s-process

Slow neutron capture by nuclei in massive stars. In the s-process, one starts with existing iron-group nuclei. Therefore, it would only be expected to take place in second-generation stars that collapsed out of the residue of a previous supernovaStellar explosion that expels much or all of the stellar material with great force, driving a blast wave into the surrounding space, and leaving a supernova remnant. Supernovae are classified based on the presence or absence of features in their optical spectra taken near maximum light. They were first categorized explosion. The flux of neutrons is small enough that rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-decay. These neutrons come from various reactions in the He-burning region of a red giantGiant and highly luminous red star in the later stages of stellar evolution after it has left the main sequence. These red stars have a relatively cool surface whose core has burned most of its hydrogen. Red giants lose parts of their atmospheres and thus provide new elements into interstellar starSelf-luminous object held together by its own self-gravity. Often refers to those objects which generate energy from nuclear reactions occurring at their cores, but may also be applied to stellar remnants such as neutron stars.. Hundreds to thousands of years may pass between successive neutron captures. In this situation, a seed nucleusCore of an atom, where nearly the entire mass and all positive charge is concentrated. It consists of protons and neutrons. will slowly capture neutrons, for example ⁵⁶Fe → ⁵⁷Fe → ⁵⁸Fe → ⁵⁹Fe, followed by ⁵⁹Fe → ⁵⁹Co (β decay). This process builds nuclei by climbing the line of stability, until ²⁰⁸Pb and ²⁰⁹Bi are reached. Beyond this point, no nuclei are stable enough to allow neutron capture to operate so that actinidesElements ⁸⁹Ac (actinium) to ¹⁰³Lr (lawrencium) found in the bottom row of the inner-transition elements of the periodic table. These elements are all radio active and the heavier in the series are unstable. For these elements the 5f orbital is the filling orbital. cannot be synthesized by the s-process.

The s-process is one of three nucleosynthesis processes that also includes the r-processRapid (hence "r") absorption of neutrons by atoms when the neutron flux is very high (~1022 neutrons per cm2/s) and the temperature is very high (T > 109 K). These conditions are hypothesized to occur during a supernova explosion/collapse or neutron star mergers. The time between neutron captures is much and the rp-processRapid proton capture (hence "rp") is a process that synthesizes elements by successive proton absorption and β+ decay; thus, it tracks somewhere between the valley of stability. The rp-process is one of three nucleosynthesis processes that also includes the s-process and the r-process..