Recoilless Nuclear Resonance Absorption

Abstract

The resonant scattering of gamma rays constitutes the nuclear analogue to the well-known optical fluorescence effect. Although its existence was already predicted in 1929 (1) it was actually observed only in 1951 (2). Since then several methods have been developed which led to the observation of resonance scattering or absorption in a number of first excited nuclear states. A major breakthrough took place in 1958 when the phenomenon of recoilless nuclear resonance absorption was discovered (3). This new absorption effect provided a means for the elimination of the energy losses by recoil, these being the most serious obstacle for the observation of nuclear resonance absorption or scattering. Simultaneously gamma lines of utmost narrowness became available. It is this particular feature which opened a wide range of applications for the new effect, in such fields as nuclear physics, solid state physics, and relativity, and made possible investigations which could not even be considered only a few years ago. This article is an account of the major features of the recoilless nuclear resonance absorption: the treatment emphasizes the general aspects, and the selection of references was restricted accordingly. For a complete list of references the reader is referred to the compilation of Frauenfelder (4) and to the proceedings of two conferences (5, 6) which were solely devoted to the subject under discussion.