Measurement of Grain Size of Iron Hydroxide with M ssbauer Effect Shibata lab. Yutaka Fujiwara May 27th, 2005 When iron rusts in outdoor atmosphere, grains of iron hydroxide are formed on the surface. (Graduation study at Gakushuin University) Motivation; The size of grain is related with mechanism of the rusting. We can measure grain size of iron hydroxide with M ssbauer effect. I have done solid state physics using nuclei gamma-ray. Recoilless absorption of -ray by Fe nuclei. What is M ssbauer effect? Fe nuclei in grain are recoilless because the atomic bonding is strong. Hyperfine energy level of 57 Fe Proportional counter 57 Fe 57 Co -ray ( 14.4keV) Transmitted -ray Doppler shift Relative transmission (%) Velocity (mm/s) Energy shift (10 -8 eV) M ssbauer spectrum of Fe The sample is grain of -FeOOH. How well can we determine the size of grain of -FeOOH with M ssbauer spectrum? 66 O/OH Fe Grain of -FeOOH Crystal structure of -FeOOH -FeOOH is iron hydroxide which is anti-ferromagnetic material. T=300K Where K u =1000J/m 3 (ns)V(m 3 ) 41.84 Direction of easy magnetization axis Direction of Sublattice magnetization Drastic Change of M ssbauer Spectrum. Superfine grain reverses its direction of hyper-fine field with relaxation time . Simulation Relaxation time Direction of easy magnetization axis Direction of Sublattice magnetization Superfine grain (nano order) Reversing Hyper-fine field C = 0.1ns Relaxation time Dependence of on V at various temperature (K u =1000J/m 3 ) Superfine grain reverses its direction of hyper-fine field every relaxation time . How to Analysis