## Gamma-ray Source

Fe Mössbauer spectroscopy uses a Co source. The decay scheme of this isotope is shown in Figure 4.1. The half-life of Co is and decays by electron capture to the excited state of Fe. This excited state decays to the excited state ( ) or to the ground state by gamma-ray emission. The state decays in turn to the ground state by gamma-ray emmission or internal conversion. The ratio of these two decay rates are given by Equation 2.28, where for Fe. The half-life of the excited state is , giving a Mössbauer gamma-ray with a linewidth of . The linewidth of a resonant emission and absorption event is thus in perfect conditions.[7]

The sources used in this thesis are fabricated by diffusing Co atoms in a rhodium foil matrix: the rhodium matrix provides a solid environment for the Co atoms with a high recoil-free fraction and a cubic, non-magnetic site environment to produce mono-energetic gamma-rays. The initial source activities are with a linewidth of measured with a thin absorber.

Dr John Bland, 15/03/2003