Radiation Labelling with Carbon-14 of Aliphatic Hydrocarbons

Abstract

RADIATION labelling techniques have been successfully developed to introduce tritium atoms in a number of organic molecules¹. Such a method may also be applied to preparation of carbon-14-labelled compounds, taking advantage of radiation-induced reaction between an organic substance and that containing the radioisotope. Preliminary reports² describe the identification of a number of radioactive carboxylic acids in mixtures containing hydrocarbons (or heterocyclic compounds) and carbon-14-dioxide irradiated with X- or beta-rays. Substantially better results, as regards the amount of radioactivity incorporated into the reaction products, have been now attained in the radiation labelling of aliphatic hydrocarbons promoted by high doses of gamma-rays (from spent elements of nuclear fuel) in gaseous systems containing labelled methane as the source of radiocarbon, a saturated hydrocarbon of low molecular weight and an inert gas. Typical experimental conditions were as follows : a mixture of 0.75 m.mole of radioactive methane (specific activity 0.5 mc./m.mole), 0.75 m.mole of propane and 3.0 m.moles of xenon was irradiated in a sealed ‘Pyrex’ ampoule (125 c.c. approximate capacity). Addition of xenon increased considerably the energy transfer from ionizing radiation to the hydrocarbon mixture, as shown by preliminary runs. The irradiation dose was estimated to be 0.99 × 10⁸ rads.