Radiometric Determination of the Coverage

Techniques have been developed [38—42] in recent years for the study of the adsorption of radioactive substance from the solution. The adsorption of radioactive species is determined on metallized Geiger-tube windows while the tube is immersed in the electrolyte. The total recorded count is the sum of the count of the adsorbed species and of the background and solution. The latter contribution is equal to the observed count at sufficiently positive potentials where adsorption is negligible. The correction for the solution count limits the applicability of the technique described to bulk concentrations of radioactive fuel of about 10 M. The saturation coverage cannot be found experimentally in many systems. 

In contrast to the coverage determined by anodic pulses or by cathodic hydrogen deposition, the radiometric measurements yield the regular coverage 0 since the count from the adsorbed species is proportional to the adsorbed amount in M/cm. The radiometric data do not allow a direct decision if a dehydrogenation occurs during the adsorption process, since only is obtainable if j types of carbonaceous species j 

Curve c in Fig. 45 represents the coverage determined [42] radio-metrically on platinum at 10 M as a function of U. The window of the Geiger tube consisted of a polyester film with a thickness of 10 cm, a vapor deposited gold film of about 1000 A on top of the 

Curves c and b differ considerably in the location of the maximum. The difference was attributed [42] to insufficient time of adsorption. Although the insufficient time of adsorption is a valid objection [13] against the acceptance of curve b as representative for steady-state coverage, the marked difference between curve c on the one hand and curves b and a on the other hand cannot be resolved in this way. An 

The reason for the different results of electrochemical and radio-metric measurements is not known at present. Simultaneous electrochemical and radiometric determination of the coverage with carbonaceous species might give the answer. The rough agreement between the maximum of the 0 value of curve c with that of curve a is just a consequence of the estimate of the saturation coverage. There is no experimental evidence that the maximum possible coverage with methanol molecules (not with COOH and HCO) as derived by visual examination of closely packed Fischer-Hirschfelder-Taylor atomic models is achieved in practice. 

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