Simultaneous determination of actinide nuclides in environmental materials by solvent extraction and alpha spectrometry

Abstract

Actinide analysis based on the selection of groups, instead of separation of individual elements, has been applied to monitoring and control of the increasing variety and amounts of actinide nuclides in environmental materials contaminated by controlled discharges of liquid wastes. Multi-element actinide analysis is achieved by extracting the whole group, or part of it, in the tri-n-octylphosphine oxide-n-heptane-nitric acid-sodium nitrate system, stripping into ammonium carbonate solution and electrodeposition, followed by solid-state alpha spectrometry, with unusual actinide nuclides as yield tracers. This system gives efficient separation from virtually all common elements.

Common operations for the several functions of sample dissolution, tracer exchange, solvent extraction and electrodeposition have been developed, which are suitable for the group from actinium to curium. Detailed procedures, with variations, for simultaneous measurement of these actinides are stated, in order to allow application to biological materials and radioactive effluents in two combinations, the first in valency states III, IV and VI, and the second in valency states IV and VI with valency state III eliminated. They have been fully evaluated for plutonium-239 plus-240 with plutonium-236 as tracer, and americium-241 with americium-243 as tracer, and the scope is indicated for other members of the group. Up to 2 kg of edible seaweed or 10 kg of fish flesh can be handled, with detection limits (in terms of activity to double background) of 2 × 10^–6 and 4 × 10^–7 pCi g^–1, respectively, for a 1-week counting time. Sensitivities for precision with 4 per cent. standard deviation are 4 × 10^–4 and 8 × 10^–5 pCi g^–1, respectively, which corresponds to levels associated with fallout.