Radiochemical versus instrumental procedures

In radiochemical neutron activation analysis (RNAA), separations are applied in instrumental neutron activation analysis (INAA) no chemistry is involved - samples are irradiated and counted over a period of time to obtain the desired information about the elements of interest. For most elements, spectral interference-free gamma rays are available and where there are two isotopic species at the same energy, their contribution can generally be computed. 

When a radioisotope is separated from an activated sample (for example by solvent extraction, distillation, precipitation, or adsorption on inorganic ion exchangers or ion-ex-ohange resins) it can be counted using a simple, cheap beta or gamma counter in other instances, more sophisticated measurement systems are needed. 

For simple gamma counting, thallium-activated sodium iodide [Nal(TI)] scintillation detectors, which became commercially available in the early 1950s, continue to render excellent sen/ices. In spite of the introduction of many other scintillation materials, they remained preeminent. Nal(TI) detectors can be manufactured in various sizes and shapes 

For truly multielement determinations, increased selectivity is required. It is offered by semiconductor detectors, e.g., by lithium-drifted germanium [Ge(Li)] or intrinsic germanium (high-purity) [HP-Ge] types with a resolution - full width at half maximum or FWHM 

The large amount of data generated with Ge(Li) or HP-Ge radiation detector systems makes it very useful to have a computer for information processing. The equipment can be programmed to compare the areas of specified peaks in the spectra of samples and standards and, thus, to calculate the elemental levels. For additional information, the reader is referred to publications focusing on analysis of gamma spectra and reduction of data (Harpers, 1986 Op de Beeck and Hoste, 1976 Perlman, 1981 and Yule, 1981). 

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