Gallium Impurity Research Articles

Artificial Radioactivity as a Test for Minute Traces of Elements

The high voltage and large current of the Berkeley cyclotrons have made it possible to obtain radioactive isotopes with activities of extremely high intensities, especially when deuterons are used as the bombarding particles. It is the purpose of this note to show how this circumstance has made it possible to identify extremely small amounts of impurities by means of their characteristic half-lives, after the substance containing the impurities has been bombarded with deuterons in the cyclotron. A quantitative estimation of the amount of the impurity can be made in those cases where the yield of the reaction involving the impurity has been previously determined. In the cases where this yield is not known an estimate can be made by means of a comparison with the known yield of some reaction of the same type. As an example the detection of extremely small (1) Lawrence and Livingston , Phys . Rev., 46 , 608 (1934); Lawrence and Cooksey , ibid. 50, 1131 amounts of gallium in iron is described. Other examples are given more briefly. When a sample of iron was bombarded with deuterons it was found that two of the radioactivities produced could be ascribed to an extremely small amount of gallium impurity in the iron (six parts in one million, as will be shown later). This was established by the fact that the halflives of the two activities, 22 .min. and 14 hr. (electron emitters), were identical with the known half-lives of electron emitting Ga70 and Gall, respectively.2'3 A chemical separation according to the methods of Noyes and Bray was performed upon a sample of bombarded iron to which a small amount of carrier gallium had been added after the bombardment. The 22 min. and 14 hr. periods appeared only in the gallium fraction.