136 



Mr. M. Ishino on the Scattering and 



by a lead plate B 1 cm. thick at A', so that the soft gamma 

 rays from radium B and radium C were practically cut off, 

 and the hard rays from radium C only were used. The 

 source, under the above-mentioned experimental arrange- 

 ment, gave a convenient value of the ionization current, 

 viz. about 10 div./nrin. in most cases. 



Aluminium, lead, and iron plates were used as the 

 absorbers and the radiators. They were all square in shape, 

 20 cm. in side and of various thicknesses. Mercury was 

 also used. The measurements of the gamma-ray activity 

 through the plates were carried out with the plates in three 

 positions : (1) close to the lead block LL at B,^ (2) close to 

 the front surface of the electroscope at R 2 , and (3) close to 

 the back surface of the electroscope at R 3 . The readings 

 due to the decaying source alone were taken before and 

 after each series of measurements at R 3 , and the intensity of 

 the source corresponding to the moment when the mea- 

 surements with the plates were performed was found. The 

 observed values of the ionization current, after correcting 

 for the natural leak of the electroscope, were expressed in 

 percentages of the corresponding intensity of the source 

 when the radiator was removed. 



§ 4. Results. 



The observed results are tabulated in the following- 

 tables : — 



Table I. — Aluminium. 



Thickness 



Mass 



of 



Unit Area 



(pi)- 



Ionization Current. 



Apparent 



Scattering 



in forward 



direction 



(S). 



of 

 Plate 



Source 

 alone. 



Plate in 

 Position 1. 



Plate in 

 Position 2. 



cm. 

 •058 



gr.-cm.- 2 

 •154 



100-0 



98-88 



99-48 



0-60 



•160 



•423 



,, 



97*56 



99-06 



1-50 



•322 



•853 



>> 



95-35 



97-95 



2-60 



•485 



1-286 



5) 



93-05 



96-95 



3-90 



•644 



1717 



)> 



91-25 



95-95 



4-70 



•965 



2-58 



)J 



88-24 



94-26 



6-02 



1-33 



3-45 



)) 



83-62 



91-81 



8-19 



1-63 



4-31 



)> 



80-16 



89-81 



9-65 



1-95 



5-18 



)> 



76-21 



86-96 



1075 



2-28 



6-05 



„ 



72-26 



84-55 



12-29 



2'44 



6-49 



>> 



69-73 



82-03 



12-30 



294 



7-80 



f) 



66-25 



79-64 



13-36 



