186 ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 7 



the main gamma rays are listed for the natural radioactive isotopes. In a 

 few instances in which a very short-lived metastable state has been identified 

 as the daughter of the isotope in question, the gamma rays of the daughter 

 may be listed for both parent and daughter. 



When a semicolon is used, it means that the values listed on each side of it 

 are independent determinations of the same item, e.g., independent deter- 

 minations of the half-life or of the energy of the radiation of a radioactivity. 

 In another usage the semicolon separates the symbols in the "type of radia- 

 tion" columns when there is more than one type of decay (/?""", (3 + , a, K, or 

 I.T.) for the radioactivity. 



The observed nuclear reactions (giving the target element, projectile, and 

 outgoing particle, in order) by which the radioactive isotopes are formed are 

 listed in the last column (p = proton, n = neutron, a = alpha particle, 

 d = deuteron, / = tritium or triton (H 3 ), y = gamma ray, e~ = electron). 

 In cases in which the target material is not the naturally occurring element, 

 but one enriched or depleted in a particular isotope, that isotope is indicated. 

 No means for identifying the source or energy of the projectile is given. For 

 example, deuterons varying from low energies to 200 Mev have been used. 

 In many cases, with high-energy projectiles, multiple particles are ejected. 

 A reaction such as (d-ap2n) is a formal presentation showing what the out- 

 going particles might be and does not mean that the order of leaving the 

 nucleus was determined nor that the a, p, and n were identified. 



In some cases where the path for reaching the product nucleus can even 

 less definitely be stated the reaction is presented in the form (d-3zl0a) where 

 "$z" indicates that the product nucleus is lower in atomic number than the 

 compound nucleus by three units and "10a" means that it is lower in mass 

 number by 10 units. Where the same isotope has been made by spallation of 

 various target elements with high-energy particles, this is indicated by the 

 symbol "spal." followed by the symbols for the target elements. 



Stable product nuclei which have been identified by means of the mass 

 spectrograph are indicated by "m.s." The neutron-induced fission reactions 

 of the heavy elements are designated by such symbols as XJ-n, Th-n, Pu-w, 

 and Pa-w, while the gamma ray, deuteron, and alpha-particle-induced fission 

 reactions are designated by symbols such as U-y, XJ-d, and XJ-a. Usually, 

 but not always, "U-w" will mean the slow neutron fission of U 235 while 

 "U-d" or "U-a" designated fission products arise from U 238 . In this last 

 column the method of production for each radioactive fission product is 

 described by these symbols (XJ-n, etc.) together with the designation of its 

 radioactive parent and its radioactive daughter when these are known. 

 Similarly, for the radioactivities of the heavy natural and artificial families 

 there are listed the immediate parent and daughter isotopes. The natural 

 radioactivities without parents are listed as produced by a "natural source." 



