Deflexion of a Particles through Large Angles. 617 



Table IV. 



Variation o£ Scattering with Atomic Weight. (Example of 



a set of measurements.) 



I. 



Substance. 



II. 



Atomic 



weight. 



A. 



III. 



Air 



equivalent 



in cm. 



IV. 



Number of 

 scintillations 



per minute 



corrected for 



decay. 



V. 



Number N of 



scintillations 



per cm. air 



equivalent. 



VI 



,3/2 



A . 



VII. 



2/6 



NXA . 



Gold 



197 



119 



107-9 

 63-6 

 27*1 



•229 

 •441 

 •262 

 •616 

 2-05 



133 

 119 



517 



71 



71 



581 

 270 

 198 

 115 

 34-6 



2770 



1300 



1120 



507 



141 



021 

 0-21 

 0-18 

 0-23 

 024 



Tin 



Silver 



Copper 



Aluminium.. 



The combined results of four experiments are given in 

 Table Y. In the last column are given the ratios of the 

 numbers of scintillations per centimetre equivalent to A 3/2 . 

 This ratio should be constant according to theory. The 

 experimental values show a slight increase with decreasing 



atomic weight. 



Table V. 



Variation of Scattering with Atomic Weight, 

 results using Ra 0.) 



(Collected 



Substance. 



Total number 



of scintillations 



counted for each 



material. 



A 3 ' 2 . 



Ratio of 

 scintillations per 

 cm. air equivalent 



to A 3/2 * 



Gold 



850 

 200 

 700 

 800 

 600 

 700 



2770 

 2730 

 1300 

 1120 

 507 

 144 



95 

 99 

 96 

 98 

 104 

 110 



Platinum 



Tin 



Copper 



Aluminium 



* Note 1. — Since these experiments were carried out, Richardson and 

 one of us (Phil. Mag. vol. xxv. p. 184 (1913)) have determined the masses 

 per unit area per cm. air equivalent for different metals, using- the scintil- 

 lation method. Introducing the results, and calculating the values of 

 the ratio of the scattering per atom divided by A 2 , the following are 

 obtained :— Au 3-4, Pt 3% Sn 3-3, Ag 3*6, Cu 3*7, Al 3-6. These 

 numbers show better agreement than those in the last column above, 

 which are calculated on the assumption of Bragg's law. 



