Symbol a_P

The passage around this formula

where $\alpha$ , $\beta$ , and $\gamma$ collect the volume, surface, Coulomb, and asymmetry contributions and the pairing term $\delta(A)$ shifts the curve up or down depending on whether N and Z are both even or both odd. For odd A , exactly one of N , Z is even and the pairing term vanishes, giving a single parabola with one minimum: one value of Z at that mass number is the most tightly bound, and every other isobar decays toward it by beta-minus emission (if it sits to the neutron-rich side) or by positron emission or electron capture (if it sits to the proton-rich side). For even A , the pairing term splits the curve into two parabolas — one for even-even nuclei sitting lower in mass (more…

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