Radiometric methods

18) is similar to eq. (17.15), but the advantage is that the measurement of the relative activities AxfA is sufficient and the determination of masses is avoided. 

Many metals in amounts ranging from micro- to nanograms have been determined by isotope dilution in combination with the substoichiometric principle. Isolation of equal amounts m is usually achieved by solvent extraction of a metal chelate into an organic solvent. It must be certain that the substoichiometric amount of the chelating reagent reacts quantitatively with the metal ions in the concentration range considered. 

Radiometric analysis is also based on the use of radiotracers. However, in contrast to isotope dilution analysis, stoichiometric relations are applied in radiometric methods. The substance to be determined is brought into contact with another substance labelled with a radionuclide or containing a radionuclide. Reaction between these two substances yields a radioactive product that either can be separated and measured or can be measured continuously in the course of the reaction. The activity is proportional to the amount of substance to be determined. 

In radioreagent methods, the radioactive product of the reaction between the substance to be determined and a radioactive reagent is separated by various methods, such as precipitation or liquid-liquid extraction. For example, Cl , Br or 1 in concentrations down to 0.5 pg/1 can be determined by addition of an excess of phe-nylmercury nitrate labelled with ° Hg. The complexes formed with the halide ions are extracted into benzene, whereas the phenylmercury nitrate stays in the aqueous phase. From the difference between the activities in the aqueous phase before and 

Radiorelease methods are based on the same principle the substance to be determined is brought into contact with another substance containing a radionuchde reagent, and by their interaction a certain amount of the radionuclide is released and measured. For this method substances loaded with Kr (radioactive kryptonates), for example krypton clathrates, may be applied. By reaction with oxygen Kr is released and can be measured continuously. Oxygen dissolved in water can be measured by reaction with jj deposited on Cu 204 jj jg oxidized and released into the 

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Potassium is analyzed in chemicals that are used in the fertilizer industry and in finished fertilizers by flame photometric methods (44) or volumetric sodium tertraphenylboron methods (45) as approved by the AO AC. Gravimetric deterrnination of potassium as K2PtClg, known as the Lindo-Gladding method (46), and the wet-digestion deterrnination of potassium (47) have been declared surplus methods by the AO AC. Other methods used for control purposes and special analyses include atomic absorption spectrophotometry, inductively coupled plasma (icp) emission spectrophotometry, and a radiometric method based on measuring the radioactivity of the minute amount of the isotope present in all potassium compounds (48). 

Physical methods Physical methods include photometric absorption and fluorescence and phosphorescence inhibition, which is wrongly referred to as fluorescence quenching [1], and the detection of radioactively labelled substances by means of autoradiographic techniques, scintillation procedures or other radiometric methods. These methods are nondestructive (Chapt. 2). 

The study of carbonate complexes of Pu is complicated by various experimental difficulties. The low solubility of many carbonates (7), leaving a very dilute Pu concentration in solution, results in difficulties to the experiments with electrochemical or spectrophotometric methods. However, the radiometric method with solvent extraction or solubility measurement is easily applicable for the purpose. Unlike the solution with anions, like Cl, N03 etc., the concentration of which can be varied at a constant pH, the preparation of solutions with varying carbonate concentration accompanies indispensably the change of pH of the solution. As a result, the formation of carbonate complexes involves accordingly the hydrolysis reactions of Pu ions in solutions under investigation. It is therefore prerequisite to know the stability constants of Pu(IV) hydroxides prior to the study of its carbonate complexation. 

Unlike non-radiometric methods of analysis, uncertainty modelling in NAA is facilitated by the existence of counting statistics, although in principle an additional source of uncertainty, because this parameter is instantly available from each measurement. If the method is in a state of statistical control, and the counting statistics are small, the major source of variability additional to analytical uncertainty can be attributed to sample inhomogeneity (Becker 1993). In other words, in Equation (2.1) ... 

In magmatic processes, both parent and daughter nuclides are usually present in the solid sources, magmas and crystallizing minerals, so that (N2), which is a priori unknown, cannot be neglected. In order to solve Equation (I) for t, the age of fractionation, both terms of this equation are divided by the concentration of a stable isotope (or the activity of a long-lived isotope) of the daughter element. Such a normalization, similar to those used in other classical radiometric methods (Rb-Sr, Sm-... 

TABLE 13 Radiometric Methods of Dating Used in Archaeology ... 

ICP-MS (inductively coupled plasma mass spectrometry) is frequently used for determining ultratrace amounts of technetium [9]. In spite of the high cost of the equipment, this detection method is far superior to other radiometric methods as regards sensitivity. When a double focussing high-resolution system is used (HR-ICP-MS) and an ultrasonic nebulizer is introduced [10], the detection limit is in the order 0.002 mBq. The ICP-MS method has been successfully applied to the determination of environmental "Tc as well as to other long-lived radionuclides of neptunium and plutonium in the environment. 

Lo, J. M., Tseng, C. L., Yang, J. Y. (1986) Radiometric method for determining solubility of organic solvents in water. Anal. Chem. 58, 1596-1597. 

Radiometric methods are unique for their ability to provide directly the surface concentration of the adsorbate. A method for in situ study of electrochemical reactions on solid electrodes was invented by Joliot. ° He used a thin gold foil as an electrode which at the same time served as the window of the radiation counter. Johot determined the kinetics and the effect of tartaric acid on polonium electrodeposition on gold. The method was later further developed and improved (e.g.. Refs. 102,103). 

The second radiometric method, proposed by Kazarinov, ° is based upon a different principle. At the beginning of an experiment, the electrode is placed far from the detector, which is situated at the bottom of the cell,... 

The radiometric method is used to determine Tc in environmental water samples . The work provides a carrier-free procedure for the determination of Tc in aqueous solutions as low as 0.5 dpm/1. The chemical separation is followed by electrodeposition on a stainless-steel cathode involving determination of Tc by counting. 

Traditional exploration for sandstone-type uranium deposits has centered on genetic models and radiometric methods (Morse 1969 Harshman 1970 Rubin 1970). However, these methods have become prohibitive for sandstone-type uranium deposits hidden at a depth of hundreds of metres (Riese et al. 1978). Radioactivity detectors are ineffective in regions where there is a relatively thin inactive overburden (Bowie etal. 1970). 

Radiometric method, hydrogen peroxide determination, 655-6 Rainwater... 

Poskus and Agafonovas [483] have applied radioactive Tl-204 to study its UPD on a polycrystalline gold electrode in alkaline solutions. The potential dependence of the equilibrium surface concentration obtained from the radiometric method has been compared to that calculated from CV. Surface concentration of Tl decreased monotonically as the potential was changed from the more positive Nern-stian values. This dependence exhibited a minimum without reaching zero. At more positive potentials (with respect to the minimum), adsorption of T1+ induced by specifically adsorbed hydroxyl anions occurred. 

The American scientist B. B. Boltwood appreciated as early as 1907 that radioactive decay can tell us about the age of the Earth. The best estimate until that time was around 98 million years, which Lord Kelvin deduced in the 1860s by considering how long it would take for the hot core to cool down. Boltwood calculated that the planet could be as much as two billion years old. The current estimate of more than twice this value is supported by a host of other radiometric methods which look at the relative abundances of parent and daughter isotopes in radioactive decay chains. 

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