Tables 639-641 

 RADIOACTIVITY 



TABLE 639. — Relative Total Ionization by a Rays in Various Gases 



(After Bragg, Taylor, Laby, Hess-Hornyak.) 



525 



TABLE 640.— Delta Rays 



Delta rays are electronic rays (j3 rays) produced by bombarding a substance with 

 a particles, an ionization of a comparatively infrequent type. 5 rays are of various 

 velocities, some corresponding to a few volts ; others have a velocity, 3 X io 9 cm/sec. 

 (2400 volts) ; the number of S rays produced by bombarding metals is of the order of 

 8 to 10 per a particle. 



The existence of swift 5 rays in hydrogen gas has been proved by Bumstead (cloud- 

 track method). From the wide column of droplets (a-ray track) there are short, narrow 

 tracks nearly at right angles. Wilson obtained similar 5-ray tracks in air near the begin- 

 ning of the a-ray tracks. These experiments show that some 5 rays are capable of ionizing 

 air along a path of considerable length. Bianu (ionization method) was able to show that 

 5 rays ionize the gas and determined the velocity of the swiftest 5 rays as 2.9 X io 9 cm/sec. 

 This velocity corresponds to 2400 volts. C. T. R. Wilson suggests that the 5 rays may be 

 due to expulsion of electrons from inner orbits of the bombarded atoms, which would agree 

 with Kapitza's observation that the average energy lost by an a particle in producing a pair 

 of ions is greater at high velocities than at low. Bianu shows that the number of low-speed 

 5 rays produced is 40 times as great as the number of high-speed 3 rays and that each a ray 

 from RaF produces, on the average, 10 of the more numerous class. His work also shows 

 the 5-ray emission to be independent of the nature of the metal bombarded, an observation 

 in agreement with earlier investigations. The usual explanation offered for the production 

 of 5 rays is that an a particle entering a substance loses energy in ionization and that some 

 of the electrons liberated possess speeds which enable them to escape. 



TABLE 641. — Heating Effect of Radium and Its Emanation 



(Rutherford and Robinson, Philosophical Magazine, 7.5, p. 312, 1913.) 



Other determinations : Hess, Wien. Ber. 121, p. 1, iqi2, Radium (alone) 252 cal. per hour per gram. Me 

 Hess, Wien. Ber. 121, p. 603, 1912, Radium in equilibrium, 132.3 gram. cal. per o hour per gram. See also, Ca 



lever and 

 »««---.j, .. .^... Mj*.> . . — • , f. "~j, -.7..., .-.uu.uii. in i.ijuiiiui .uiu] i£«.j L.1.H11. Lai. h ci n^' u » h ci ji 1 ^***. uw iii^ii, t_.allendar, 

 Phys. Soc. Proceed. 23, p. 1, 1910; Schweidler and Hess, Ion. 1, p. 161, 1909; Angstrom, Phys. ZS. 6, 685, 1905, etc. 

 Smithsonian Tables. 



