691 



TABLE 757.— ENERGY IN CALORIES/HR DEVELOPED BY ONE GRAM OF 

 RADIUM IN EQUILIBRIUM WITH ITS PRODUCTS* 



Energy radiation in Mev 

 Material Radiation a y 



88 Radium 226 ay 17.32X10 10 .... .69X10 10 



86 Radon 222 a 19.80 



84 Polonium 218 a 21.64 



(Radium A) 



82 Lead 214 p~y .... 2.35X10 10 



(Radium B) 



83 Bismuth 214 a(.04%)p-y .... 11.46 6.50 



(Radium C) 



84 Polonium 214 a 27.70 



(Radium C) 



81 Thallium 210 /T .... 6.50 



(Radium C") 



82 Lead 210 p~y .... .09 .17 



(Radium D) 



83 Bismuth 210 p~ .... 4.22 



(Radium E) 



84 Polonium 210 ay 19.53 .... 2.78 



(Radium F) 



Radiation totals in Mev 105.99X10 10 24.62X10 10 10.14X10 10 



Energy due to recoil of atom 3.71 



Alpha rays and recoil 109.70X10 10 



Total energy radiated (a, p~, y in Mev) = 144.46Xl0 10 = 199 cal/hr. 

 The total heating effect developed by one gram of radium in equilibrium with its prod- 

 ucts in 199 cal/hr. 



* For reference, see footnote 199, p. 618. 



TABLE 758.— CATHODE RAYS 



Owing to the growth of the subject, electrons are treated under three separate headings ; 

 cathode rays, the swiftly moving electrons from the cathode in a discharge tube ; beta rays, 

 from radioactive breakdown ; and the general field, electrons. The velocity of the cathode 

 rays (electrons) depends upon the applied voltage. At comparatively low pressures the 

 cathode rays have a nearly uniform velocity. Free electrons are emitted from hot bodies 

 (Table 683-689), especially if the heated substance is coated with barium, calcium, or 

 strontium oxide (Wehnelt cathode). These electrons can be given any desired speed, 

 always less than that of light, if the heated substance (usually in the form of a wire) be 

 enclosed in an evacuated tube and the difference of potential (V) applied between the wire 

 (cathode) and another electrode (anode, anticathode, or target). The speed of the electron 

 and also its kinetic energy is often designated by giving the applied voltage, i.e., a 10 kv 

 electron has a speed of 10 kv, about .2 that of light, and an energy of 10,000 ev, or 

 1.602 X 10~ 8 ergs. (See Table 713.) The speed (v) of the cathode rays, expressed as a 

 fractional part (p) of the speed of light (p = v/c, where c is the speed of light), when 

 they have fallen through the entire potential difference, is given by the formula (which is 

 corrected for the relativity change of mass) 



V = 510.8 [(1-/3 2 )- 



■1] 



where V is in kilovolts. 

 A tabulation of the corresponding values of V (kilovolts) and P follows. 



P V(,kv) 



.90 661. 



.942 1000. 



.95 1085. 



.98 2045. 



SMITHSONIAN PHYSICAL TABLES 



