74 BELL SYSTEM TECHNICAL JOURNAL 



X, which is called the disintegration constant, and is often specified 

 instead of r or T. 



The values of the half-period T for the various radioactive substances 

 are collated in the accompanying Table, which contains also the names 

 of the substances, their usual symbols (those used in Fig.l), the sym- 

 bols embodying their atomic numbers proposed by Kovarik and 

 McKeehan, and the types of particle which they emit from their 

 nuclei. 



SYMBOLS, NAMES AND HALF-PERIODS OF THE 

 RADIOACTIVE SUBSTANCES 



The first column of this Table contains the usual symbols for the substances; the 

 third, their usual names; the fourth, their half-periods as collated by A. F. Kovarik 

 and L. W. McKeehan (/. c. supra); the fifth, the nature of the particles which they 

 emit at transmutation. In the second column, the symbols proposed by Kovarik and 

 McKeehan are given; each is composed of the atomic number of the substance, of a 

 symbol denoting the series to which it belongs, and sometimes of a second numeral 

 which, when the substance is an isotope of one or more others in the same series, 

 denotes whether it is the first, second or third of these isotopes reached in the course 

 of the transmutations. In cases of branching, the less common of the two resulting 

 substances is italicized. The annotation est. signifies that the half-periods in question 

 are estimated by extrapolating the Geiger-Nuttall relation {v.i.). The abbreviations 

 s, m, d, a stand for second, minute, day, year. 



Uranium-Radium Series: 



UI 92UI Uranium 1 4.6-10% a 



UXi 90UI Uranium Xi 24.5d 13 to UX2, ^ to UZ 



UX2 91U Uranium X2.., 1.138m 



UZ 91 Ua Uranium Z 6.69h 



UII 92UII Uranium II L2 • lO^a (est.) a 



lo 90Ra Ionium 7.43 • 10% a 



Ra 88Ra Radium 1.69 • 10% a 



Rn 86Ra Radon, radium emana- 

 tion 3.810i a 



RaA 84RaI Radium A 3.0m a 



RaB 82RaI Radium B 26.Sm j8 



RaC 83RaI Radium C 19.5ot /3 to RaC, a to RaC" 



RaC 84RaII Radium C lO^''^ a 



RaC" 8lRa Radium C" L32m 



RaD 82RaII Radium D 16a /3 



RaE 83RaII Radium E 4.85(i 



RaF 84RaIII Radium F, polonium .... 136. 3c^ a 



RaG 82 Rail I Radium G, radium lead apparently stable 



Thorium Series: 



Th 90ThI Thorium 1.3-10'% a 



MsThl 88ThI Mesothorium 1 6.7a /3 



MsTh2 89Th Mesothorium 2 6.20A /8 



RdTh 90ThII Radiothorium 1.90a or 



ThX 88ThII Thorium X 3.6U a 



