A two-way scanning method for total body in vivo neutron activation analysis

When determining the total body content of many elements by neutron activation analysis, irradiation and whole body counting by scanning along the length of the body has significant advantages. A neutron source of lower output and a whole body counter using smaller detectors and shielding (than otherwise needed) can provide a high, uniform response for many elements throughout the body. This was previously achieved by making the speed and direction of scanning identical in irradiation and counting (one-way scanning). A simple theoretical model for scanned irradiation and counting is described. The model is used to show that a scanning regime in which both scanning directions are used (two-way scanning) can provide acceptably uniform response for elements having induced activities of a wide range of half-life. This is supported by measurements made using an existing scanning facility for total body in vivo neutron activation analysis. The two-way scanning regime offers the advantages of increased patient comfort, simpler operation and more efficient use of the time available for counting induced activity.