Gadolinium

About Gadolinium

Gadolinium is the lanthanide chemists reach for when they need unpaired electrons in bulk. Its half-filled 4f⁷ shell gives Gd³⁺ seven unpaired f-electrons — the maximum Hund's-rule alignment any ion in the periodic table can muster — which translates to a huge magnetic moment with no orbital contribution. That property does the work in two completely different fields. In MRI, Gd³⁺ chelated to DTPA, DOTA, or related polyaminocarboxylate ligands shortens the T₁ relaxation time of nearby water protons, brightening the tissues where the contrast agent accumulates. Tens of millions of these scans are run each year. In nuclear engineering, the natural-abundance isotope Gd-157 has the largest thermal neutron capture cross-section of any nuclide (about 254,000 barns), which makes gadolinium the active ingredient in burnable poison rods that flatten reactivity over a fuel cycle. Gadolinium metal is also the textbook example of the magnetocaloric effect — it heats up by a few kelvin when magnetized at room temperature — and is the active material in the prototype magnetic refrigerators being developed as a CFC-free cooling alternative.