Method of Measuring the Mössbauer Effect

Abstract

THE Mössbauer effect¹ is of great value because of the extremely high energy resolution it provides, but it is often very difficult to measure, because it may be very small (for example, about 0.07 × 10⁻² per cent for zinc-67 in zinc metal²). Common values are about 1 per cent of the total absorption, and even these may be attained only at very low temperatures. A differential absorption of this order is very difficult to measure with precision, particularly at low temperatures, because the stability of the equipment must be exceptionally high. For these reasons, most of the detailed applications have involved the use of the 14.4-keV. line of iron-57, which gives about 14 per cent differential absorption at room temperature. The parent nuclide is cobalt-57, which is difficult to prepare; moreover, the internal magnetic fields in iron cause a hyperfine splitting, and the low energy (14.4 keV.) makes the radiation difficult to use. Further, very strong sources are needed, because the distance from source to counter is large and because the source is used for only a small proportion of the total time. Finally, the velocity of the source relative to the absorber varies (owing to the curvature of the path) and is known only to 10 per cent or so if a system similar to Mössbauer's original one is used.