Table 850 (concluded) 647 



MATTER AND ENERGY 



mv = h/l0' 10 to h/io' 7 ; i.e., for mv ranging from 6.55 X 10"" to 6.55 X 10" 20 . According 

 to kinetic theory a H 2 molecule (;;; = 3.7 X io~ 24 ) has a v of about 2 X io 5 cm/sec. at room 

 temperature, mv is then 6.6 X I0~ 19 , within the above-mentioned range. An electron fall- 

 ing through 100 volts acquires a v of 5.9 X io 8 cm/sec. and mv= 5.3 X io~ 19 and X — 1.24 

 X io _s cm. For cathode rays of 25,000-volt velocity, X comes out 0.75 X io~ 9 cm, approxi- 

 mately. Several observers have found for diffracted electrons values of X in accordance 

 with De Broglie's relation. (Dushman, Gen. Elec. Rev., 33, 335, 1930.) 



Neutrons. — Bothe and Becker (1930) bombarded various elements with Po a particles 

 (range 3.9 cm in air, 76 cm, 0° C, initial kinetic energy 5.25 X io* electron volts). Mg, Al, 

 give trace of a resulting radiation, Li, Bo, Fe, notable effects, Be tremendous results — a 

 very penetrating radiation. Joliot and Curie-Joliot (1931) detected it through 30 cm Pb. 

 First considered photons but finally neutrons. Speed of neutrons from Be, 7 to 35 X 10" 

 cm/sec. Curie and Joliot found two groups 29 and 38 X io 8 cm/sec. Becker and Bothe 

 found Be to eject 19 photons to 1 neutron. Mass of neutron = B 77 + He 4 — N" = 1.0051 

 ±0.005 (0=i6). (Darrow, Rev. Sci. Instr., 4, 58, 1933, contains bibliography.) May 

 be considered element of atomic number ; close combination of electron and proton. 

 Effective collision radius 1.31 X io -13 cm. (Rabi, Phys. Rev., 43, 828, 1933.) 



Positron. — Positive electron (Anderson, 1932) + charge < 2e, probably exactly equal 

 to e and a mass comparable to a free negative electron. Probably results from the dis- 

 integration of atomic nuclei (in Anderson's case by cosmic rays). Out of total of 25,000 

 exposures, 1,450 cosmic ray photographs were obtained : particles of + and — charge 

 occur in about equal numbers. Energies range > io 9 volts down to few million. Mass 

 probably less than of proton. Anderson < 20 times mass of electron (Anderson, Science, 

 77, 494, 1933; Darrow, Rev. Sci. Instr., 4, 263, 1933, bibliography). 



Smithsonian Tables 



