subtraction

The passage around this formula

The rapid neutron-capture process runs the opposite calculation. Where the s-process waits for each nucleus to settle before moving on, the r-process floods a small volume of matter with so many free neutrons that a nucleus can capture several before it has any real chance to beta-decay: $\tau_{\beta^-} \gg \tau_n \qquad \text{(r-process)}$. Under these conditions the reaction path runs far from the valley of stability, out toward the neutron drip line, where nuclei are so neutron-rich that adding one more neutron barely binds at all [ 8 ] . Capture continues, isotope after isotope, until it reaches a nucleus at one of the neutron shell closures — the magic neutron numbers 50, 82 and 126 — where the next capture is…

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