ELEVENTH IN THE LANTHANOID SERIES

Holmium is often cited as having the highest magnetic strength (also known as magnetic moment) of any naturally occurring element. (See “Iron, Fe” on page 74 for more about magnetic moments.) But the comparable magnetic strength of its immediate neighbor dysprosium is acknowledged by the asterisk (*) after the word all.

When holmium is placed within a magnetic field, it draws the magnetic lines of force closer together. This concentrates the magnetic flux (which is a measure of the number of magnetic lines of force passing through a given surface), thus intensifying the magnetic field. A magnet’s strength can be improved by incorporating a piece of holmium into its poles. These pole pieces intensify the magnetic fields within the MRI machines used in hospitals.

Despite having some 35 known radioactive isotopes, all naturally occurring holmium exists exclusively as a single, non-radioactive isotope, holmium-165.

Holmium helps control the temperature within nuclear reactor cores by behaving as a burnable poison. The holmium preferentially burns up as it absorbs neutrons, preventing the nuclear chain reaction from overheating and running out of control.

Holmium-doped YAG solid-state lasers are routinely used in laser surgery due to their versatility and relative safety. (For more about YAG, see “Yttrium, Y” on page 114.)