157Gd

157Gd is a stable isotope of the element gadolinium (atomic number 64) with a mass number of 157. It is one of the seven stable isotopes that occur naturally in gadolinium and accounts for about 15.7% of natural gadolinium. As a stable isotope, 157Gd does not undergo radioactive decay under ordinary conditions.

From a nuclear physics perspective, 157Gd stands out for its very high thermal neutron capture cross section among stable isotopes. The cross section is approximately 2.5 × 10^5 barns, making it an exceptionally efficient absorber of thermal neutrons. This property has practical implications in nuclear technology, where gadolinium compounds are used as burnable absorbers and, in some reactor designs, as part of control materials to help manage reactivity and shielding.

Occurrence and composition: 157Gd occurs naturally in minerals containing gadolinium, such as gadolinite, and is distributed alongside the element’s other stable isotopes in the Earth's crust. The precise isotopic composition can vary between natural samples, but the isotope is a stable and significant component of natural gadolinium.

Applications and context: The strong neutron absorption of 157Gd contributes to the role of gadolinium in nuclear reactors, where it helps regulate neutron flux and reactor power over the fuel cycle. In addition to industrial uses, gadolinium isotopes are of interest in scientific studies of isotopic chemistry and nuclear processes.