The effect of excitation beam absorption on measured values of fluorescence has been studied wlth a computer-centered spectrofiuorimeter capable of measuring fluorescence and absorbance slmuitaneously. This effect appears to be independent of the nature of the absorbing species and the excitation and emisslon wavelengths. A model is proposed and tested which corrects fluorescence, observed at 90°, for the attenuation of the excitation beam caused by the absorbance of the fluorophore and any chromophores present in the cell. The resuitlng absorptlon-corrected fluorescence is linear with the concentration of the fiuorophore in solutions wlth total absorbances as high as 2.0.

A computer centered spectrophotometer-spectrofluorimeter combination instrument has been fabricated that will allow simultaneous absorption and fluorescence measurements.The dedicated computer applies corrections to the data collected for many of the instrumental and photophysical variables of fluorescence measurements.

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Relative fission yields of ten nuclides produced by proton-induced fission of natural uranium and U 235 were determined at several proton energies in the range 12 to 20 Mev. The expected trend toward symmetric fission at increased energies is observed. A statistical relation is used to correlate this shift in fission symmetry with the excitation energy of the compound nucleus.