refers to an ionized
atom which is usually heavier than helium
. Heavy-ion physics is devoted to the study of extremely hot nuclear matter and the collective effects appearing in such systems, differing from particle physics
, which studies the interactions between elementary particles
. Together, these two subjects are denoted high-energy physics
In nuclear physics, the nuclei used as beam particles are generally completely ionized. 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, copper, tungsten, gold, lead, and uranium.