Quantitative characterization of complex microdefect structures in annealed silicon crystals (1150 <$E symbol Р>C, 40 h) and their transformations after exposing for one day in a weak magnetic field (1 T) has been performed by analyzing the rocking curves, which have been measured by a high-resolution double-crystal X-ray diffractometer. Based on the characterization results, which have been obtained by using the formulas of the dynamical theory of X-ray diffraction by imperfect crystals with randomly distributed microdefects of several types, the concentrations and average sizes of oxygen precipitates and dislocation loops after imposing the magnetic field and their dependences on time after its removing have been determined.