[en] In the present experiment, an attempt is made to raise the average Z of a scintillation solution with as little attendant quenching as possible. Since high-Z atoms quench by means of a close encounter, such encounters are minimized by the use of alkyl groups substituted on the solvent, solute, and heavy atoms. The aromatic compound 1,2,4-trimethylbenzene (pseudocumene) is used as the solvent; 4,4''-di(5-tridecyl)-p-terphenyl (SC-180) as the solute; and tetrabutyltin as the high-Z material. To establish the validity of our ideas, various experiments have been performed with less protected solvents, and heavy atoms. These include benzene, toluene, p-terphenyl, bromobutane, and bromobenzene

[en] The modeling technique described was developed to aid in interpretation of the effects of various changes in scintillator formulations on the shape of scintillation pulses. Theoretical pulse shapes were synthesized, the system response function is folded in, and the result is overlaid on the raw data arrays. It has thus been possible to distinguish relatively unambiguously between quenching of the solvent and the solute when various heavy-atom quenchers were added to solutions of a series of substituted terphenyls. The method is found to be valuable in providing basic information about energy transfer steps in a multicomponent scintillator

[en] Heating organic liquid scintillator solutions has proven to be an efficient way to improve the time response in some cases. Higher temperatures increase the rates of diffusion-controlled energy transfer processes in dilute solutions and in solutions with relatively high viscosity at room temperature. Under these conditions both the excitation rate and the rate of intermolecular quenching, including concentration-quenching, become faster at higher temperatures. Except for specific concentration-quenching effects, little temperature dependence of the scintillator pulse parameters was observed in the more concentrated or in the less viscous systems

[en] Several liquid scintillator for formulations are described that were developed over the last several years on the Radiation-to-Light Converter program at EG and G Energy Measurements, Inc. The general aim of this program is to develop new scintillators that are needed for monitoring fast pulses of ionizing radiation. A large part of this effort has been directed toward new red scintillators for remote sensing applications, in which the scintillation pulses are to be transmitted to the detectors through long optical fibers. The main absorption band for red dyes is often at too long a wavelength for good overlap with the emission band of excited solvent molecules. In such cases, an intermediate wavelength shifter is used, whose absorption band overlaps well with the solvent emission, and whose emission overlaps the absorption band of the final emitter. With a good intermediate dye, energy transfer to the final emitter will be so fast that little energy is lost by radiation from excited singlets of the intermediate, and the overall time response is usually improved. Pseudo-cumene has been found to be the most efficient solvent for most nonpolar aromatic solutes, which usually emit a fairly short wavelengths, from near-ultraviolet to green light. Benzyl alcohol has been found to be an efficient solvent for most of the polar red-emitting laser dyes

[en] Two series of high-Z liquid scintillators have been developed and found to be useful for detection of X-rays and gamma rays in the energy range of about 4-200 keV. One type of solution is composed of pseudocumene (PC) as the solvent, 4,4''-di(5-tridecyl)-p-terphenyl as the scintillating solute, and tetramethyltin as the heavy-atom compound. A second type of solution contains a much faster but lower-yield solute, 4-bromo-4''-(5-hexadecyl)-p-terphenyl; the other components are the same. A tin loading of 22 weight percent in either of these solutions increses its sensitivity to 8 keV X-rays by a factor of 2.5 for a sample thickness of 1 mm. Well-resolved photopeaks were recorded for 122 keV gamma rays from ⁵⁷Co using solutions containing 28 and 49 weight percent tin. Several pulse parameters i.e., rise time, decay time, etc., of the radiation from solutions with and without added tin have been measured by exciting the solutions with pulsed electrons from a linac. The decrease in scintillation yield with increased tin loading was found to be proportional to dilution of the PC solvent. Moreover, decay times of the solutions were not affected by addition of tetramethyltin. Therefore, it is concluded that the heavy atoms do not actively quench the fluorescence from these solutions. (orig.)

[en] The modeling technique described in this paper was developed to aid in interpretation of the effects of various changes in scintillator formulations on the shape of scintillation pulses. For example, addition of quenchers to single-solute systems can quench either the solute or excited solvent, or both, and it is useful to understand these effects in tailoring a scintillator for optimum brightness or speed for a specific application. In multisolute scintillators, an understanding of the detailed energy transfer steps is also desirable. Inspection of pulse rise and decay times often give general information on these effects, but a more detailed interpretation is complicated by several factors. First of all, many scintillators are fast enough (1-2 ns FWHM) so that empirically determined pulse parameters, especially rise times, are significantly affected by the response time of the measuring system. In addition, decay times are difficult to determine until the signal has decayed considerably past the peak where noise can become a problem. It occurred to us that it might be possible to understand the effects of additives on the rise and decay constants that determine the true pulse shape if we synthesized theoretical pulse shapes, folded in the system response function, and overlaid the resulting curves on the raw data arrays. The results have been gratifying in that in most cases it has been possible to distinguish relatively unambiguously between quenching of the solvent and the solute when various heavy-atom quenchers were added to solutions of a series of substituted terphenyls

[en] In this experiment, an attempt was made to raise the average Z of a scintillation solution with as little attendant quenching as possible. Since high-Z atoms quench by means of a close encounter, as stated above, such encounters are minimized by the use of alkyl groups substituted on the solvent, solute, and heavy atoms. The aromatic compound 1,2,4-trimethylbenzene (pseudocumene) was used as the solvent; 4,4''-di(5-tridecyl)-p-terphenyl as the solute; and tetrabutyltin as the high-Z material. Various experiments were performed with less protected solvents and heavy atoms. These include benzene, toluene, p-terphenyl, bromobutane, and bromobenzene

[en] Organic scintillator solutions with decay times as fast as 500 ps and with relatively high conversion efficiencies have been developed. The intramolecular quenching was achieved through the novel approach of adding a bromine atom to the 3- or 4-position of para-oligophenylenes, the fluorescent solutes in these binary solutions. The bromine serves to enhance singlet-to-triplet intersystem crossing in the chromophore, causing a reduction in the scintillation yield and a concomitant reduction in the decay time. The very fast value given above probably also involves some intermolecular self-quenching at high concentration. In addition, the bromine reduces the symmetry of the molecules, thereby increasing their solubility. Finally, an alkyl chain on the opposite para position further increases the solubility and also increases the immunity of the chromophore to quenching. The decay times for binary liquid solutions in toluene (at the indicated concentrations) were 0.51 ns for 4-BHTP (0.14 M), 0.75 ns for 3-BHTP (0.14 M), 0.57 ns for 3-BTP (0.14 M), and 1.3 ns for 4-BHQP (0.06 M). Binary plastics with 4-BHTP as the solute in concentrations up to 0.14 M were cast in polystyrene. The shortest decay time, 0.40 ns, was measured for the 0.14 M concentration. A plastic scintillator containing 3-BTP (0.11 M in polystyrene) had a decay time of 0.85 ns. These results compare favorably with the plastic scintillator BC-422 whose decay time is about 1.4 ns. (orig./HSI)