Mossbauer high-pressure experiments

Fig. 3.43 Elements with Mossbauer isotopes are untinted. The energies are transition energies (for high-pressure candidates). Isotopes that have been used in high-pressure experiments are framed by bold lines.

Almost every modem spectroscopic approach can be used to study matter at high pressures. Early experiments include NMR [ ], ESR [ ] vibrational infrared [33] and Raman [ ] electronic absorption, reflection and emission [23, 24 and 25, 70] x-ray absorption [Tf] and scattering [72], Mossbauer [73] and gems analysis of products recovered from high-pressure photochemical reactions [74]. The literature contains too many studies to do justice to these fields by describing particular examples in detail, and only some general mles, appropriate to many situations, are given. 

Recent developments in Mossbauer spectroscopy may also lead to interesting high-pressure applications. Many years ago it was proposed that the special properties of synchrotron radiation could be used to provide nuclear excitation without the use of radioactive sources, and recently progress with modern synchrotron-radiation sources could mean that such experiments could be feasible for Fe. Due to the natural high collimation of the most favourable undulator radiation from synchrotron insertion devices, one can expect that high-pressure measurements will be one of the first applications of this technique, which will eventually be applied to isotopes for which no suitable radioactive sources exist. " ... 

Caution For safety procedures see Appendix 2. Since special hardware, software, experience, and special permission are required to work with radioactive sources for high-pressure Mossbauer spectrometry, any one interested in this subject is strongly advised to contact one of the groups already working in this field before any experimental work is begun. 

Measurements of the Mossbauer effect (Shenoy et al. 1972), showing no J-mixing, and high-pressure X-ray experiments (Leger et al. 1986) complete the many investigations done on UP. 

The situation with respect to high-pressure Mossbauer experiments is discussed in section 5. General systematics within the most thoroughly studied series of intermetallics are presented in sectii n6. Section 7 briefly highlights the spin-glass behavior of a class of lanthanide and actinide intermetallics. 

To reach pressures above 15 GPa the B4C anvils have to be replaced by a stronger material. The diamond anvil cell has been proven most suitable during the last decade. Unfortunately, due to the high costs of the anvils the dimensions of the sample have to be kept small typically, the area of the sample is about a factor of 100 smaller as compared to B4C anvils. For X-ray and optical measurements this is not a problem. For Mossbauer experiments diamond anvil cells have been employed only with transitions which exhibit a large recoil-free fraction, in particular with Fe, and the lanthanide Eu. The spectrometer to be described is based on a design reported earlier (Bassett et al. 1967, Huber et al. 1977). Experiments can be carried out at cryogenic temperatures. 

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