heavy ion

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The nucleus of a heavy element, such as gold. When such nuclei are caused to collide at high velocities, new elements are created.
• noun A charged microscopic particle that forms when an ion attaches to a dust mote or similar object.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun nuclear physics An ionized atom that is usually heavier than helium.