The autoradiographic study of several marine shales was undertaken in support of previous research, that was concerned with the influence of radioactivity on the transformation of certain organic constituents of marine shales into petroleum hydrocarbons. It was the purpose of the investigation to determine the location of the naturally-occurring radioactive elements, the alpha-particle-emitting members of the uranium and thorium series, with respect to the organic and inorganic constituents of the shales.This was accomplished by recording the ionizations or tracks of alpha-particles produced in the shales on sensitized nuclear emulsions, which were placed in direct contact with the individual rock sections. Several methods of exposing and analyzing the nuclear emulsions were developed and utilized in order to overcome the limitations resulting from the presence of opaque and fine-grained materials in the shales.Included in the results of the investigation are discussions of the sources of radioactivity occurring in the individual shales and a tabulation of the radioactivity concentrations associated with the organic and inorganic phases. The results for the shales investigated indicate that the inorganic constituents are, on the average, about 72 percent more radioactive than the organic matter.

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