Scintillation detectors components

The concrete block walls of the cell housing the generator tube and associated components are 1.7 meters thick. The facility also includes a Kaman Nuclear dual-axis rotator assembly for simultaneous transfer and irradiation of reference and unknown sample, and a dual Na iodide (Nal) scintillation detector system designed for simultaneous counting of activated samples. Automatic transfer of samples between load station to the rotator assembly in front of the target, and back to the count station, is accomplished pneumatically by means of two 1.2cm (i.d.) polyethylene tubes which loop down at both ends of the system and pass underneath the concrete shielding thru a pipe duct. Total one-way traverse distance for the samples is approx 9 meters. In performing quantitative analysis for a particular element by neutron activation, the usual approach is to compare the count rates of an unknown sample with that of a reference standard of known compn irradiated under identical conditions... 

Radioisotope detection of P, 14C, and Tc was reported by Kaniansky et al. (7,8) for isotachophoresis. In their work, isotachophoretic separations were performed using fluorinated ethylene-propylene copolymer capillary tubing (300 pm internal diameter) and either a Geiger-Mueller tube or a plastic scintillator/photomultiplier tube combination to detect emitted fi particles. One of their reported detection schemes involved passing the radiolabeled sample components directly through a plastic scintillator. Detector efficiency for 14C-labeled molecules was reported to be 13-15%, and a minimum detection limit of 0.44 nCi was reported for a 212 nL cell volume. 

The basic components and operating principle of a scintillation detector are illustrated in Fig. 5.26. 

A brief description of other components of scintillation detectors (generally applicable to liquid scintillators also) is given below. 

Other Components and Techniques. Other components of a liquid scintillator detector include (1) electronics, (2) a photomultiplier tube, (3) a preamplifier, and (4) a pulse-height analyzer. Description of these components and discussion of relevant topics such as (1) efficiency of scintillation counting, (2) quenching, (3) counting statistics, (4) assay optimization, and (5) radiation safety can be found in an earlier edition of this textbook. ... 

Determination of regional deposition is nsually based on measurements of particle removal from the respiratory tract after short-term steady-state breathing of radio-labeled particles relatively insoluble in body fluids. First of all, total deposition can be partitioned into extrathoracic and thoracic components by external detection of the amount of radiotracer deposited in head and neck and in thorax immediately after particle administration with a number of scintillation detectors placed around head or thorax as schematically shown in Fig. 9. Thoracic deposition can then be... 

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...

Nonetheless, it has been shown to elute immediately after the PC peak. LysoPC, if present, would elute between the PAF and sphingomyelin (Sph) peak. The latter component often shows a double peak, and this can be attributed to the separation of distinct fatty acyl species. It is well to emphasize again that compounds such as PAF and lysoPC have very low levels of unsaturated bonds present, and hence a detector other than an ultraviolet monitor would have to be used. An alternate approach would be to use tritiated PAF or tritiated lysoPC as examples and assay the eluates by liquid scintillation counting. Since the labeled compounds are at tracer dose levels, one could still assay for biological activity associated with the compounds. 

Several kinds of scintillators are available, each of them with advantages and disadvantages. This component is crucial for the quality of the whole system as a detector. Intensive research is going on in this field, with the ainl of providing good X-ray detectors for medical applications and for material testing. 

Breakdown in control and stability of the immediate detector environment with regard to cleanliness, temperature level, power supply, and radiation background interferes with reliable radiation detector operation. Electronic components function best at a cool, constant temperature in a dust-free environment. Special low-temperature and power-supply-stability controls are needed to stabilize the response of gamma-ray spectrometers and liquid scintillation systems. 

The first scintillation camera was developed by Hal O. Anger in 1958. Although this system was very crude, it contained the fundamental components of all future designs NaI(Tl) as the primary detector and weighted signals from an array of photomultiplier tubes to determine the location of detected events. Table 27.1 gives typical performance values for a modem scintillation camera. 

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