Preparation of the Sample for Irradiation

A sample should be prepared properly and then placed in a container before it is irradiated. The person who prepares the sample should be extremely careful not to contaminate it. Activation analysis is so sensitive that it can determine traces of elements undetectable by chemical methods. If the sample is left on a table for a certain period of time, it collects dust that acts as a contaminant. Touch by hand may transfer enough salt to cause the irradiated sample to show the presence of sodium and chlorine. To avoid contamination, samples should be handled in dry boxes or in clean rooms. The person who prepares the sample should use clean instruments (knife, file, tweezers, etc.) and also wear clean plastic gloves. 

Element Symbol Reaction Threshold energy (MeV) Half-life of product Main radiation emitted and its energy (MeV) 

Solid samples should have their surfaces cleaned with a suitable cleaning fluid to remove any surface contamination. The weight of the sample should be determined after cleaning it. For maximum accuracy, the weight is determined again after irradiation and counting are completed. 

Liquids and powders cannot be cleaned, so they are handled in clean containers, avoiding contamination from the container wall. For liquid samples, care should be exercised to avoid loss of fluid when the sample is transferred in and out of the container. In the case of powder (or powderized) samples, the observer should be certain that a truly representative sample has been prepared. This is especially important if the main sample under analysis is not homogeneous. 

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A procedure for the analysis of natural iodine in aqueous solutions of iodohippuric acid (57) has utilized a freezing technique for the preparation of the sample for irradiation. Irradiation of a frozen sample rather than a solution has a number of advantages, the pressure in irradiation containers caused by the radiolysis of water is reduced substantially losses of iodine due to vaporization and also to adsorption on container walls are greatly minimized and interference from nuclides from container walls is avoided. 

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