74 APPLIED RADIOACTIVITY 



TABLE 11-11 



Coefficient of Reduction of Intensity of Gamma Radiation in 



Aluminum (/x cm -1 ) 



Element Soft Medium Hard Very Hard 



Element X in 10 8 cm Energy in Electron Volts 



RaB 0.23 -0.035 5.36 X 10 4 -3.51 X 10 5 



RaC + RaC" 0.209-0.0056 5.9 X 10 4 -2.22 X 10 6 



RaD 0.269 4.59 X 10 4 



spectroscopic results obtained by Ellis and Skinner [1924]. These are 

 the therapeutically useful gamma radiations of more than average 

 intensity. For comparison, the equivalent calculated energy in electron 

 volts that must be used to excite an x-ray tube to produce the same 

 minimum wavelengths is shown in the last column. 



Atomic Nucleus the Source of Gamma Rays 



'In the process of radioactive disintegration it has been found that a 

 beta particle in the form of a nuclear electron is ejected. This ejection 

 is followed by the emission of a gamma ray. The emission of the disin- 

 tegration electron leaves the new nucleus in a disturbed or " excited " 

 state, and as the nucleus settles down to its normal state it becomes the 

 nucleus of the next product. In the same way that optical and x-ray 

 spectra are characteristic frequencies emitted as the result of readjust- 

 ment in the electron configuration of the atom, the gamma rays repre- 

 sent characteristic frequencies associated with the readjustment of the 

 structure of the nucleus. The greater proportion of the radiant energy, 

 because of nuclear readjustment after the emission of a nuclear electron, 

 escapes from the atom, but some of it is absorbed by its planetary elec- 

 tronic structure. Consequently planetary or photoelectrons are also 

 emitted. Their energy depends on the frequency of the gamma radia- 

 tion and on the level from which the planetary electron is liberated. 



