 Mössbauer discovery experiment

Rudolf Ludwig Mössbauer found the effect during his Heidelberg work in 1957.^[ref] His 1961 lecture Recoilless nuclear resonance absorption of gamma radiation describes crystalline preparations using the $129\mathrm{keV}$ transition of the iridium isotope ${}^{191}\mathrm{Ir}$. Separate cryostats, lead collimation and a particle scintillation detector measured transmission. Liquid-air cooling of both preparations enhanced absorption; cooling only the source against a room-temperature absorber slightly reduced it. A rotating source cryostat supplied nearly constant projected velocities over selected arcs. Centimetres per second suppressed absorption relative to zero velocity; a nonresonant absorber supplied the comparison. This tested a narrow common emission/absorption energy beyond the detector's resolution. Temperature data alone had not established its width. The lecture cites the initial and direct-verification publications from 1958.^[ref]