Swift heavy ions are the components of a type of
particle beam
A particle beam is a stream of charged particle, charged or neutral particles other than photons. In Particle accelerator, particle accelerators, these particles can move with a velocity close to the speed of light. There is a difference between ...
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 electric charge, charged particles to very high speeds and energies to contain them in well-defined particle beam, beams. Small accelerators are used for fundamental ...
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 through an electric potential difference of one volt in vacuum. When us ...
or
GeV
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 through an electric potential difference of one volt in vacuum. When us ...
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 tracks. If the irradiation is carried out in an initially crystalline material,
ion tracks consist of an amorphous cylinder.
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
ion track 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; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...
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 mechanism.
Regardless of what the heating mechanism is, it is well established that swift heavy ions typically produce a long nearly cylindrical track of damage in insulators,
which has been shown to be underdense in the middle, at least in SiO
2.
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
Polyimide (sometimes abbreviated PI) is a monomer containing imide groups belonging to the class of high-performance plastics. With their high heat-resistance, polyimides enjoy diverse applications in roles demanding rugged organic materials, suc ...
resists have potential to be used as templates for
nanowire
file:[email protected], upright=1.2, Crystalline 2×2-atom tin selenide nanowire grown inside a single-wall carbon nanotube (tube diameter ≈1 nm).
A nanowire is a nanostructure in the form of a wire with the diameter of the order of a nanometre ( ...
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
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Condensed matter physics
Radiation effects