionuclide by analysis of its beta-spectrum

A method is described which permits the measurement of the depth distribution of a beta-emitting tracer element in live and inert material. It is based upon the unfolding of the externally measured beta-spectrum in terms of a set of reference spectra obtained from a thin plane source and a series of known absorber thicknesses in equivalent conditions. The method has been applied for 45Ca (Esub(max)=258 keV) and for sup(115m)Cd (Esub(max)=1630 keV) and can be used for all beta-emitters in this range of energies. The optimum layer thickness for the imaginary subdivision of the subject into slices is dependent on the maximum energy of the spectrum, and ranges from 3.5 mg/cm2(45Ca) to 32 mg/cm2 (sup(115m)Cd). In practice the resolution might be 2-3 times worse than this due to statistical variations in the spectrum. The method is of particular interest if time-dependent processes are studied. Two experiments with biological material are reported to demonstrate the interesting possibilities of this method. (Auth.)