The Genetic Effect of Incorporated Radioisotopes: The Transmutation Problem

Radioactive decay by (-particle emission is accompanied by a chemical change or transmutation of the parent atom to one of different atomic number. The basic premise in the use of the transmutation phenomenon in biological investigations is that a molecule containing a radioactive nuclide will be subject to a certain probability of disintegration on the decay of the incorporated radioactive nuclide. At first glance it seems obvious that a molecule containing H3, C14, p32, p33, S35, or Ca45 will tend to decompose as these elements transmute to He3, N14, S32 or S33, Cl35, and Sc45, respectively. Biological effects following decay of a particular atom could, it would seem, be directly attributed to the molecule into which the atom was built. For example, any effect that could be shown to be due to the transmutation of C14 incorporated into thymidine would necessarily be due to an effect of thymidine and, by extrapolation, an effect of deoxyribonucleic acid. On the other hand, any effect due to the transmutation of S35 would seem not to be due to the participation of nucleic acids. There are two major difficulties in the interpretation of data purporting to show a transmutation effect. The first is the problem of separating the effects of radiation accompanying radioactive decay from the chemical effect due to the transformation of the nuclide. In interpreting the effects of incorporated P32 on a system some method must be found to evaluate separately the contribution of the ,particle produced in the reaction P32 -> S32 + (. The second problem is one of a precise definition or interpretation of the transmutation effect on the parent molecule and its surroundings. The effects of the complete transmutation process are due first to the liberation of A-particles and second to the effects of the process on the nuclide and on the molecule. These include the possible production of a hole