146 



RADIATION BIOLOGY 



T = /2//1 = transmittance of sample (includes reflection 

 losses) . 

 100 T = % T = percentage of transmittance. 



Ti = I/Io = internal transmittance of sample, corrected 

 for reflection losses, window absorption at 

 interfaces, and cell windows. 

 Ai = — log Ti = log 1/Ti = log lo/I = internal absorb- 



ance of sample, 

 a, = A.,/b = absorbance index, or absorbance per unit 



thickness. [ (3-12) 



D = log III l\ = density, an absorbance term applied to 

 nonspectral determinations such as the 

 blackening of photographic emulsions. 

 /„ = /o — / = absorbed flux. 



a = 1 — Ti = absorptance, or proportion absorbed by 

 sample. This quantity is of special inter- 

 est in analysis of action spectra, since a is 

 approximately equal to /x at low values of 

 absorptance. 



MuUicomponent Systems. These terms relate to homogeneous mix- 

 tures such as solutions in which the absorption of one constituent, usually 

 the solvent, is canceled out of the measurement by a comparison cell of 

 that constituent. Following the notation of Fig. 3-4&, 



T^oiv = I'/I'o = internal transmittance of comparison cell containing 

 solvent or solution lacking the unknown constituent; 

 and 



Tgoin = ///o = internal transmittance of cell containing complete 

 solution. 



If identical, matching absorption cells are used, reflection and window 

 losses are nearly the same, and only the internal transmittance need be 

 considered. When the solute contributes appreciably to the refractive 

 index, however, correction for differences in reflection at the solution- 

 glass interfaces may be required. Then 



Ts = T'soin/Tsoiv = transmittancy of unknown constituent 



of sample. 

 lOOTs = % Ts = percentage transmittancy. [ (3-13) 



^8 = — log Ts = log l/Ts = ahc = absorbancy. 

 tts = As/ be = absorbancy index (absorptivity K). 



If c is in grams per liter and b is in centimeters, the 

 unit is liters per gram-centimeter. 

 Gm = molar absorbancy index (molar absorptivity). 



If c is in moles per liter and b is in centimeters, the unit is 

 liters per mole-centimeter. 



