Analysis of Contaminations in Biological Samples by Heavy Ion Scattering

In the elastic scattering of a moving ion by a stationary target nucleus, the maximum scattering angle in the laboratory reference frame is equal to, or less than, 90?? if the mass of the scattering nucleus is equal to, or less than, that of the incident ion. Thus, beams of oxygen ions incident upon a biological sample composed of only carbon, hydrogen, and oxygen will not scatter into detector placed at an angle greater than 908 . Any element heavier than oxygen scatters incident oxygen ions into such a detector. This particular choice of incident ion and detector position discriminates against the bulk of the material in a biological sample and allows detection of only the minor constituents . Accelerated beams of 20- to 30-MeV oxygen ions from the Kansas State University tandem Van de Graaff accelerator have been used in this technique. Initial studies have centered upon determining the contaminations that are present in flour. Thick targets are used, so that the beam is stopped entirely within the sample. The spectrum consists of a continuous distribution of energies up to a maximum energy corresponding to ions scattering from the surface of the sample. This maximum energy determines the mass of the contaminant nuclei, while the number of scattered particles is proportional to the quantity of contaminant nuclei.