Segera setelah keruntuhan inti pada supernova, terdapat [[fluks neutron]] sangat tinggi (pada orde 10<font size= "-1"><sup>22</sup></font> neutron per cm<font size= "-1">²</font> per detik) dan [[suhu]], sehingga [[penangkapan neutron]] terjadi lebih cepat daripada [[peluruhan beta]] jauh dari kestabilan, artinya bahwa '''proses r''' "berlari" di sepanjang [[garis drip neutron]].
<!--
Immediately after a core-collapse supernova, there is an extremely high [[neutron flux]] (on the order of 10<font size= "-1"><sup>22</sup></font> neutrons per cm<font size= "-1">²</font> per second) and [[temperature]], so that [[neutron capture]]s occur much faster than [[beta decay|beta-minus decays]] far from stability, meaning that the '''r-process''' "runs up" along the [[neutron drip line]]. The only hold-ups inhibiting this process of climbing the neutron drip line are a notable decrease in the neutron-capture [[Nuclear cross section|cross section]] at nuclei with closed neutron shells, the competing photodisintegration [(<math>\gamma</math>,n)] reaction rates, and the degree of nuclear stability in the heavy-isotope region, which terminates the r-process when such nuclei become readily unstable to spontaneous fission (currently believed to be in the neutron-rich region near ''A'' = 270 (number of nucleons) in the [[table of nuclides|chart of nuclides]]). After the neutron flux decreases, these highly unstable [[radioactive decay|radioactive]] nuclei quickly decay to form stable, neutron-rich nuclei. So, while the [[s-process]] creates an abundance of stable nuclei with closed neutron shells, the r-process creates an abundance of nuclei about 10 [[atomic mass unit]]s below the s-process peaks, as the r-process nuclei decay back towards stability on a constant ''A'' line in the chart of nuclides.
