724 



Edgar Inselberg and J. L. Rosenberg 



between it and the sample. 



The assumption that the two phototubes will detect essentially 

 the same emission change may be checked by means of the follomng 

 procediire : 

 Let 



AT = total change at time t (corrected for flash-only change) 

 AF = change observed with interference filter at time t (cor- 

 rected for flash-only change) 

 AE = contribution of the emission change to AT 

 Ae = contribution of the emission change to AF 

 Aa = absorption change, assumed to be essentially the same in 



AT and AF 

 AE'» emission change at time t, measured independently (by P2) 

 Ae'= emission change with interference filter at time t, mea- 

 sured independently (by ?2 ) • 

 By definition 



AT = AE + Aa (1) 



AF = ite + Aa (2) 



Assuming that 



Ae Ae' . . 

 ^ « k (3) 



AE AE« 



and solving Equations 1, 2, and 3 simultaneously, we have 



AF - kAT 



Aa = — ; (U) 



1 - k 



Values of Aa calculated from Equation h can be compared with val- 

 ues obtained directly by subtracting the waveforms of the two 

 phototubes. This method coxild also be used to estimate the magni- 

 tude of absorption changes in an apparatus where emission changes 

 can be measured independently but direct corrections for emission 

 cannot be made, because of differences in phototube geometry. 



Understanding this flash-induced luminescence may prove of 

 greater value than recognizing it as a possible experimental pit- 

 fall. It is analogous in some respects to a chromatic transient 

 effect. Apparently, this luminescence represents either afterglow 

 or fluorescence. Since the monochromatic beam is well below the 

 compensation point in intensity, it is difficult to accept that 

 it could have such a large effect on the flash-induced afterglow, 

 which is feeble to begin with (as indicated by Fig. 2, A), Thus, 

 we tentatively identified this effect as a flash-induced increase 

 in the fluorescence originating from the detecting beam. 



