In a paper published in 1996 in the Proceedings of the National Academy of Sciences (click here for pdf), Herndon discloses the rationale for a substructure within the Earth's inner core, consisting of a solid, uranium sub-core surrounded by a sub-shell of fission products and the products of radioactive decay. In describing the sub-shell, Herndon notes, "Consequently, one may anticipate the subshell to have a poorly defined crystal structure, possibly even to be a slurry or a fluid."

Herndon also notes, "The effect of nuclear activity on geomagnetic field production should not be discounted." These concepts were embryonic ideas which were to mature in a fundamental publication by Herndon eleven years later about the georeactor not only being the energy source for the geomagnetic field, but being as well the mechanism for its generation (click here for pdf).

Seismic data seem to indicate that earthquake waves travel more quickly through the inner core in a north-south direction than in an east-west direction. Herndon suggests the possibility of either an apparent or a real ellipticity of the inner core as a consequence of an inner-core magnetic field. This is a concept open for investigation. Herndon also suggests that the substructure of the inner core should be discernable when sufficiently precise seismic data are obtained.

J. Marvin Herndon (1996) Substructure of the inner core of the Earth. Proc. Nat. Acad. Sci. (USA) 93, 646-648. (click here for pdf)