This work details an application of collinear resonance ionization spectroscopy for the separation of short-lived isomeric states and their subsequent study with decay spectroscopy. It reports the successful construction of a novel decay spectroscopy apparatus that can operate at pressures below 1 x 10^-9 mbar. The method is demonstrated by separating the nuclear ground and isomeric states of 204Fr and performing alpha-decay spectroscopy. An equivalent mass spectrometer would require 4.6 million times as much resolution to achieve the same result. This work unambiguously confirms the existence of a second isomeric state in 204Fr. The author also demonstrates the effectiveness of this method for laser spectroscopy and identification of hyperfine-structure components with energy tagging. This method was successfully used in 202Fr to identify ground and isomeric states. The measurement of 202Fr reported in this thesis demonstrates a factor of 100 improvement in sensitivity compared to state-of-the-art fluorescence techniques. The work reported in this thesis won the author the IOP Nuclear Physics Group Early Career Prize.weiterlesen