Radiometric counting

N HC1, or (3) diluted by a factor of 20 with 0.5N HGl. The length of the plutonium band on the column was measured and the effluent solutions were analyzed for cation concentration. Plutonium in the effluent solutions was determined by radiometric counting, the americium by gamma spectroscopy, and the remaining cations by atomic absorption. 

Quantitation by mass spectrometry or radiometric counting requires reference to known standard material. This reference can be internal to the sample, wherein the reference material is added to the sample at an appropriate stage of processing, or it can be external when the response of the analyte in the sample is compared to the response measured for the reference material. A commonly employed method, isotope dilution mass spectrometry, is to add a known amount of an isotopically altered tracer (sometimes called a spike) to the sample. 

Most elements are efficiently ionized at the high temperature of the plasma. For most metals (ionization potential <8 eV), ionization is typically greater than 90%. Many elements have an ionization efficiency >98%. The few elements not analyzed by ICP/MS are H, He, C, N, O, F, Pm, Ne, Ar, Kr, and short-lived radionuclides. These exceptions have high ionization potentials, severe spectral interference, or are better measured by radiometric counting or other mass spectrometric methods. 

Internal standard Sometimes standards are not available for all the cosmogenic and SN radionuclides. Therefore, many AMS facilities have embarked on elaborate programs to manufacture their own calibrated standards. In most cases, these materials have been prepared locally with the utmost care using conventional radiometric counting, mass spectrometric methods, and/or standard gravimetric dilution techniques to establish their isotopic ratios. Alternatively, some AMS laboratories have prepared standard materials by series dilutions of primary standards. 

Analyses. Plutonium was determined radiometrically. A weighed sample of a compound was dissolved in 2M H2S0lt with a few drops of 90% HNOj to oxidize organic material, and an aliquot of this solution counted for alpha activity. 

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) ... 

The situation is quite different in the case of an acetic acid-water system. The energy of acetic acid adsorption on platinum is low and therefore the voltammetric curves taken in the absence and in the presence of acetic acid in the supporting electrolyte are nearly the same. However, radiometric data show that C-labeled acetic acid is adsorbed on the electrode surface. Most likely the acetic acid molecules are adsorbed on the top of the water molecules populating the electrode surface. Simultaneously recorded voltammetric and counting rate data are shown in Fig. 8. 

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. 

One of the radiometric techniques is precipitation with a radioactive reagent. For example, the halides can be precipitated with 110Ag, silver precipitated with 131I, the sulfates and chromates precipitated with 212Pb or 131Ba, while Al, Be, Bi, Ga, In, Th, U, Zr, and the rare-earth elements can be precipitated with 32P04. This method suffers from the lack of selectivity and the need to make careful corrections for self-absorption in counting the samples. 

The classic example of a radiometric titration concerns the titration of some unknown material with a radioactive reagent to give a radioactive precipitate. In this case, the activity of the supernatant or the precipitate can be followed as a function of titrant volume, as shown in Figure 4.10. In this type of titrations, the tracer must have a long half-life and must emit high-energy 3 or y rays so as to minimize self-absorption corrections (assuming, as is common practice, that the supernatant or precipitate is removed from the system and counted in an external sample counter after the addition of each volume of titrant). 

Both radiometric and mass spectrometric detection approaches have been used in automated radiochemical analysis, depending on the radionuclides of interest and the capabilities of the laboratory involved. The tradeoffs between radiation counting and atom counting have been described.14 16 17 Short-lived fission products may be advantageously detected with radiation detection, whereas long-lived (low specific activity) radionuclides can be determined with better sensitivity using ICP-MS. 

In this radiometric detection approach, the detection limit could be lowered by using a stopped-flow procedure that captured 89% of the eluted "Tc within a 2.5-mL flow-through counting cell. Continuous-flow and stopped-flow detector traces are... 

A tracer usually is a solution of a standardized radionuclide that is an isotope of the analyte radionuclide. With the identical chemical behavior of tracer and analyte, the yield of the tracer, determined radiometrically, represents the yield of the analyte. In this respect, the radioactive tracer has the same function as the stable carrier. Furthermore, for alpha particles of the usual 4-10 MeV energy in a thin source, the ratio of net count rate to activity is the same for the tracer and the analyte, so that the analyte activity is directly calculated from the activity of the tracer and ratio of the net count rates at the peaks of the analyte relative to the tracer, measured with an alpha-particle spectrometer. 

Methionine Sulfoxide Adsorption Check. S35-labeled methionine sulfoxide was prepared by oxidizing methionine-S35 with peroxide (6). Five microliters (ca. 20,000 counts per minute per microliter) of an aqueous solution of the sulfoxide was injected into each of 20 cockroaches. The first 10 were immediately immersed in hot 80% ethanol, and the remainder in hot 5% trichloroacetic acid to be homogenized and extracted. The extraction procedures were similar to those described above, except that precautions to prevent oxidation were not taken and the supernatant liquids, except for the acidified ethanol and ether washes, were not combined but were collected separately in 100-ml. volumetric flasks. The protein residues were hydrolyzed in 6N HC1 and, like the other fractions, were then diluted to 100 ml. with water for radiometric analysis. 

Measurement Techniques. Light isotopes Concentrations of were determined radiometrically after synthesis of propane (13) in a proportional counter after about twenty-fold electrolytical enrichment of (14), The C content of large samples (. 5 g C) were determined by liquid scintillation counting after synthesis of benzene (15) fi-om CO2 which was extracted fi-om the water sample after acidification. The C content of small samples (<0.5 g C) were measured by accelerator mass spectrometry (AMS) W the Isotrace Laboratory of the University of Toronto. The C, and isotopic... 

All radiometric assaying was performed by conventional liquid scintillation counting techniques using a Beckman LS-100 automatic scintillation counter and Ready-Solv GP scintillation solution. 

Whereas interval dating can be carried out by counting annual layers (e.g. Baldini et al., 2002), radiometric techniques are needed to provide the... 

GPC (total radioactive strontium) = beta gas proportional counter Bq = Becquerel dpm = disintegrations per minute EDTA = ethylenediamine tetraacetic acid GFAAS (total strontium) = graphite furnace atomic absorption spectroscopy ICP-AES (total strontium) = inductively coupled plasma atomic emission spectroscopy ICP-MS (isotopic strontium composition) = inductively coupled plasma-mass spectrometry LSC (isotopic quanitification of 89Srand 90Sr) = liquid scintillation counting pCi = pico curies (10-12 curies) PIXE (total strontium) = proton induced x-ray emission TMAH = tetramethylammonium hydroxide TNA (total strontium) = thermal neutron activation and radiometric measurement TRXF (total strontium) = total-reflection x-ray fluorescence... 

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