New Fluors for Radiation Tolerant Scintillators
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Abstract The new generation of high energy accelerators - LHC, CEBAF, RHIC - have encouraged the development of more robust plastic scintillators. Monitors and detectors for these machines will require plastic scintillator with greater radiation tolerance. Although the major cause of radiation damage in plastic scintillator is the creation of color centers in the base plastic, the most successful approach to date has been to utilize fluors which circumvent, rather than solve, the radiation damage problem. Two techniques have been found to be useful. First, increase the concentration of fluors so that the optical density of the fluors for absorption of the scintillation photons remains much higher than the optical density of the radiation induced color centers. Second, use fluors which emit at longer wavelengths than traditional fluors, thus avoiding radiation induced color centers. The present work attempts to meet these requirements by modifying the structure of the 3-HF molecule.
Introduction
Scintillating plastics have been in use as particle and x-ray detectors in nuclear and particle
physics for many years. Plastic scintillators can be cheaply produced in sheet, rod or fiber forms and are easily machined to a desired shape. They can be made to be fast (a few nano-seconds) and emit at a favorable wavelength.I.2 Furthermore, they are much more radiation resistant than some other common radiation detectors such as lead glass or sodium iodide. Nonetheless, the demands of the newest generation of accelerator-based experiments substantially exceed the capabilities of available plastic scintillators in regard to radiation tolerance. 3 In the past few years, several groups have searched for more radiation tolerant plastic scintillators. Although there has been some success in finding substitutes for polystyrene in limited roles, a complete, rad-hard substitute for polystyrene has not been found. For example, there is nothing available which can substitute for polystyrene in scintillating fibers. Substitutes are either more radiation susceptible, or do not have acceptable attenuation lengths or light yield. The slow progress in finding better plastic base materials has prompted efforts to circumvent the radiation damage problem by finding better fluors. There are two additional criteria, which will be motivated in the next section, which make a fluor of interest for use in radiation tolerant scintillators. The first criterion is that increasing the optical density of the secondary fluor makes the scintillator more robust towards irradiation. The secondary fluor must therefore be soluble enough to be used in high concentrations, or have a large extinction coefficient, preferably both. The second is that the longer (redder) the emission wavelength of a fluor, especially the final fluor, the more radiation tolerant a scintillator will be (other things being equal). 173 Mat. Res. Soc. Symp. Proc. Vol. 348. 01994 Materials Research Society
The next section will present our rationale for the two additional criteria. The
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