155Gd

155Gd, or gadolinium-155, is a stable isotope of the element gadolinium (Gd) with mass number 155. It is one of the naturally occurring isotopes of gadolinium and accounts for approximately 14.8% of natural gadolinium.

It has 64 protons and 91 neutrons. As a stable, odd-A nuclide, it does not undergo radioactive decay under normal conditions.

A notable feature of 155Gd is its very large thermal neutron capture cross section. The isotope, together with 157Gd, dominates the absorption of thermal neutrons in natural gadolinium. This property makes gadolinium a strong neutron absorber in applications that require neutron shielding or control of reactivity.

Occurrence and applications: 155Gd occurs naturally in gadolinium at about 14.8% abundance. Because of its high neutron absorption, gadolinium-containing materials are used in neutron shielding and, in some reactor designs, as a burnable poison or in fuel assemblies to help control reactivity. The isotope also features in measurements of neutron capture cross sections and in detector calibration where precise neutron absorption data are needed.

See also: 157Gd.