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Description of the properties of unattached 218Po and 212Pb particles by means of the classical theory of cluster formation.

A review is given of the classical theory of cluster formation to see whether it is a useful description of the behaviour of unattached radioactive particles. Special attention is given to the predictions concerning the size of the clusters, their growth, and their dependency on humidity and other trace gases. The theory is compared with the experimental observations of the last two decades. It is found that the theory predicts most of the properties of 218Po and 212Pb particles. It cannot explain the conflicting results regarding the humidity dependency of the unattached particle size. An important prediction of the theory is the failure of the unattached particle concept in some environmental conditions.