Flow scintillation detectors

Figure 8. Photograph of the fully automated total Tc analyzer instrument in the laboratory. The labeled components are (A) robotic autosampler (B) microwave digestion unit (C) fluid handling components for sample injection, automated standard addition, sample acidification/digestion (D) separation fluidics including syringe pumps, flow reversal, and diversion valves (E) separation column (F) flow scintillation detector and (G) control computer with automation software. Reproduced with permission from the Handbook of Radioactivity Analysis, Second Edition Chapter 14, page 1152. Copyright...

Arrival of ions, which have a positive or negative charge, causes an electric current to flow either directly (Faraday cup) or indirectly (electron multiplier and scintillator detectors). 

Figure 8.28 shows how the X-rays fall on the solid or liquid sample which then emits X-ray fluorescence in the region 0.2-20 A. The fluorescence is dispersed by a flat crystal, often of lithium fluoride, which acts as a diffraction grating (rather like the quartz crystal in the X-ray monochromator in Figure 8.3). The fluorescence may be detected by a scintillation counter, a semiconductor detector or a gas flow proportional detector in which the X-rays ionize a gas such as argon and the resulting ions are counted.

The conditions for Pu reduction and elution were examined in detail, and a variety of reducing agents were tested.82 A flow system with an on-line scintillation detector was used to show the elution behavior in detail under well-controlled flow conditions. It was found that reduction and elution with hydroquinone was slow, resulting in broad tailing peaks and incomplete reduction. Some Pu remained in the Pu(IV) state and could be eluted with a complexant on completion of the reductant/HCl elution step. However, by choosing other reductants, rapid reduction and clean elution as a sharp peak could be obtained. These results are shown in Figure 9.14. 

Kynurenine was separated from L-3-hydroxykynurenine by chromatography on a Waters /uBondapak Qg column (8 mm X 100 mm, 10-/i,m), using a flow rate of 3 mL/min. The mobile phase was 0.02 M sodium acetate (pH 5.5) containing 2% methanol. Radioactivity was quantitated with a flow-through detector, using scintillation fluid at 3 mL/min. 

Urate and allantoin were separated on a /uBondapack CI8 column (3.9 mm x 300 mm). The mobile phase was 50 mM ammonium phosphate (pH 3.0). The effluent was monitored at 290 nm for quantification of uric acid or at 218 nm for detection of allantoin, or mixed in-line with scintillation fluid for quantitation by a flow-through detector. 

Radioactive tracer techniques have long been used to study particle motion in solids fluidization systems. The advantage of this technique is that the flow field is not disturbed by the measurement facility and, therefore, the measurement of the motion of the tracers represents the actual movement of particles in the system. The tracer particles are usually made of gamma-emitting radioisotopes, and their gamma radiation is measured directly by scintillation detectors. Factors that affect gamma radiation measurement were identified as the characteristics of the radiation source, interactions of gamma rays with matter, the tracer s position relative to the detector, detector efficiency, and dead time of the measurement system. 

The Berthold radioactivity monitor (produced by Laboratorium Prof. Dr. Berthold, D-7547, Wildbad 1, Calmbacher Strasse 22) is the only on-line radiometric scintillation detection system suitable for HPLC that is commercially available. The monitor is offered with cells for heterogeneous scintillation counting or as pert of a homogeneous scintillation detector system. Flow cells filled with glass... 

The term radiometric analysis is often used in a broad sense to include all methods of determination of concentrations using radioactive tracers. In a more restricted sense it refers to a specific analytical method which is based on a two-phase titration in the presence of a radioactive isotope. The endpoint of the titration is indicated by the disappearance of the radioisotope from one of the phases. Figure 9.4 illustrates two cases, (a) the determination of Ag in a solution by titration with Nal solution containing ( y t 1.57x10 y),and (b) the determination of Fe in an aqueous solution, to which trace amounts of radioactive Fe (EC 2.73 y) has been added. In case (a) the Agl precipitate is radioactive but the solution has little radioactivity until all the Ag has been precipitated. The activity of the solution is measured by a liquid flow GM-detector (Ch. 8). In the latter case (b) a two-phase liquid-liquid analytical technique is used ( 9.2.6) the titrant contains a substance (oxine) which extracts Fe(II) from the aqueous to the chloroform phase. The radioactivity of the organic phase is followed by liquid scintillation (sampling) to determine the end point of the titration. 

A flow-through scintillation detector equipped with a lithium glass solid scintillator flow cell is used to detect the eluted "Tc. The glass scintillator enables an absolute detection efficiency of 55% and is stable in the 8 mol/l nitric acid medium for pertechnetate elution. 

HPLC. Separation of lipids was carried out on a HPLC (Waters Associates, Milford, MA), using a UV detector (Waters 2487) at 205 nm and a flow scintillation analyzer (150TR, Packard Instruments, Downers Grove, IL) to de-... 

The purified pertechnetate eluted from the column was detected and quantified with a flow through scintillation detector using a lithium glass solid scintillator. This scintillator material exhibited excellent stability in the strong nitric acid solutions used for pertechnetate elution. 

Detection of the x-rays is provided by the flow proportional counter or the scintillation detector. Both types of detectors convert each detected x-ray photon into a pulse of electrical charge. The magnitude of the charge pulse is proportional to the energy of the x-ray photon and inversely proportional to the wavelength. 

The escape peaks for the Si(Li) detector are generated by the same mechanism as in the gas-flow proportional counter and the NaI(Tl) scintillation detector. Section 4.2.3 should be consulted for a more detailed description of this mechanism. The Si(Li) detector has two important differences. First, since the detector is composed primarily of silicon, it is the escape of the silicon K x-rays that causes the escape peaks in the spectrum. Second, the pulse height spectrum is used for elemental analysis and usually contains a large number of lines. Each of these parent lines will have an escape peak associated with it. The escape peak from an element with high concentration can interfere with the analysis of trace amounts of an element of lower atomic number. 

Some manufacturers utilize a tandem detector arrangement in which the fluorescent x-rays must pass through the flow counter before impinging upon the scintillation detector. In this manner, a higher detection efficiency is achieved over the entire wavelength spectrum. 

In many tracer applications it is not necessary to measure the absolute concentration of the tracer in a sample or in a material flow. In such cases a scintillation detector accompanied by a single-channel pulse height analyzer is a sufficient device. 

Figure 1 Homogeneous measuring system (1 - column, 2 - UV detector, 3 - pump, 4 - scintillator, 5 - mixing chamber, 6 - flow cell, 7 - fraction collector, 8 - scintillation detector, 9 - recording device).

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