5^6 



Table 642 



RADIOACTIVITY 



BETA RAYS 



/3 rays are negatively charged particles (electrons) of the same nature as other electrons. 

 It seems settled that the /3 particle is emitted first; the y ray is emitted from the atom re- 

 sulting after the disintegration of the nucleus caused by the emission of the /3 particle. In 

 emitting rays (random in direction) the original element is shifted one place to a next 

 higher atomic number. Therefore one emitted electron is nuclear. Recent work proves some 

 to be extra-nuclear. The velocity of the /3 particles is such that it is necessary in dealing with 

 them to consider the Lorentz-Einstein equation, m = Wo (i — /3 2 )~ 1/2 ; m being the mass 

 of a very slowly moving electron, 0, the ratio of the velocity of the particle to that of light, V . 



The /3 and y rays are best designated by their spectra. A complete compilation of these 

 would be beyond the scope of these tables. See Kovarik and McKeehan, Nat. Res. Council, 

 Bull. 51, 1929; or Rutherford, Chadwick, Ellis, radiations from radioactive substances. 



The absorption coefficients (/*) are not precisely defined by the relation I = I e'l**, but 

 they are of great value in practical work and for the rapid diagnosis of a radioactive sub- 

 stance. It appears desirable to include them and to give also the limits of velocity of the 

 /3-ray spectra. 



* B = band, L = line. Bands originate in the primary (nuclear) rays; lines in the photo-electrons of the 

 gamma rays. 



11/p is the mass absorption coefficient (p = density); D is the thickness in which the radiation is reduced to 

 half value and = 0.69315/x. All data refer to aluminum as the absorbing material. 



Smithsonian Tables 



