Scintillation Studies of Organic Compounds in a Supercooled Molten State

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Abstract
When the crystals (obtained by crystallization from certain solvents) of a number of low‐molecular‐weight organic compounds (11 derivatives of 2‐phenylindole and two derivatives of p‐quaterphenyl) were melted and recooled to room temperature, rather stable nonrecrystallizing, supercooled melts were obtained. The consistency of these at room temperature varied from rather viscous oils to rigid glasslike masses. Their stability also varied over a wide range; from one day to at least several years. The response of these amorphous, pure scintillators to excitation by energetic electrons was measured relative to a standard liquid scintillator solution (gas‐free, 3‐g/liter PPO—toluene solution) which was assigned a value of 100. The very stable (at least several years) and rather rigid melt of 12,23,32,43‐tetramethyl‐p‐quaterphenyl exhibited a relative response of 92. The supercooled melt of N‐isoamyl‐3,2′‐ethyleno‐2‐phenylindole showed a relative response of 125 and remained amorphous with a consistency at room temperature of a thick grease for greater than nine months if maintained under evacuated conditions. The fluorescence spectra of these compounds in the undiluted, supercooled state and in a toluene solution (mole fraction of about 0.001) were measured for excitation by 315‐mμ radiation. In some cases there were differences in the measured spectra depending on the type of sample.