Investigation of the characteristics of a sedimentation tank by a radioactive tracer technique

The Superposltlon o f Autoradiographs and 154[icrographs using the K o d l b Dye Transfer P r o c e s s (Received 19 February 1959)

etched in Keller's reagent, were enlarged x 3.1 on to matrix films which were processed as for Fig. 1. Regions of the alloy containing chromium are shown in red; dark etching regions of the mierograph and holes in the specimen in green, hence regions which contain chromium and etch dark appear black.

A MICROGRAPHfrom a transparent specimen which Isotope Division S . M . MAKI~ has been autoradiographed using the stripping film Atomic Energ~ Research Establishment G . T . ROGERS technique{1) shows the distribution of radioactive Harwell tracer superposed on the microstructure. The References stripping film technique is not satisfactory for opaque and especially for metallic specimens(2) and therefore 1. PELe S. R., Int. J. Appl. Rad. Isotopes 1, 172 (1956). the autoradiograph and micrograph must be obtained 2. MAm~ S. M. and ROOERSG. T., A.E.R.E. Report separately. It is much easier to interpret the autoI/R. 2227. radiograph when the distribution of radiotracer is 3. Kodak Data Sheets CL 1, 2. superlx~ed on the microstructure. In the Kodak Dye Transfer Process (s) coloured images, obtained from separation negatives, are superposed to produce a coloured print. This process can be used to make a composite print showing the autoradiograph and micrograph in appropriate colours by using the autoradiograph and micrograph in place of separation negatives. Such composite Investigation o f the Characteristics o f a prints are much more easily interpreted than Sedimentat/on T=,,k by a Radioactive separate or superposed black and white prints. Tracer Tech,,;que Figs. 1 and 2 show examples of composite prints obtained by this method where the colours were (Received 24 December 1958; obtained by transferring cyan and yellow micrograph in revisedform 23 February 1959) dye images and magenta and yellow autoradiograph A R A D ~ O A ~ tracer experiment was made to deterdye images. I n Fig. 1 an autoradiograph obtained using copper- mine the throughput time and dispersion of a sample 64 as a radio-tracer shows the distribution of copper of water passing through a radial flow sedimentation tank in the Bridge of Earn sewage purification works. in an aluminium 4% copper alloy cooled from the melt at 0"35°C/min. Micrographs ×36.5 of the The tank has a capacity of 50,000 gal and discharges specimen, etched in aqueous 25% H N O s + 2°/OHF, into a tidal river not used as a source of drinking and of the autoradiograph, were contact printed water. Before the experiment, the mean throughput on to separate matrix films. Both matrices were time was estimated to be about 12 hr. Na 24 was chosen as a tracer, to avoid long-lived processed and registered according to the manufacturer's instructions. The matrices were dyed to radioactive contamination. The activity used was 100 mc to provide ultimate concentrations well below give a suitable combination of colours and the dye images transferred to paper in the usual way. Regions the maximum permissible level for drinking water (8 × 10- s #c/ml) ¢I~ even though the effluent was not of the alloy containing copper, i.e. those which were radioactive, are shown in red and dark etching into a potable water supply. The tracer was introduced in the form of sodium regions of the micrograph in green; hence regions bicarbonate (1.5 g) dissolved in 100 ml of dilute which contain copper and etch dark appear black. Fig. 2 shows the distribution of chromium in an hydrochloric acid. After the removal of 0.25 ml of aluminium 5½°/O Zn, 2½% Mg, 0.2% Cr alloy after solution for comparison purposes, the remainder was homogenization at 460°C for 25 hr. Micrographs poured into the inlet channel of the tank, just above × 7-8 of the autoradiograph and of the specimen the standing wave flume. 302

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Technical notes

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From the discharge point of the circumferential channel, 5 ml samples ofllquid were taken at intervals of half-an-hour after the injection and measured in a well-type scintillation counter. Fig. 1 shows the counting rates obtained as a function of time; vertical lines indicate the standard deviation. T h e r a t e of flow into the tank during the period of the experiment was recorded by the standing wave flume recorder. Readings at half-hour intervals are shown in Fig. 2.

from the tank, will depend on how quickly changes in the inflow are reflected as changes in the outflow--in fact on the integrating time constant of the settling tank. Fig. 1 represents the curve obtained assuming a very long time constant and Fig. 3 that with a time constant of zero. The measurements of the variations of the rate of flow were made at the inlet channel and, as a large tank would produce a great smoothing effect, the flow from the discharge point was probably

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From Fig. 1 it can be seen that none of the inserted material appeared at the discharge point of the circumferential channel until about 2 hr had elapsed from the time of insertion. Most of the radioactive solution was clear of the tank after about 14 hr, but a small residuum appeared to be leaking out very slowly. Fig. 1 does not give a completely accurate picture of the rate of output of radioactive material, because it does not take into account variations in the rate of flow of sewage through the tank. A histogram showing the total activity discharged in each halfhour period was constructed, from Figs. 1 and 2, and is shown in Fig. 3. The ordinate of Fig. 3 is in arbitrary units but the standard errors, although not plotted, are of the same order of magnitude as those shown in Fig. 1. The true curve for activity discharged

almost constant during the course of the experiment. I n the conditions of this experiment Fig. 1 is therefore likely to be nearer the true curve than Fig. 3. Fig. 1 has a typical shape for a flow curve accompanied by dlspersion, and indicates that good mixing is occurring.

Acknowledgements--The authors would like to thank Mr. J. McL. FRASER of Babtie, Shaw & Morton, Consulting Civil Engineers, Glasgow, for much helpful advice on the civil engineering aspects of the problem. Mr. J. C. LAw and other members of the staff of Perth County Council kindly provided the help needed on the site.

Regional Physics Department W~stem Regional Hospital Board Glasgow, Scotland

J . M . VALENTINE M . M . BLUHM

Reference

1. Brit. J. Radiol., Suppl. 6, 48 (1955).