UBC Theses and Dissertations

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UBC Theses and Dissertations

The statistical and thermodynamic theory of thermal radiation and its application to detector sensitivity. Coburn, John Wyllie


The Bose-Einstein distribution is derived, and from this the mean values and fluctuations of the thermodynamic quantities describing a volume V of black body radiation at absolute temperature T, are calculated. The problem of the energy fluctuation of a body of emissivity ε in thermodynamic equilibrium with a volume of black body radiation, is considered from a statistical approach. The result var E = kT ²C , known to be correct from thermodynamics, is obtained. The zero point energy difficulty in the mean energy of the radiation is discussed in detail. Arguments are presented supporting the inclusion of the zero point energy in the thermal radiation theory. The problem of the number of distinguishable levels that can be obtained from a certain signal power in a resonator is discussed in this section. Finally the results of the theory above are employed to determine the ultimate sensitivity of radiation detectors. Care is taken to isolate factors which are not fundamental properties of the detector, from the treatment of the detector sensitivity. A bolometer and a phototube, energy and quantum detectors respectively, are discussed in detail.

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