'Heavy ion' refers to an
ionized atom which is usually heavier than
carbon. The term is
applied in reference to beams of particles used to produce
heavy ion collisions in
high energy nuclear physics (an area of research that is sometimes
mistakenly included within
particle physics or
high energy physics).
In nuclear physics, the atoms used as beam particles are generally completely
ionized, so that they are bare atomic nuclei. The nuclei can be directed to a fixed target, or can be split into two beams moving in opposite directions that
are brought into collision at a well-defined spot.
Heavy ion nuclei most often used in nuclear physics experiments include
carbon,
silicon,
tungsten,
gold,
lead,
and
uranium.