Calibration of the isomer shift of the 14.4 keV excited state of 57Fe

A. MUDARRA NAVARRO; C. E. RODRÍGUEZ TORRES; L. A. ERRICO

Lima, Peru

Conferencia; XII Latin American Conference on Mossbauer Effect; 2010

Universidad de Lima, Peru

Trabajo presentado en forma de poster durante la conferencia Hyperfine interaction measurements are widely used experimental techniques that provide local information on the interaction of a probe nucleus with the surrounding electronic charge distribution. In particular, Mössbauer spectroscopy (MS) is a widely used method for investigations of solid state systems on an atomic scale. One of the parameters that can be determined by MS is the isomer shift, which provides information on the local chemical bond. This parameter depends on the solid state environment as well as on the structure of the nucleus. The isomer shift could be expressed as d =a(rA-rA), were rA and rS  stand for the electron charge densities at the nuclear positions (the contact densities) in two different solid state environments, here denoted the absorber (A) and the source (S) materials, respectively. The calibration constant a (the nuclear quantity) must be determined to allow a reliable conversion between the measured quantities and the microscopic parameters of the solid, i.e., the electron contact density.             The calibration of Mössbauer experiments has been an issue for a long time. a can be obtain, in principle, from nuclear models, but the accuracy of such models is not always good enough. More accurate is the determination of this parameter from comparison of calculated electron contact densities with corresponding experimental isomer shifts. This scheme was successful applied, for example, to the 23.88-keV transition in 119Sn [1] and the 37.15-keV transition in 121Sb [2]. More recently, a calibration of the isomer shift for the 14.4-keV transition in 57Fe was presented [3].             In this work, the Full-Potential Augmented Plane-Wave plus local orbitals method has been used to calibrate isomer shift for the 14.4-keV resonant transition in 57Fe. Different approximations for the exchange and correlation potentials were explored. Calculations have been performed for different iron compounds, including metallic and oxides systems. The isomer shift calibration constant of a =−0.25 a.u.3 mm s−1 has been obtained, in good agreement with the most recent result.   [1] A. Svane, N. E. Christensen, C. O. Rodriguez, and M. Methfessel, Phys. Rev. B 55, 12572 (1997). [2] A. Svane, Phys. Rev. B 68, 064422 (2003). [3] U. D. Wdowik and K. Ruebenbauer, Phys. Rev. B 76, 155118 (2007).