Particle size distribution of np-Fe⁰ in different types of olivine and under different irradiation energy levels. The particle size labeled in each subfigure was the median particle size. Images (a)–(e) are Fa₂₉, (f)–(j) are Fa₅₀, (k)–(o) are Fa₇₁, and (p)–(u) are Fa₁₀₀. The numbers of np-Fe⁰ particles are negatively correlated with and the np-Fe⁰ particle sizes are positively correlated with increasing Fe content and irradiation energy.