Fission Products (by Element) - Lanthanides (lanthanum-139, Cerium-140 To 144, Neodymium-142 To 146, 148, 150, Promethium-147, and S

Lanthanides (lanthanum-139, Cerium-140 To 144, Neodymium-142 To 146, 148, 150, Promethium-147, and S

A great deal of the lighter lanthanides (lanthanum, cerium, neodymium, and samarium) are formed as fission products. It is interesting to note that in Africa at Oklo where the natural nuclear fission reactor operated millions of years ago the isotopic mixture of neodymium is not the same as 'normal' neodymium, it has an isotope pattern very similar to the neodymium formed by fission.

In the aftermath of criticality accidents the level of 140La is often used to determine the fission yield (in terms of the number of nuclei which underwent fission).

Samarium-149 is the second most important neutron poison in nuclear reactor physics. Samarium-151, produced at lower yields, is the third most abundant medium-lived fission product but emits only weak beta radiation. Both have high neutron absorption cross-sections, so that much of them produced in a reactor are later destroyed there by neutron absorption.