The rate of capture depends on the capture cross section and the stellar neutron density. If the capture cross section is known, the neutron density at the place in a star where nucleosynthesis occurred can be inferred from the abundance of 151 Eu and 152 Sm observed in nature. Thus, an accurate knowledge of the neutron capture cross section on certain radioactive isotopes can lead to an estimate of an important stellar parameter, the neutron density, and a deeper understanding of how stars work. S-process path near 151 Sm. Red indicates unstable nuclei, and blue indicates stable nuclei observed in nature.
Heavy outlines indicate nuclei that are produced only by the s-process.
Measurements on unstable nuclei are complicated by the need to handle radioactive targets safely. The Los Alamos National Laboratory offers several experimental facilities that combine to give it a capability that is unique in the world to make these measurements. First, there is the intense neutron source of the Manuel Lujan Jr. Neutron Scattering Center. Next, there is the ability to produce and handle radioactive targets by the Nuclear and Radiochemistry Group of the Chemical Science and Technology Division. In addition to radiochemistry expertise, this group has recently built the Radioactive Species Isotope Separator, a magnetic isotope separator specifically designed to separate highly radioactive isotopes.