Multicomponent activation detectors combine in single composite detectors about 10 resonance or 10 threshold reactions. The detectors are so designed and optimized that all induced activities can be simultaneously measured using high resolution Ge(Li) gamma spectroscopy and interpreted to determine the energy spectra of inducing particles. This novel concept is described and exemplified by considering reactor neutron spectroscopy. Statistical tests are used to check that identical detectors can be fabricated.