The nuclear magnetic moment of 190Ir and the directional distribution of gamma rays in 190Os

Angular distribution of gamma transitions between levels in 190Os fed in the decay of 190Ir aligned in a rhenium single crystal have been measured at temperatures down to 2 mK. Multipole mixing ratios in both gamma and electron-capture transitions are deduced and compared with various nuclear models. The angular distribution coefficients are applied to interpret very small anisotropies observed when 190Ir is polarised in an iron host matrix, cooled to 2.5 mK. The deduced magnetic dipole moment of the 4+ ground state of 190Ir is |μ(190Ir;GS)|=0.04(1)μsub(N). Possible single-particle descriptions compatible with this result are suggested. (author)