390 ISOTOPIC TRACERS AND NUCLEAR RADIATIONS [Chap. 15 



tion; (2) identification of substances in various parts of complex systems and 

 of the routes that the tagged substances undertake and the processes they 

 undergo; and (3) determination of the rates of transfer and the quantities of 

 labeled substances in various processes and phases of a system. A partial 

 description of some of the methods that can be employed in these applications 

 is given in the following sections. 



Many species of radioactive and stable isotopes are available to qualified 

 persons and institutions from the United States Atomic Energy Commission 

 for research, medical, and industrial use. Some of the isotopes are available 

 in a variety of chemical and physical forms and at a moderate price based on 

 the cost of manufacturing and handling. All inquiries relevant to the pro- 

 curement of isotopes should be addressed to Isotopes Division, United States 

 Atomic Energy Commission, P. O Box E, Oak Ridge, Tenn. 



The available radioisotopes are listed in the Radioisotopes Catalog and Price 

 List which may be obtained from the Isotopes Division. Application for 

 any of the listed radioisotopes is made by filing with the Isotopes Division, 

 three copies of Application for Radioisotope Procurement, A. E. C.form 313. 

 When the proposed use of the isotope is approved, a purchase order may be 

 sent on receipt of A uthorization for Radioisotope Procurement, A. E. C. form 

 374. Form 313 may also be used for procurement of certain organic com- 

 pounds labeled with the radioisotopes C 14 , P 32 , S 35 , I 131 , and Au 195 . Inquiries 

 concerning specifications other than those listed in the catalog, and pile- 

 irradiation of substances supplied by the applicant should be addressed to the 

 Isotopes Division prior to preparation of the final form. 



Stable isotopes that are available from the United States Atomic Energy 

 Commission are listed in the catalog Stable Isotopes or in circular E-13. 

 These isotopes are obtained by preparing the set of forms Stable Isotope 

 Request form 100. The isotopes D (and D 2 0), B 10 , and O 18 are available for 

 direct purchase, whereas all other stable species, which are separated electro- 

 magnetically, can be obtained only on loan. 



All isotopes now being sold are also being distributed without charge to 

 qualified physicians and research workers in the United States for use in 

 cancer research, diagnosis, and treatment. The physician who is planning to 

 use the isotopes must have had clinical experience with radiations and must 

 be associated with an institution that is properly equipped to handle radio- 

 isotopes. Further details on the conditions under which free isotopes are 

 allocated are contained in circulars E-35 and D-4 issued by the Isotopes 

 Division. 



15.2. Isotope Dilution. The method of isotope dilution provides a power- 

 ful but simple means of quantitative analysis in many applications where all 

 other methods fail or may be extremely difficult. Although it has its own 

 limitations and in many instances is not so convenient as standard analytical 



