302 ANNALS NEW YORK ACADEMY OF SCIENCES 



Summary of Paper 



Dr. Brainin stated that X-radiation is a by-product of the collision 

 between atoms and fast-moving electrons. X-rays are electromagnetic 

 ether waves like light waves, differing from them only in wave-length 

 and frequency, the wave-length of light being about .00005 cm. and that 

 of X-rays of the order of .00000001 cm. 



We distinguish two classes of X-rays: 



1. Characteristic or homogeneous rays, which are emitted by a metal 

 when hit by electrons of proper velocity for that particular metal, which 

 in turn is determined only by the atomic weight (or number) of the 

 metal. These rays are all of the same wave-length. 



2. General radiation, which consists of ray-s of many different lengths, 

 like a spectrum from an incandescent solid. The voltage impressed on 

 the tube determines both the intensity of emission of any particular wave- 

 length and the length of the shortest wave present in the X-ray spectrum. 

 This can be determined from the formula (potential) (electronic 

 charge) = (Planck's constant) (frequency of wave). 



-In these experiments the anode was a hexagon, on each side of which 

 a different metal was attached, and which could be magnetically rotated 

 to bring the different metals under the electron stream. The X-rays 

 passed out of the tube through a mica window .001 cm. thick into an 

 ionization chamber, which completely absorbed the rays for all potentials 

 used. The intensity was measured by the usual ionization method. 



The following table shows metals used and critical voltages for pro- 

 ducing characteristic rays of each: 



Platinum (atomic weight, 195), about 100,000 volts. 

 Tungsten " " 184 " 95,000 



Silver " " 103 " 25,500 



Molybdenum" " 96 " 19,500 



Copper " " 64 " 12,000 



Cobalt " " 59 " 10,000 



The following table shows relative emissivity of these metals at differ- 

 ent voltages in descending order: 



5,700 8,200 10,000 10,700 



Ptl 



Ag/ 



Pt 



Pt 



Pt 



Ag 



Ag 



Agl 

 W i 



W 



W 



W 



Mo 



Mo 



Mo 



Co 



Cu 



Cu 



Co 



Mo 



Co 



Co 



Cu 



Cu 



2,800 



14,20( 



3 



17,500 up to 40,000 



Pt 



Pt 







Pt 



W 



W 







W 



Ag 



Co 







Co 



Co 



Ag 







Cu 



Mo 



c;u 







Ag 



Cu 



Mo 







Mo 







V. 



E. 



Levine, 

 Secretary. 



