Radiocolloid

a colloid whose dispersed phase is made up of radioactive substances of low solubility in extremely dilute solutions. As established by the work of I. E. Starik and other investigators, radiocolloids possess a dual nature. One way of regarding radiocolloids is as ordinary colloids with solid particles (dispersed phase) consisting of molecules containing radioactive atoms. Such radiocolloids, known as true radiocolloids, arise only when the content of the radioactive substance in solution exceeds the concentration corresponding to a saturated solution. For poorly soluble substances, the saturation concentration may be very low (10¹⁰ mole/liter and lower); thus, the formation of colloid particles is possible in extremely dilute solutions.

A second way of regarding radiocolloids is as a system arising from the sorption of radioactive atoms or the ions and molecules containing these atoms on the solid ultramicroscopic particles that are usually present in water. Radiocolloids of this type, or pseudoradiocolloids, may exist in solutions of radioactive substances having concentrations both above and below the concentration of a saturated solution. The conditions necessary for forming true radiocolloids differ from those for pseudoradiocolloids, and a mixture of both types of radiocolloids is usually present in a solution.

As a result of the formation of radiocolloids, the behavior of radioactive atoms changes markedly. The atoms will no longer enter into chemical reactions or will react at very low rates. The existence of colloid particles in extremely dilute solutions depends mainly on the physicochemical properties of an element and not on the element’s radioactivity. Under analogous conditions, both radioactive and stable atoms of a given element form colloids similar in nature.