Relativity and general physics

Although a number of possible applications of the Mossbauer effect have been suggested in the previous chapters, it is worthwhile to consider its use in general terms before developing the theme of more specific chemical application. Generally speaking, three broad areas can be defined in addition to that of the basic phenomenon of resonant absorption itself namely relativity and general physics, nuclear physics, and solid-state physics and chemistry. 

The advent of a radiation defined to 1 part in 10 to 10 prompted many physicists to find means of using it to verify some of the predictions of relativistic mechanics experimentally. In fact, many of the early Mossbauer experiments were directed towards such ends. After an early flood of papers, it was realised that many of the experiments could not provide an unambiguous proof of the validity of the physical laws with which they were predicted and interpreted, and consequently interest waned again. However, many of the experiments are extremely interesting in their own right, and some of them will now be outlined. 

The first published attempt to measure the shift was not conclusive [1], but in 1960 Pound and Rebka [2], using the Fe (14-4-keV) resonance in iron foils at a height separation of 22-5 m, showed that the experimental shift was 

0-94 010 of that predicted. Later experiments have given values of 

0-859 0-085 [3] and probably the most accurate value, 0-9970 i 0-0076 [4, 5]. In this work scrupulous attention must be paid to the elimination of small temperature differentials between source and absorber because of the possibility of spurious results due to the second-order Doppler shift (see p. 50). Although Mossbauer lines with a definition better than that of Fe are known, the technical difficulties involved have prevented their use in gravitational red shift experiments. 

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