It’s been known for some time that the ratios of isotopes of mercury in fluorescent light bulbs depart from the natural ratios. The explanation given for this effect is that the different isotopes of mercury are fractionated into different areas of the light bulb. Some of the isotopes preferentially enter into the glass tube and others remain in the bulk reservoir. A question that has come up from time to time is how solid this explanation is, and whether other possibilities such as LENR might have been prematurely ruled out. A version of this question recently came up in a thread on the Rossi v. Darden lawsuit. In reply, Paradigmnoia provided a reference to the doctoral dissertation of Chris Mead, in which he reported that (1) he saw significant changes in ratios in the isotopes of Hg above their natural abundances, as seen in earlier studies; and that (2) he observed that whole-lamp ratios for Hg were not significantly different from the natural ratios. Mead’s dissertation appears to describe work presented several years earlier at a 2010 meeting of the American Geophysical Union.
How was this research carried out, is it solid, and what conclusions can be drawn from it? Is this research adequate to contraindicate transmutations via LENR as a possible explanation for the isotopic changes in Hg in fluorescent light bulbs, either in general or in this specific instance? Are there flaws or unexamined assumptions that weaken the conclusions? How does this study compare to other studies?
One interesting detail to come to light in the Mead work is that there are two kinds of fractionation — mass-dependent fractionation and mass-independent fractionation. Mead saw no straightforward relationship between isotope mass and extent of fractionation (p. 27), and the pattern of fractionation was entirely different from that reported in a number of earlier studies. Mead proposes a mechanism for this mass-independent fractionation in which the abundance of an Hg isotope is inversely proportional to its fractionation and relates the amount of "trapped Hg" (Hg trapped in the glass) to the amount of Hg in the bulk reservoir.
Twelve 14-watt bulbs were used in all, 3 as blanks. Whole-lamp assays were carried out with 2 bulbs, one with 0 hours of operation and the other with 3600 hours; trapped-Hg assays were done with 5 bulbs; and bulk-Hg only assays were done with 2 bulbs. Following is a table from the dissertation that summarizes the results (p. 29):