of free neutrons. At some time following the neutron captures, the nucleus beta-decays back to the line of stability (just as with fission products) resulting in a stable isotope of the same mass number A, and normally the most neutron-rich of those.

Early studies theorized that 10²⁴ free neutrons per cm³ would be required, for temperatures of about 1 GK, in order to match the waiting points, at which no more neutrons can be captured,