[en] Threshold reactions induced by reactor fast neutrons are well recognized. The concentration of Fe and Ni were determined in nine geological samples by activation analysis with reactor fast neutrons using the threshold reactions 5^4Fe( n,p)⁵⁴Mn and ⁵⁸Ni ( n, p )'5⁸Co respectively. The fast neutron flux was determined using the reactions ⁹²Mo(n, 2n)⁹²mNb and ⁹⁵Mo(n,p)⁹⁵Nb. The determined concentration of Fe and Ni in the samples were checked by determining them in the GSJ JB-1 reference material using the same , ( p, n) reactions. There are a good agreement between the measured and recommended values. The concentrations of Fe were also determined by the ) , ( n, γ) capture reactions in the geological samples and the JB-1 reference material using the K_θ- NAA method. There are good agreements between the determined concentrations from the ) , ( p, n) and the ( γ, n) reactions.