Abstract: An optical radiation measurement apparatus is provided. The apparatus has at least one radiation detector for measuring electromagnetic radiation emitted from at least two radiation sources. Separate radiation channels are provided in a channel member in order to provide a radiation path between the radiation sources and the radiation detector, which is common to all of the radiation sources.

Abstract: A method of regenerating etchant and recovering etched metals. Etching solution, which is overladen with metal cations is passed through a cation exchange unit. Subsequently, the etching solution, which is diminished in metal cation concentration, is returned to the etcher sump. The cation exchange unit is then rinsed with deionized water to remove residual etching solution, with the effluent being conveyed to a metal recovery unit. The cation exchange unit is then rinsed with an aqueous solution of an acid to remove cations and to regenerate the cation exchange unit. The effluent from this rinsing is also conveyed to the metal recovery unit. The cation exchange unit is then rinsed with deionized water to remove residual acid, with this effluent likewise being conveyed to the metal recovery unit. Subsequently, a selectolyte solution is passed through the cation exchange unit to enhance the cation retention property thereof. The effluent is conveyed to a storage container.