Thorium-234 interference measurements

The Cr 320.0-keV gamma ray has three interferences, all of different types. Nd (319.7 keV) falls under the chromium peak and the correction is monitored by the Nd 531-keV peak. Cr itself is made from the reaction Fe (n,a)Cr k Ta has intense gamma rays of 222.1 and 100.1 keV, which pile up to give a peak at 222.1 keV that is not resolved from the chromium peak. Below this in the box is shown the 311.9-keV peak of Pa by which thorium is measured. This peak has under it a peak of 310.5 keV caused by the double escape from the 1332.5-keV gamma rays of Co (1332.5-1022 keV). The example of a Compton edge correction is that of the 889.6-keV peak of Sc , which lies on the Compton edge of the 1099.2-keV gamma ray of Fe . The photopeak of the 1099.2-keV peak serves as the monitor. 

An alternative to the bridge technique was recently reported for thorium analysis in silicate rocks for which both Th and Th are measured on a single lon-counting detector (Rubin 2001). With careful chemistry and mass spectrometry, °Th/ Th ratios of igneous rocks can be measured with this technique with a precision that is similar to the bridge method. The disadvantage of this technique is that °Th ion-count rates are extremely low (around 10 cps) with normal silicate thorium ratios and are therefore subject to perturbations from background variation and low-level isobaric interferences in normal samples. 

The UVV spectrum of 32a is pH dependent In the presence of Li+ ions the spectrum of 32b shows a specific shift that allows quantation, which is carried out at 490 nm, pH 13. Possible interference by traces of heavy and transition elements is masked witii [Mg-EDTA] added to the sample. The metiiod was tested for Li" " in seawater and deproteinized plasma. f Determinations of Li in drugs and blood serum are carried out at 601 nm in alkaline solution. Originally designed for colorimetric determination of thorium in trace amounts. Measurements of tile hthium complex can be carried out over a wide range of wavelengths Determination in pharmaceuticals at 468 nm, with linear range of 0.1 to 4.0 mg analysis of blood serum at... 

Here is how SAL works Samples are received in a reception and storage room, then routed to the appropriate wet chemical analysis laboratory. There, they are analysed for uranium, thorium or plutonium content, and purified aliquots (portions of the sample) are prepared for the isotopic analysis of three elements. Isotopic analyses are performed routinely by mass spectrometry, and radiometric techniques are used for back-up. Emission spectrography serves to detect the presence of impurities which could interfere with the measurements and thus distort the results of the chemical and isotopic analysis of uranium, thorium and plutonium. Complex calculations and quality checks are performed on minicomputers, which are connected in a network to a central laboratory mini-computer. A central laboratory data system stores and provides analytical reports and enables the quality of the analyses and the status of the flow of samples through the laboratory at any time to be monitored. 

The majority of the longer-lived transuranic nuclides produced by neutron capture reactions decay primarily by a-emission. Most environmental samples contain radionuclides from the natural uranium and thorium series in concentrations often many times greater than transuranic concentrations. As a result, the chemical problems encountered in these measurements are derived from the requirement that separated trans-uranics should be free of a-emitting natural-series nuclides which would constitute a-spectrometric interferences. Table I lists those transuranic nuclides detected to date in marine environmental samples, together with some relevant nuclear properties. Their relative concentrations (on an activity basis) are indicated although the ratios may be altered by environmental fractionation processes which enrich and deplete the relative concentrations of the various transuranic elements. Alpha spectrometric measurements do not distinguish between 239p Pu, so these are... 

Table 16.1 lists all of the nuclides in the uranium and thorium decay series which one might hope to measure. The comments column lists factors which should be taken into account when setting up the analysis and the nuclide library for the task. There are many potential spectral interferences and some of the more relevant ones are listed in Tables 16.2 and 16.3 and are discussed below in Section 16.3.5. The resolution of the major interference... 

Geologists and lunar scientists now use this technique to measure not only elements like lead, uranium, thorium, rubidium, strontium, argon, and potassium, but they also now include barium and ten of the rare earths in geologic analysis. The nuclear industry measures lithium, boron, uranium, and plutonium routinely. The technique has a potential for broad application. Major and minor phases of such elements as molybdenum (55%) and rhenium (0.1%) can be determined because accuracy is possible even in the presence of major interferences. At impurity levels of 1-500 ppm almost all of the above-mentioned elements can be determined, and, in addition, such elements as magnesium, chromium, copper, silver, calcium, nickel, and cesium. ... 

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