A comparative study of troilite in bulk ordinary chondrites Farmington L5, Tsarev L5 and Chelyabinsk LL5 using M?ssbauer spectroscopy with a high velocity resolution

摘要

A comparative study of troilite in bulk ordinary chondrites Farmington L5, Tsarev L5 and Chelyabinsk LL5 was carried out using M?ssbauer spectroscopy with a high velocity resolution and two different fitting programs: in the first case the quadrupole interaction was treated as a perturbation to the first order on the nuclear Zeeman levels, whereas in the other case the full static Hamiltonian of the hyperfine interaction (magnetic + quadrupole) was taken into account for the excited and ground nuclear states. The first fit of the M?ssbauer spectra revealed a difference between the hyperfine magnetic field values as found for troilite in Farmington L5 (307.7 ± 0.2 kOe) and in both Tsarev L5 (311.3 ± 0.3 kOe) and Chelyabinsk LL5 (311.9 ± 0.5 kOe), although the spectral component of troilite could not be fitted satisfactorily. In contrast, the second fit resulted in a more accurate description of the troilite spectral component, and revealed a difference in the electric field gradient values found for troilite in Farmington L5 (-4.85 ± 0.03 - 10~(21) V/m~2) and in both Tsarev L5 (-4.68 ± 0.05 - 10~(21) V/m~2) and Chelyabinsk LL5 (-4.66 ± 0.04 - 10~(21) V/m~2), while the difference between the hyperfine magnetic field values was less pronounced.