710 TABLES 794-801.— COSMIC RAYS 244 



Cosmic rays are an ionizing radiation that has been discovered in the atmos- 

 phere of the earth. As generally discussed these rays are divided into primary 

 and secondary cosmic rays, the primary rays being the high-energy particles 

 that fall upon the outer atmosphere of the earth. In general, the intensity of 

 cosmic radiation is given as the number of rays per cm 2 per second. The in- 

 tensity (i.e., number of particles per cm 2 ) increases for about the first one- 

 tenth of the atmosphere where it is about 5 times the initial intensity and from 

 there down to sea level the intensity decreases. These primary rays appear to 

 come from all directions from outer space and to consist almost entirely, if 

 not altogether, of particles charged positively 245 (i.e., protons, alpha-particles, 

 and probably other nuclei). Several theories have been advanced for the origin 

 of this primary radiation: (1) Annihilation of matter; (2) speeding up of 

 stripped atoms in outer space either by electrical fields or by changing magnetic 

 fields; (3) from some activity in stars in distant space; or even (4) that it is 

 radiation remaining from the original explosion some 10 9 — 10 10 years ago 

 when the present known universe was started. These assumptions are based 

 upon the theory that this radiation comes from the cosmos or outer space. 

 Some 24,i present arguments for the sun as the source of the cosmic rays and 

 argue that the magnetic field of the sun traps at least a part of the radiation 

 from the sun, which give the results as now found on the earth. There are 

 seemingly very great difficulties to explain away in establishing any one of 

 these theories. 



Owing to the effect of the earth's magnetic field there is less of this energy 

 that reaches even the outer atmosphere at or near the magnetic equator than in 

 higher latitudes, the lower-energy particles being screened off by the strong 

 magnetic fields of the earth near the magnetic equator. The energy of the 

 cosmic-ray particles that strike the upper atmosphere extends from about 10 9 

 to 10 17 ev, or even higher, with a maximum number for about 6x 10 9 ev. The 

 average energy of all particles entering the atmosphere at the equator is about 

 3 X 10 10 ev and for geomagnetic latitudes above about 40 the average is about 

 6xl0 9 ev. 



In Tables 794 and 797 are given some data on the primary radiation reaching 

 the outer atmosphere for different geomagnetic latitudes. 



2,4 Rev. Mod. Phys., vol. 21, p. 1, 1949; Stranathan, The "particle" of modern physics, 

 D. Blakiston Co. ; Montgomery, D. J. X., Cosmic ray physics, Princeton University Press ; 

 Johnson, T. R., Rev. Mod. Phys., vol. 10, p. 193, 1938; Swann, W. F. G., Reports on prog- 

 ress in physics, vol. 10, p. 1, 1946. 



246 Korff, Physics Today, vol. 3, p. 9, 1950. 



246 Teller, Edward, Physics Today, vol. 2, p. 6, 1949. 



TABLE 794.— PROBABLE CHARACTERISTICS OF COSMIC RAYS FALLING 



UPON THE TOP OF THE ATMOSPHERE AT VARIOUS 



MAGNETIC LATITUDES 



All energies are given in electron volts. 



Geomagnetic latitude 



3° 39° 52° 



Energy falling per sec un each cm 2 of the atmosphere. . 1X10 9 1.7X10° 3.2X10 8 

 Total number of ions formed per sec below each cm 2 



of the upper surface of the atmosphere 3X10 7 5.4X10 7 7.4 X10 7 



Low energy limit of oncoming particles imposed by the 



earth's magnetic field 15X10" 8X10° 2X10° 



Average energy per particle striking the atmosphere. . 3X10 10 1.6X10 10 .88X10 10 

 Probable number of particles striking each cm 2 of outer 



surface of the atmosphere per min 1.9 6.5 21.8 



SMITHSONIAN PHYSICAL TABLES 



