The behaviour of iodine in the environment is of interest both in relation to radioecology and human nutrition. Radiochemical techniques were used to evaluate various aspects of the behaviour of iodine in the environment. The natural iodine content of plant, water and soil samples collected from three sites was determined using preconcentration neutron activation analysis (PNAA). The effect of initial chemical speciation on the distribution of iodine between various soils, sediments and waters was evaluated using I-131 tracer. Iodide was found to adsorb more extensively than iodate, although for most of the solid/water systems examined, a substantial portion of the iodate was slowly reduced to iodide. Experiments involving gamma irradiation suggest that much of the sorption of iodide and reduction of iodate involved microbial processes. Distribution coefficients measured using I-131 were comparable with values based on the natural I-127 content.
A method for quench correction of samples with double radioactive labelling is described. Each nuclide makes a contribution
to the counting rate of three channels of a liquid scintillation counter. This channel overlap is an essential requirement
of the calibration procedure rather than a limitation, and allows more freedom in the choice of counting conditions. After
calibration with suitable standards the method will tolerate wide variations in the ratio of one isotope to the other extending
to single label samples of either isotope. This is the outstanding advantage over the channel ratio method which requires
a statistically significant counting rate for the higher energy isotope. The method takes advantage of the facilities offered
by a computer which may be on line or remote.14C and tritium are used to demonstrate the utility of the method.
Authors:C. Allen, K. O'Reilly, B. Cantor and P. Evans
Differential scanning calorimetry (DSC) combined with an entrained droplet technique  has been successfully used on a series of melt spun alloys with deliberate impurity additions to study the nucleation related aspects of secondary phase selection during solidification of dilute Al alloys. This paper illustrates how DSC is a sensitive tool for determining the effect impurities can have on the nucleation of secondary phases, and hence material properties of these alloys. Stepped cooling/isothermal holding profile DSC has also been used in preliminary investigations of the thermodynamic range of formation of the Al—Fe eutectic phases and their nucleation and growth solidification kinetics.