[en] Although it is possible to understand each of the basic processes taking place in a liquid scintillation counter, the number of parameters involved, the complex way in which they interact with each other and the difficulty in assessing some of them quantitatively make it virtually impossible to give an accurate mathematical description of the complete liquid scintillation counting process. However, even imperfect mathematical models may eventually become helpful in understanding certain aspects of this process and possibly lead to improvements in measuring methods or instrument design. In recent years, various models have been proposed. The mathematical model presented in this study is a 3-dimensional extension of the model discussed earlier by one of the authors (F.E.L. ten Haaf, in Liquid Scintillation Counting, Vol.2 (eds. M.A.Crook, P.Johnson and B.Scales), Heyden, London 1972,pp.39-48). It is used to generate probability distributions representing pulse height distributions from differently quenched liquid scintillation samples. These are compared with experimentally obtained pulse height distributions. Calculated channels-ratio calibration curves, based on the pulse height distributions produced by the model, are compared with experimentally obtained channels-ratio curves. (author)

[en] Liquid scintillation counting compositions which include certain polyethoxylated poly(oxypropylene) emulsifiers allow stable dispersion of aqueous or other samples merely by shaking. Preferred are mixtures of such emulsifiers, which give homogeneous, monophasic-appearing dispersions over wide ranges of temperature and aqueous sample content. Certain of these emulsifiers, without being mixed, are of particular advantage when used in analysis of samples obtained through radioimmunoassay techniques, which are extremely difficult to disperse. Certain of these emulsifiers, also without being mixed, uniformly give homogeneous, monophasic appearing aqueous couting samples over much wider ranges of aqueous sample content and temperature than prior sample emulsifiers

[en] In the scintillation detector assembly for computerized tomography several cell chambers filled with a liquid scintillating medium are used. The medium contains a soluble fluorescent substance, like e.g. p-terphenyl, a solvent, like e.g. toluol, a compound having got a high atomic number, like lead alkyl or tin alkyl, and a substance transforming the wavelength, like dimethyl-POPO (usual scintillator fluids). (DG)

[en] The individual components of scintillation solutions and their tasks are listed. Explained briefly is the scintillation process in a liquid scintillator. Factors are discussed which influence this process as are methods applied to supress their influence. They include: ionization quenching, quenching by dilution and concentration, chemical, colour, phase and photon quenching and single-photon events causing an undesirable backgorund. (M.D.)

No abstract available

[en] Generally it is said that trace radiation measurement is achieved by increasing the counting efficiency and the amount of sample and decreasing the background counting rate. It often occurs that a detector does not operate or counting efficiency decreases considerably in internal source method, in which sample is sealed in the detector, when various conditions are not set properly. Thus the first problem is how to prepare the sample of such chemical form that does not decrease the counting efficiency. The second problem is to lower the background counting rate as far as possible, and it necessitates to adopt procedures such as coincident counting and the selection of detector and shielding materials. In the practical measurement of ³H, most examples employ emulsified or hydrophilic scintillator, while some examples adopt benzene synthesis or isotope exchange method. In the above practice, minimum measurable tritium concentration is ca. 100 p Ci/l if a water sample is measured without receiving any treatment. Isotopic enrichment is required for the samples that have less concentration than the above. (Wakatsuki, Y.)

[en] Results of a study of the scintillation yield of dioxane liquid scintillators containing solutes with different electronic affinity are reported. The chloroform and carbon tetrachloride quenching effects on these liquids are compared quantitatively. It is concluded that the solute electronic affinity has greater effect on the solvent-solute energy transfer than on the scintillation yield. (U.K.)

[en] The fluorescence quenching of four secondary liquid scintillation counters - POPOP, PBBO, α-NPO and BBO - by transition metal ions has been carried out in 40% methanol-water mixture at room temperature. The quenching is found to be appreciable and purely dynamic. The quenching rate constants were determined using the Stern-Volmer equation. The mechanism of quenching by a series of transition metal ions on these scintillation counters was studied. A reasonable linear fit of the logarithm of the bimolecular quenching constant (log k_q) with halfwave reduction potential (E_1/2) of the various metal ions was obtained. A similar correlation between the bimolecular quenching rate constant (log k_q) and the oxidation potential of the scintillation counters was also observed. These results indicate the mechanism of quenching to be electron transfer in nature, mediated by the formation of a nonemissive exciplex and the direction of electron transfer is ascertained to be from the excited fluorophore to the metal d-orbitals, The values of ΔG₀ up and down (the activation energy for the electron transfer process at ΔG=0) and the free energy at which the quenching is purely diffusion limited have been approximately estimated

[en] Selection of liquid scintillation cocktail in case of Liquid Scintillation Counting (LSC) is based on its performance of certain aspects like sample load capacity and compatibility, counting efficiency, quench resistance, figure of merit (FOM), sample stability over long period of time etc. In the present study, quench resistance of few scintillation cocktails used in our laboratory and sample stability of ³H standards prepared in the same cocktails have been studied. LSC cocktails used in the present study were commercially available: Aqua light, Ultima Gold, Quick Safe 400 and Optiphase HiSafe III. All the samples were prepared in duplicate in 20 mL glass vials. Measurements were carried out using Packard TriCarb 2900TR LSC. The quench resistance of scintillator cocktails was assessed by determining the volume of quenching agent (nitromethane) needed to reduce the counting efficiency by a factor of two (the quench half volume, V1/2)

[en] An earlier paper by the author showed that scintillation camera systems can be described effectively using the resolving times T and τ₀ of the dominant nonparalyzable and paralyzable components, that is, the detector system and the computer interface, respectively. When used with a full spectrum window, the camera has a lower nonparalyzable and an upper paralyzable operating range with normalized threshold input rate n_t=N_tτ₀=ln(1+k_Tn_t), where k_T=T/τ₀. Correct determination of T and τ₀ requires that both r₁₂ and r in the normalized two-source equations k_T=(2/r₁₂-1/r) and k₀=(r₁₂/2r²)ln(2r/r₁₂) come from the nonparalyzable (n≤n_t) and paralyzable (n≥n_t) ranges, respectively. A serious constraint of the two-source method, therefore, is that the large ratio a=n₁₂/n=2 can lead to an input rate range (n,n₁₂), which includes the threshold point n_t, and in which neither T nor τ₀ can be measured correctly. The decaying source method constitutes a refinement of the two-source method, which enables smaller ratios 1< a<2 to be used, and also includes the two-source method as a special case (a=2). This new method requires just two consecutive readings on a single decaying source, as opposed to three measurements on two sources of activity, for each determination of T or τ₀, thus also minimizing staff exposure. The fact that only count rates and time intervals need now be recorded greatly simplifies computerization of the data acquisition and analysis activities, and the potential for real-time applications is obvious. The method enables T and τ₀ to be measured accurately and with sufficient resolution to reveal possible variations with input rate. Long measurement times using a decaying source can be avoided, if required, by using a set of decaying sources simultaneously to cover different portions of the count rate range. The application of the measurement procedure in real-time and the use of the resolving times in the accurate correction of deadtime losses, also in real-time, are treated separately in another paper