 Fission-fragment mass distribution

The yield of fragments as a function of fragment mass number or mass fraction. Low-excitation actinide nuclear fission commonly gives two peaks, corresponding to complementary lighter and heavier fragments. Smooth liquid-drop fission energy by itself does not predict this yield: nuclear-shell structure and the dynamics of the descent toward scission matter. Increasing excitation can weaken shell effects and change the distribution. A two-peaked illustrative curve is therefore not a universal measured spectrum.