Swift heavy ions are the components of a type of

particle beam A particle beam is a stream of charged or neutral particles. In particle accelerators, these particles can move with a velocity close to the speed of light. There is a difference between the creation and control of charged particle beams and ne ...

with high enough energy that electronic stopping dominates over nuclear stopping.M. Toulemonde, W. Assmann, C. Dufour, A. Meftah, F. Studer, and C. Trautmann, Experimental phenomena and thermal spike model description of ion tracks in amorphisable inorganic insulators, Mat. Fys. Medd. Kong. Dan. Vid. Selsk. 52, 263 (2006). They are accelerated in

particle accelerator A particle accelerator is a machine that uses electromagnetic fields to propel charged particles to very high speeds and energies, and to contain them in well-defined beams. Large accelerators are used for fundamental research in particle ...

s to very high energies, typically in the

MeV In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacu ...

GeV GEV may refer to: * ''G.E.V.'' (board game), a tabletop game by Steve Jackson Games * Ashe County Airport, in North Carolina, United States * Gällivare Lapland Airport, in Sweden * Generalized extreme value distribution * Gev Sella, Israeli-Sou ...

range and have sufficient energy and mass to penetrate solids on a straight line. In many solids swift heavy ions release sufficient energy to induce permanently modified cylindrical zones, so-called

ion track Ion tracks are damage-trails created by swift heavy ions penetrating through solids, which may be sufficiently-contiguous for chemical etching in a variety of crystalline, glassy, and/or polymeric solids. They are associated with cylindrical d ...

s. If the irradiation is carried out in an initially crystalline material,

s consist of an amorphous cylinder. Ion tracks can be produced in many amorphizing materials, but not in pure metals, where the high electronic heat conductivity dissipates away the electronic heating before the

has time to form.

Definition

Heavy ion beams are generally described in terms of their energy in Mega electron volts (MeV) divided by the mass of the atomic nucleus, written "MeV/u". In order for an ion beam to be considered "swift", the constituent ions should be

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon mak ...

or heavier, and the energy such that the beam particles have a velocity comparable to the Bohr velocity.

Ion track formation

The mechanisms by which ion tracks are produced are subject to some debate. They can be considered to produce thermal spikes in the sense that they lead to strong lattice heating and a transient disordered atom zone. However, at least the initial stage of the damage might be better understood in terms of a

Coulomb explosion In condensed-matter physics, Coulombic explosions are a mechanism for transforming energy in intense electromagnetic fields into atomic motion and are thus useful for controlled destruction of relatively robust molecules. The explosions are a pr ...

mechanism. Regardless of what the heating mechanism is, it is well established that swift heavy ions typically produce a long cylindrical track of damage in insulators, which has been shown to be underdense in the middle, at least in SiO₂.

Applications

Swift heavy ion tracks have several established and potential practical applications. Ion tracks in polymers can be etched to form a nanometer-thin channel through a polymer foil, so called track etch membranes. These are in industrial use. Irradiation of polyimide resists have potential to be used as templates for

nanowire A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre (10−9 metres). More generally, nanowires can be defined as structures that have a thickness or diameter constrained to tens of nanometers or less ...

growth. Tracks can also be used to sputter materials. They can also be used to elongate nanocrystals embedded in materials. SHI irradiation can also be used for structural modification of nanomaterials.Mendoza, C., S. Peuget, T. Charpentier, M. Moskura, R. Caraballo, O. Bouty, A. H. Mir, I. Monnet, C. Grygiel, and C. Jegou. "Oxide glass structure evolution under swift heavy ion irradiation." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 325 (2014): 54-65. https://doi.org/10.1016/j.nimb.2014.02.002

References

{{Reflist Condensed matter physics Radiation effects