Sec. 7.12] RADIOACTIVITY 183 



one unit to the right and diagonally downward. The ordinate of each 

 member, actually the mass number, is represented by the vertical scale 

 2Z + Y where Z is the atomic number and Y is an integer. More detailed 

 data concerning the energies and ranges of alpha particles emitted from the 

 members of the series are given in Table 27. 



7.12. Seaborg and Perlman Table of Isotopes. 1 



The following table represents a complete list of all the artificial and 

 natural radioactive isotopes and stable isotopes, together with a number of 

 their important features covering information available by approximately 

 October, 1948, through publications, private communications, and almost all 

 of the restricted distribution reports of the U. S. Atomic Energy Commission, 

 the former "Manhattan District," U. S. Army Corps of Engineers, and the 

 corresponding offices of Great Britain and Canada. With very few excep- 

 tions, the criterion for listing a radioactive isotope has been the actual 

 observation of its radiation. A somewhat more extensive treatment of 

 fission product data available up to August, 1946, may be found in a Pluton- 

 ium Project compilation, "Nuclei formed in fission," /. Am. Chem. Soc, 68, 

 2411 (1946). 



The first column lists the atomic numbers and mass numbers of the 

 isotopes. The superscript "ra" following the mass number denotes a 

 metastable isomer of measured half-life of either a stable or unstable ground 

 state, but the isomeric transition need not have been observed. 



In the second column headed "Class" the degree of certainty of each 

 isotopic assignment is indicated with a letter according to the following code: 



A = isotope certain (mass number and element certain) 



B = isotope probable, element certain 



C = one of few isotopes, element certain 



D = element certain 



E = element probable 



F = insufficient evidence 



In most cases the class is determined by evaluating the uniqueness of the 

 assignment through chemical separation, reaction type and yield consider- 

 ations, genetic relationships, and type of radiation. In a few cases newer 

 techniques have been used. The term "m.s." in the second column refers 

 to the identification of the mass number by means of a mass spectrograph, 



1 The table of isotopes presented on pp. 187-207 is reprinted from Rev. Med. Phys., 20, 

 585 (1949) by permission of Professors G. T. Seaborg and I. Perlman and the publisher. 

 It was found necessary in the interest of keeping the present volume within reasonable 

 size to omit the exhaustive list of references contained in the original table. Aside from 

 this omission, however, the table is complete in all other details. The explanatory text 

 on this and the succeeding pages is also printed verbatim, except for deleted references 

 and acknowledgments, from the same publication. 



