542 



Tables 659 and 660 



RONTGEN RAYS (X RAYS) 



TABLE 659. — Energy and Efficiency of Production of Characteritsic X Rays 



The energy, E 2 , of the characteristic rays, as produced inside the anticathode for a 

 given tube and a given type of characteristic ray, varies with the material of the anticathode 

 and the voltage applied to the tube. The rays in a particular subgroup (see Table 657) do 

 not appear at all until a certain critical voltage, V , is reached, then all the rays of the sub- 

 group appear at once. Vo is given by the formula: V<> = i2.336/\ a , where V is in absolute 

 kilovolts and X a in Angstroms. In Table 657 values of X a associated with the various sub- 

 groups of emission lines are tabulated to the left of the particular lines with which they are 

 associated. 



The efficiency of production of the characteristic rays, which may be taken as 

 E 2 /E 3 , is given roughly by the formula: 



E 2 /E 3 = G[(V - v y/v] 



V>V 



where G is a constant whose dependence on the anticathode material and type of charac- 

 teristic ray has not yet been broadly investigated. For a silver anticathode and a tube 

 voltage of 50 kv, E 2 /E 3 for the K rays is about 0.48 X io -3 . Due to losses by absorption in 

 the anticathode and walls of the tube only a part of the energy generated in the anticathode 

 reaches the outside of the tube. The following table supplies some estimates of this "usable" 

 energy for tubes similar to the standard commercial types. 7 2 , which is a measure of the 

 useful characteristic ray energy, varies with voltage in a different manner than E 2 , on 

 account of the variation with voltage of the absorption in the anticathode. For V < V< 2 Vo, 

 h is roughly proportional to (V — V ) n , where n is usually between 3/2 and 2; but at 

 higher voltages some measurements indicate that h increases more slowly with voltage, 

 approaching a limiting value in the neighborhood of V = 6V . 



The relative intensities of the lines in a particular subgroup are independent of 

 voltage for a given element; the variation from element to element is often negligible over 

 long ranges of atomic number. In the K series, and at least for atomic numbers greater than 

 30, about 5/6 of the energy is contained in the two a lines; of these two, «i is the more intense 

 in the ratio 2:1. In the L series of tungsten, at 22.75 kv, the ratio of the intensities a\-.a 2 is 

 10:1; /3i:/3 2 :/3 3 :/3 4 have relative intensities 100:55:15:1; and 71:72:73:74 have 100:14:18:6. 



TABLE 660. — Energy and Quality of Emission X Rays 



Note: V is the constant direct current potential difference maintained across the ter- 

 minals of the tube. For varying voltages (as with a tube supplied directlyfrom a trans- 

 former, or with a mechanical rectifier), where V is the peak voltage and i is the average 

 current as read by a milliameter, all the values tabulated are decreased by an extent de- 

 pendent on the voltage and current wave forms for the particular outfit used, and therefore 

 difficult to specify here, i is the milliamperage tube current for tubes of the Coolidge type, 

 but not for gas-filled tubes, where there are complicating factors. E\ is the energy converted 

 per sec, inside the anticathode, into continuous spectrum X rays. {E^jk is a similar quantity 

 for the K characteristic rays. 



Smithsonian Tables 



