The critical micelle concentration and the phase boundary between isolated surfactant molecules and aggregates are probed via fluorescence spectroscopy and a Compton spectrum quenching technique for aqueous and toluenic solutions of Triton X-100 (TX-100). The internal fluorophore of TX-100 provides a convenient probe for the fluorescence measurements, and the appearance of redder bands in the fluorescence spectra and their relationship with aggregation (clustering of TX-100) phenomena is addressed. The Compton spectrum quenching approach makes use of quench indicating parameters (QIPs) commonly measured in liquid scintillation counting experiments. Phase boundaries identified by the QIP-based approach are in excellent accord with the fluorescence-based approach.