724 Dr. J. A. Crowther on "J" Radiation. 



radiator is not purely scattered radiation, but consists of a 

 mixture of scattered radiation of the same wave-length as 

 the primary, together with a fluorescent radiation of greater 

 wave-length. In this case the radiation entering the 

 chamber C s should be given by an equation of the form 



where X and V are the coefficients of absorption of the 

 scattered and fluorescent radiations, and l\ and h. 2 the quan- 

 tities of the radiation of each type emitted by the radiator. 

 From this we have 



8/P=$ + # e -( x '- x K 



-to -to 



This equation can be solved graphically by plotting the 

 values contained in column III. against the corresponding- 

 thicknesses, and determining the slope of the curve at 

 various points. The slope of the curve for a thickness d 



.should be given by — pr(X' — X)e~ {x ' " X)d . On plotting the 



logarithms of these numbers ao-ainst the thickness a straight 

 line should be obtained, the inclination of which should 

 give the value of (V — X). The graph actually obtained is 

 shown in the lowest curve in fig. 2, and the points are found 

 to lie practically on a straight line except for a slight 

 increase in slope near the origin*. The value of (V — X) 

 was found to be 3*3 cm. -1 . The corresponding value of 



k 



^ is 0'39. Substituting these values in the formula, the 



calculated values were found to agree with the experimental 

 values given in column III. to an accuracy of about 2 per 

 cent. 



Assuming that the scattered radiation is of the same 

 quality as the primary, the value of X is 2'81 cm -1 . The value 



of V is therefore 6-1 cm" 1 . The value of ^ is 0*42. The 



-^ o 



radiation from the aluminium radiator would therefore 



appear to consist of nearly equal parts of true scattered 



radiation, and a fluorescent radiation the coefficient of 



* This probably indicates the presence of a small amount of still 

 softer radiation, but the accuracy of the experiments is not sufficient 

 to warrant a closer analysis of the curves. 



