Estimntion of Arsenic in Teeth by Activation Analysis

From time to time various analytical methods have been applied to tooth substance to establish the content of so-called trace elements such as lead and tin. " 2 Other ex-perimental work has shown that these trace elements may play an important part in the formation and preservation of teeth.3-6 As trace elements are present in very low concentrations, it has been necessary in previous investigations to use pooled material from many different subjects to provide an adequate sample for analysis by chemical, spectrographic, or colorimetric methods. The conclusions which may be drawn from such experiments are necessarily limited by the non-specific nature of the material. Radioactivation analysis is a technic by which many elements may be detected and estimated with a greater sensitivity than that of conventional analytical procedures. The essential basis of the method is that the element to be determined is made radio-active by exposing the sample to bombardment by neutrons inside a neutron reactor. The radioactivity induced in this way has properties which are characteristic of the element concerned. After suitable chemical separation of the element, if necessary, the amount of the induced radioactivity, the rate of its decay, and the energy of the associated nuclear radiations can be measured without much difficulty by instruments such as Geiger and scintillation counters. When the only stable isotope of arsenic is irradiated with thermal neutrons, an unstable isotope is produced by neutron capture. This unstable isotope decays with a half-life of 26.8 hours, with the emission of a-particles and y-rays. The activation cross-section is 4.0 barns, and the saturation activity for a pile flux of 1012 neutrons per square centimeter per second is about 2 X 1012 disintegrations per minute per gram of elemental arsenic. The reaction is represented by As " + n1->AsS63. The sensitivity of the determination is 10-9 gm. compared with the highest chem-ical sensitivity of 10-7-10-8 gm. Submicrochemical separations are avoided when inactive carrier arsenic is added to increase the total weight of arsenic present. In addition, "carriers " may be added to hold back other active atoms produced. The accuracy of the determination is limited only by the statistical error of counting