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The angular-correlation technique of positron annihilation has been used to detect and measure the localized bubble state of positronium (Ps) in liquid Ne, Ar, Kr, H2, and N2 and in liquid and solid He at various pressures and temperatures. No bubble state was seen in liquid O2 or in solid Ne and Ar. The dynamics of bubble formation is not yet understood. In the cases where theoretical calculations, and adequate data, exist, viz. He, Ar, and H2, there is reasonable agreement for the momentum of the photons from the annihilation of positrons with the outer electrons of these atoms. The Ps annihilations from the self-trapped bubble state are reasonably well described in terms of a simple finite potential-well model.

Since one of the primary goals of physical research is to be able to disseminate the results through the medium of the various journals, the author has attempted, to write Section A of the thesis in a manner such that it can be submitted for publication with as few changes as possible.This would seem to be an advantage to both the writer and the school since it eliminates some duplication of effort on the.part of the former and it leads to a quicker sub¬ mittal for publication.In order to try to bridge the gap between the amount of information usually included in a published article and that included in theses, the author has included three ap¬ pendices in Section B which would fill in details and be of help to anyone attempting to do similar research. Tiie Debye Theta has been calculated from these very low temperature values of the elastic constants to give 129%for El and 234% for SCI. An analysis has been made of the error in these calculated 0^ due to experimental error in the elastic constants. The specific heats of SCI, SCI, andKBr have been calculated in this paper by using a combina¬ tion of a Debye and an Einstein term in the expression for the specific heat. These calculations indicate that the fit of such a simple theory becomes better as the ratio of ionic radii and masses increases in these three salts. We point out that in the alkali halides thus far studied in this laboratory, there is evidence that c, *=c," at about T=8~. 44Mo reason is offered for this coincidence.

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