[ "2 ] 



XIX . A Study of the Ionization 'produced by ft and y Rays 

 at High Pressures. By D. C. H. Florance, M.A. r 

 M.Sc* 



[Plate I.] 



THE ionization produced by y rays in a closed vessel is 

 due partly to the ft rays escaping from the walls, and 

 partly to the ft rays set up from the molecules of the gas. 

 There is no definite proof that y rays ionize directly. 

 Kleeman (Proc. Roy. Soc. March 1909) has attempted to 

 separate the wall effect from the gas effect by means of the 

 magnetic deflexion of the ft rays from the wall. He has 

 also made a determination of the velocities and penetrating 

 power of the " emergent " and " incident " secondar}' ft rays 

 produced by 7 rays. Laby and Kaye (Phil. Mag. Dec. 

 1908). working with pressures up to 20 atmospheres, and 

 Wilson (Phil. Mag. Jan. 1909) with pressures up to 

 40 atmospheres, have investigated the effect of pressure 

 on the ionization produced by 7 rays in a closed vessel. 



Kovarik (Abstract Phys. Rev. Feb. 1912), by increasing 

 the pressure of the air in his ionization-chamber to about 

 20 atmospheres, has found the absorption coefficient of the 

 ft rays from RaE to be 0'0149 cm. -1 air, and of the harder 

 ft rays from Ra D to be 0'094 cm. -1 air. The writer has 

 found the absorption coefficient of the ft rays from UrX 

 to be 0*007 cm. -1 air. 



In the present paper a pressure of 80 atmospheres has 

 been attained, and the apparatus has been so arranged that 

 the ft rays emitted from different metals could be examined. 

 It was thus hoped that the absorption coefficients of the 

 " emergent " and " incident " secondary ft rays could be 

 determined, and an estimate made of the relative number 

 of ft particles from the walls and from the gas contained in 

 the ionization vessel. On account of the impossibility of 

 securing a definite cone of 7 rays and the incompleteness of 

 certain experimental data, these quantities could only be 

 approximately determined. 



Apparatus. 



The ionization vessel (fig. 1) was cylindrical, 7*4 cm. in 

 diameter and 27*5 cm. in height. The pressure, which 

 could be raised to 80 atmospheres, was measured by a care- 

 fully calibrated steel tube-gauge. A is a compound plate 



* Communicated by Prof. E. Rutherford, F.R.S. 



