Question of the Homogeneity of y-Rays. 



753 



Initial Part of the Absorption Curves of the 

 y-rays of Radium. 



Experiments involving four different dispositions were 

 carried out with screens of lead, tin, zinc, and aluminium. 

 The thick lead electroscope with base removed (fig. 17) was* 

 mounted on an iron tripod. Various thicknesses of metals- 

 were clamped up to form the base. In disposition 1, 6*7 rag.. 

 of radium bromide were placed at the apex of a cone of 

 height 11*5 cm. and of base 3 cm. in diameter, cut out of a 

 cylindrical lead block 12*7 cm. long and 10*5 cm. diameter. 

 The cylinder was placed immediately underneath the electro- 

 scope, the top of the former being about 3*5 cm, from the 

 base of the latter. Disposition 2 was exactly the same as 1, 

 except that 1*24 cm. of lead was placed on the lead cylinder 

 over the base of the cone. In dispositions 3 and 4 the rays- 

 were not confined by a cone at all. In 3, 0*47 rag. of radium 

 bromide, lying without cover in a recess in a lead block 1 cm. 

 thick, was placed 14 cm. below the electroscope. 4 was the 

 same as 3, except that 1*24 cm. of lead was placed directly 

 over the radium. Table V. gives a summary of the results 

 obtained with these dispositions over the ranges of thicknesses 

 of metals described. 



Table V. 



Disposition. 



Metal. 



100 x x 7 . 



a 



Eange in cm. 



Shape of 

 Absorption Curve. 



1. 



2. 



3. 

 4. 



Al. 

 Al. 

 Al. 



Al. 



2-78 to 422 







776 



404 



0-8 to 2-4 

 06 to 2-4 

 0*9 to 26 

 03 to 2-6 



Continuously concave. 

 Parallel to axis of* T. 

 Straight. 

 Straight. 



1. 



2, 

 3. 

 4. 



Zn. 

 Zn. 



Zn. 



Zn. 



301 to 421 

 1-29 to 385 



5-05 



3-39 



0-35 to 26 

 0-35 to 2 6 

 0-35 to 26 

 0-35 to 26 



Continuously concave. 

 More concave than 1. 

 Straight. 

 Straight. 



1. 



2. 

 3. 

 4. 



Sn. 

 Sn. 

 Sn. 

 Sn. 



4-11 to 535 



2-21 to 480 



5-55 



3-65 



0-5 to 205 

 05 to 2-05 

 0-5 to 2-05 

 05 to 205 



Continuously concave. 

 More concave than 1. 

 Straight. 

 Straight. 



1. 

 2. 

 3! 

 4. 



Pb. 

 Pb. 

 Pb. 

 Pb. 



10-5 to 6-67 0-3 to 2-4 



7-37 to 5-53 ; 0-3 to 2-4 

 5-32 0-3 to 24 



Continuously convex. 



Continuously convex. 

 Straight. 



Phil. Mag. 8. 6. Vol. 19. No. 113. May 1910. 3 C 



