Mössbauereffektmessungen am 79,5 keV-Niveau von Gd158

Mössbauer effect measurements with the 79,5 keVγ-transition in Gd¹⁵⁸, populated by thermal neutron capture in Gd¹⁵⁷ are reported. In Gd metal, GdF₃ and GdCl₃, the values obtained for the electric field gradient are (?0.7±0.4), (11.9±5.0) and (?7.5±0.5) · 10¹⁷ V/cm² respectively. The internal magnetic field in Gd metal was measured to beH _int=312±23 kG and we derived for theg factor of the 2 + level the valueg _R=0.385±0.022. The change of the mean square nuclear radius between the ground state and the first excited stateΔ 〈r²〉=+(0.4±0.3) · 10^?3 fm², as extracted from the measurements, will be compared with model calculations of nuclear rotation.