Self-shielding, activation analysis

While high sensitivity has been obtained in the examination of pure materials, a far more rigorous test of the activation method is found in its application to materials of a more complex matrix. Emission and X-ray spectrometry and direct spark source mass spectrometry are all restricted by the lack of suitable standards when applied to materials of complex composition. Provided that precautions are taken to avoid self-shielding errors radioactivation is largely independent of the nature of the matrix material. It is this advantage which has enabled activation analysis to prove such an invaluable tool in geochemistry. 

In most cases, as a fluence monitor small disks or wires of an Al-Co alloy with 0.1 to 1% Co are used by such a dilution of the monitor substance, self-shielding and flux depression effects are avoided. In general, since interfering radionuclides produced in the diluting element are small, chemical separations before activity measurement of Co are normally not needed. Frequently, the cobalt impurities in stainless steels, which are in the range of 100 to 1000 ppm, can be directly used as a fluence monitor in such cases, however, the accurate cobalt concentration in the material has to be additionally determined by chemical analysis. 

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