Abstract: A method for separation, identification, and quantification of radioactive species in an environmental fluid, such as surface or ground water, by passing the fluid through a sheet article. The sheet article is an essentially homogenous, fibrous or fibrillated, matrix or membrane that includes (1) ion-specific separators that sorb or react with the targeted radioactive species and (2) scintillators which emit light in response to radioactive emissions from the targeted species. The separators can be macrocyclic ligand-containing particles. The scintillators can be particles, fibers, a coating on the particles, or a coating on the fibrous matrix or membrane. The scintillator can be an organic scintillator or an inorganic crystalline scintillator. In one embodiment both the scintillator and the separator are incorporated into the same particle or fiber. A scintillation counter can be used to detect and quantify the emitted light.