In the field, the distribution coefficient, Kd, for the sorption of a radionuclide by the soil cannot be expected to be constant. Even in a well defined soil horizon, Kd will vary stochastically in horizontal as well as in vertical direction around a mean value. The horizontal random variability of Kd produce a pronounced tailing effect in the concentration depth profile of a fallout radionuclide, much less is known on the corresponding effect of the vertical random variability. To analyze this effect theoretically, the classical convection-dispersion model in combination with the random-walk particle method was applied. The concentration depth profile of a radionuclide was calculated one year after deposition assuming (1) constant values of the pore water velocity, the diffusion/dispersion coefficient, and the distribution coefficient (Kd = 100 cm3.g-1), and (2) exhibiting a vertical variability for Kd according to a log-normal distribution with a geometric mean of 100 cm3.g-1 and a coefficient of variation of CV = 0.53. The results show that these two concentration depth profiles are only slightly different, the location of the peak is shifted somewhat upwards, and the dispersion of the concentration depth profile is slightly larger. A substantial tailing effect of the concentration depth profile is not perceivable. Especially with respect to the location of the peak, a very good approximation of the concentration depth profile is obtained if the arithmetic mean of the Kd-values (Kd = 113 cm3.g-1) and a slightly increased dispersion coefficient are used in the analytical solution of the classical convection-dispersion equation with constant Kd. The evaluation of the observed concentration depth profile with the analytical solution of the classical convection-dispersion equation with constant parameters will, within the usual experimental limits, hardly reveal the presence of a log-normal random distribution of Kd in the vertical direction in contrast to the horizontal direction.
The distribution coefficients Kd for the sorption of95mTc by peat as well as the corresponding rates of sorption and desorption were determined as a function of the concentration of the supporting electrolyte (CaCl2), the amount of dissolved oxygen and the pH of the solution. The results show that the Kd-values of Tc (added as Tc(VII)-pertechnetate) increase, if the concentration of CaCl2 or the amount of dissolved oxygen is decreased. The sorption was reversible with respect to the replacement of Tc by a CaCl2 solution. The half-times for the rates of sorption and desorption depend on the concentration of CaCl2 and dissolved oxygen and were in the range of 20–60 minutes and 500–900 minutes for the sorption and desorption processes, respectively.
A simple procedure for the determination of90Sr in environmental samples is described. The method uses the different solubilities of the oxalates of calcium and strontium in presence of a large excess of calcium. For this reason the method is especially suited for Ca-rich samples, as e.g., bones or soils. However, after addition of supplementary calcium it works equally well for other types of samples. The method was tested by analyzing the IAEA Certified Reference Materials soil, animal bone and algae.
Distribution coefficients Kd for the sorption of Cs and Sr on mixtures of a clay mineral (Ca-saturated bentonite) and humic material (Ca-humate) have been measured and were compared with calculated values obtained from the Kd-values observed for the pure components. The concentration of Sr and Cs in the solution was varied between 1·10–6 and 0.01N and the distribution of the elements determined by using radioactive tracers. All experiments were carried out in pure water as well as in the presence of a supporting electrolyte (0.01N CaCl2). It was found that the differences between the observed and calculated Kd-values were, if present, always negative if Cs was sorbed, and positive if Sr was sorbed.
and241Am from the global fallout in environmental and biological samples. The radiochemical recovery was for human livers Pu: 60–70%, Am: 40–60%; Bran: Pu: 50–70%, Am: 30–40%; Soil: Pu: 50–80%, Am: 30–50%. The resolution of the alpha-spectrum was for soils 30–40 keV and for livers and brans 40–60 KeV. To facilitate the wet ashing of large amounts of bran (15 kg), which are necessary to determine the presently very small activity concentrations of the transuranic elements in these types of samples, a fermentation process was employed. The procedure was tested by using NBS standard reference material and subsequently applied for the determination of Pu and Am from the global fallout in livers, plant tissues (bran), and soils.
A radiochemical procedure is described for the simultaneous determination of238Pu,239+240Pu,241Pu,241Am,242Cm,244Cm,89Sr, and90Sr in vegetation samples. The method was applied for the determination of these, radionuclides in grass, collected near Munich after the fallout from the reactor accident at Chernobyl, USSR. The specific activities observed were (in Bq kg–1 dry weight):238Pu, 0.077;239+240Pu, 0.15;241Pu, 3.9;241Am, 0.031;242Cm, 3.0;244Cm, 0.008;89Sr, 2000;90Sr, 99.
A radiochemical separation procedure has been developed for a very efficient isolation of plutonium from environmental samples. Essentially, the method involves the following steps: ashing of the sample and preparation of the load solution; separation of plutonium by a column containing a commercially available, highly specific, supported extractant; electrodeposition of Pu and subsequent -spectrometry. Detailed procedures are reported for liver samples and for soil. The modifications necessary for sample sizes above 5 g dry weight and up to 200 g are also given. Recoveries of added tracers are 60–70%. The precision of the method is <10% (RSD). The accuracy was examined by analyzing also certified standard reference materials. Due to the very efficient isolation of Pu, the resulting -spectrum is virtually free of interfering -emitters of Th and U.
A radiochemical procedure is given for the simultaneous determination of low levels of129I, actinides (Pu, Am, Cm) and90Sr in vegetation samples. It is shown that grass samples up to 5 kg fresh weight can be wet ashed conveniently by hydrogen peroxide under alkaline conditions, subsequent to an initial enzymatic disintegration. After purification of the iodine fraction,129I is determined by neutron activation analysis. Using alpha spectrometry,238Pu and239,240Pu are determined in the plutonium fraction, and241Am,242Cm, and244Cm in the americium/curium fraction. The90Sr is determined after separation by beta counting its decay product90Y.
A simple radiochemical procedure is described for the determination of90Sr in brines, which are very highly concentrated in sodium, calcium, potassium, magnesium, chloride and sulfate ions. The method is based on the different solubility of yttrium as compared to that of strontium, calcium and magnesium in ammonium chloride solutions, and utilizes Eichroms resin TRU·Spec for the purification of the yttrium fraction. The overall time required for the90Sr analysis (excluding the counting time) is less than one day. Because the procedure involves only rather simple steps, it is well suited for routine analyses of large sample numbers.
Authors:K. Bunzl, W. Kracke, E. Petrayev, and A. Ruchlja
239+240Pu and-when possible-also the ratio238Pu/239+240Pu was determined in the lungs and livers of 15 residents from Chernobyl-fallout contaminated areas in Byelorussia. In several cases various sections of the lungs were analyzed separately. With the exception of one person the activity concentrations of239+240Pu, were always within the range expected from the global fallout of weapon tests in the sixties and did not indicate any contribution of Chernobyl-derived plutonium.