Introduction

To investigate an actinide or other alpha-emitter at the low concentrations encountered in many environmental samples necessitates chemical separation of the actinide of interest from the bulk matrix, purification by the elimination of other interferants, mounting onto suitable substrates for counting, and quantification by radiometric, mass spectrometric or other means.



Background:

• The actinide series of the periodic table comprises the naturally-occurring thorium, protactinium and uranium nuclides, and the transuranium elements neptunium to lawrencium, inclusive.

• Small traces of naturally-produced transuranium nuclides remain or are being generated in nature, but the overwhelming ‘weight’ of present environmental inventories of these elements derive from human activities, related mainly to the nuclear fuel and to military applications.

The Need for Radiochemical Procedures:

• Although direct quantitative measurement of some of these nuclides is possible by non-destructive techniques such as gamma and X-ray spectrometry, most of them decay by the emission of alpha or beta particles.

• For these nuclides, direct measurement in the presence of the host matrix (e.g water, soil) is not possible, as the particles emitted are rapidly absorbed by the matrix before they can be detected.

• At environmental levels, even those nuclides with gamma and X-ray emissions may be difficult to detect, given the minute concentrations involved, the comparatively low sensitivity of gamma and X-ray detection systems, and interference from other photon-emitters in the sample.

• In such cases, radiochemical separation of the nuclides of interest from the bulk matrix, purification by the elimination of other interferants and preparation in a form suitable for counting is essential.

• Accurate determination of actinide concentrations at these low levels depends heavily on the analyst's ability to prepare extremely pure analytes, free of any gravimetric or radiometric interferences which could lead to complications in the interpretation of the measured spectra.

• Since most of the actinides spontaneously decay by alpha-emission, high-resolution alpha spectrometry has become the most widely used technique for the determination of these nuclides.

• Over the years, numerous radiochemical separation schemes, based primarily on coprecipitation, ion exchange or solvent extraction, have been proposed and adapted for different matrices and types of analysis.

Information provided by: http://www.ucd.ie