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  • Author or Editor: G. Evans x
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Abstract  

As part of a larger occupational exposure study in which the concentrations of 18 elements were measured in head hair and toenail collected from steel plant workers, a number of factors associated with interpreting the data obtained were examined. In this paper, some of the limitations and complications associated with hair and nail analysis that were thereby recognised are discussed. Data obtained from the occupational study demonstrated the potential for misinterpreting hair or nail analysis data either through describing results averaged over a group by arithmetic instead of geometric means or through not accounting for the age range of subjects in groups to be compared. Examples that arose from the study indicated that differences between hair from the same subjects grown at different times can both complicate and assist in interpreting hair analysis results. In an investigation into the addition and removal of metallic powders, it was found that both hair and nail can directly incorporate elements through contact with dust.

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Abstract  

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.

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Abstract  

Radiochemical methods are quite suitable for studying the behaviour of radioiodine under the dilute conditions relevant to nuclear reactor accidents. Species selective adsorbents are able to distinguish between various inorganic and organic gas-phase iodine species. A solvent extraction procedure for determining aqueous phase organic iodide, free iodine, I and IO 3 fractions has been investigated and found to be valuable, although large inaccuracies in the separation of I and IO 3 can occur for solutions of pH above 10. The extraction of potentially-volatile species in the aqueous phase gives a measure of iodine species volatility consistent with observed values of the partition coefficient. Indirect measurement suggest that the partition coefficient of HOI at room temperature exceeds 30,000.

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Abstract  

The effect of organic compounds on the production of volatile species of iodine was examined. The first step has been to identify candidates for detailed study through a series of scoping experiments, in which the chemical environment existing in CANDU reactor containment is simulated. These experiments have involved the irradiation of 10–5M CsI solutions labelled with131I containing a dilute concentration of a particular organic compound (8.5·10–3 to 1.4·10–1M). A total of 20 compounds and polymers have been tested to date. Results have shown that many of these compounds do enhance iodine volatility, and that the degree of volatility is related to system pH. Using the iodine partition coefficient (H=iodine concentration in the liquid phase/iodine concentration in the gas phase) as a basis, values as low as 300 have been observed for chloroform solutions. Conversely some compounds, such as phenol, have produced low volatility, with values of 1·105. As a reference, a partition coefficient of 104 has often been used in safety analysis.

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Abstract  

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.

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Abstract  

In the light of the remarkable strides in radioactivation analysis methods and techniques that haved been achieved progressively in the 34 years since Modem Trends conferences began, some speculations on the future directions that the field might take in the foresceable future seem appropriate at MTAA-9. Together with improvements that will likely occur in instrumentation, in prompt and ion-beam methods, there would seem to be yet a further potential for extending the range of information that radioanalytical techniques can provide by complementing RAA measurements on samples with an increased use of manipulative chemistry. Among complementary chemical methods are not only pre-activation chemistry for speciation studies and matrix removal but also, radiotracer/INAA combinations, isotopic exchange/INAA (as illustrated in this paper through recent studies on the behavior in the environment of solid waste residues), substoichiometric-RAA and classical radiochemical, post-activation separations for specific element(s). Results are presented on the toxic element content of solid waste ashes by INAA and on their uptake of65Zn and109Cd in which there is evidence of two interaction processes between waste particles and simulated groundwater: a rapid exchange (within a few minutes) and slow exchange extending over days. This tends to confirm results on leachability of toxic elements from solid wastes but serves to distinguish adsorption processes from isotopic exchange.

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Abstract  

An understanding of radioiodine volatility is important in relation to nuclear reactor safety. In this paper, findings of an ongoing experimental assessment of radioiodine partitioning are described. Radiochemical methods of determining liquid and gas phase speciation are presented along with experimental results demonstrating the validity of these methods. These results also indicate that the majority of the gaseous organic iodides detected at TMI-2 following the accident were in a low molecular weight form such as methyl iodide. It is concluded that, for 10–4 M CsI solutions, the partition coefficient increases by an order of magnitude with increasing pH and, the aqueous and gaseous concentrations of both molecular iodine and organic iodide decrease with increasing pH over the pH range of 4 to 12.

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Abstract  

The environmental impact of many postulated CANDU (Canada Deuterium Uranium) reactor accidents depends on the behaviour of iodine isotopes. In recent years a substantial portion of Canadian iodine research has focused on experiments conducted in the intermediatescale Radioiodine Test Facility (RFT) at Whiteshell Laboratories. Because of the very low concentrations relevant to reactor accidents, much of the analysis of iodine behaviour has required the high sensitivity of a radiochemical methodology. Very low gas-phase iodine concentrations (<10–10 mol/dm3) are routinely determined, up to several times an hour, using an automated airborne iodine sampler whereas various chemical forms are distinguished using selective adsorbents. Useful information regarding the chemical speciation of iodine in the aqueous phase is obtained using solvent extraction. This paper describes the radiochemical techniques used in RTF experiments, with examples of the results thereby obtained.

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Summary  

Conditional stability constants have been determined for U(IV) and U(VI) Boom Clay humic acid (BCHA) and Aldrich humic acid (AHA) complexes, under anaerobic and carbonate free conditions. The constants are needed for nuclear waste repository performance assessment purposes. The U(IV) constants were obtained by developing an approach based on the solubility product of amorphous U(OH)4. The U(VI) constants were obtained by applying the Schubert ion-exchange approach.

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Abstract  

Summertime urban PM2.5 was collected on cellulose filters in downtown Toronto, using a customized air sampler (635 l/min). Mass concentrations for up to 19 trace elements/ions were measured by ICP-AES, INAA and IC. Source apportionment was performed on these results including additional carbon and total mass concentrations using positive matrix factorization (PMF). PMF factors exhibited trends that indicated soil (18%), stationary (19%), secondary (48%), and vehicle (15%) sources. Potential source contribution function (PSCF) analysis identified probable sources of the stationary and secondary PM2.5 as originating from the south and southwest of Toronto.

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