ISOTOPIC TRACERS 



171 



Accelerated 



Gas enters 



Gas is ionized 



To vo 

 pump 



Ion collector 



Fig. 12-4. A magnetic field mass spectrome- 

 ter. Ionized gas is resolved by the magnetic 

 field into a spectrum of particles of different 

 sizes. 



Laboratory safety 



Most radioactive materials used as tracers are by-products of reactor 

 operations controlled by the United States Atomic Energy Commission. 

 The AEC specifies the conditions under which radioactive materials 

 may be handled. Very small quantities (/nc or fractions of /u-c) of a large 

 number of isotopes can be purchased by any citizen under a "General 

 License." Usually these amounts are so small that serious radiation danger 

 is unlikely even with somewhat careless handling. The amounts are ade- 

 quate for certain kinds of experiments, however. 



Larger amounts of isotopes, as would be used in a typical research 

 laboratory, must be procured under a special license granted to the labora- 

 tory by the AEC. The license specifies the kinds and amounts of isotopes 

 that can be held in the laboratory at any one time. One person is usually 



