• Tags: BE-per-nucleon, stability, curve
• Difficulty: Moderate

The BE/A curve is the most important graph in nuclear physics. Key features: (1) Very light nuclei (H-2: 1.1 MeV/nucleon) have low BE/A. (2) There's a sharp rise to He-4 $\frac{7.07 MeV}{nucleon}$, an anomalously high value due to the doubly-magic structure. (3) The curve peaks near Fe-56 $\frac{8.79 MeV}{nucleon}$ — the most tightly bound nucleus. (4) For A > 56, BE/A gradually decreases to about 7.6 MeV/nucleon for U-238. (5) Local peaks at He-4, C-12, O-16 indicate extra stability at magic numbers (2, 8, 20, 28, 50, 82, 126). The curve explains nuclear energy: fusion of light nuclei (moving right on the curve) and fission of heavy nuclei (moving left) both increase BE/A, releasing the difference as kinetic energy. The maximum energy release per nucleon comes from fusion (~6.7 MeV/nucleon for hydrogen to helium) versus fission (~0.9 MeV/nucleon for uranium).