Electron
irradiationIrradiation is the process by which an item is exposed to radiation. The exposure can be intentional, sometimes to serve a specific purpose, or it can be accidental...
is a process which involves using electrons, usually of high energy, to treat an object for a variety of purposes. This may take place under elevated temperatures and nitrogen atmosphere. Possible uses for electron irradiation include
Sterilization (microbiology)Sterilization refers to any process that effectively kills or eliminates transmissible agents from a surface, equipment, article of food or medication, or biological culture medium. Sterilization does not, however, remove prions...
and to
cross-linkCross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...
polymers.
Electron energies typically varies from the keV to MeV range, depending on the depth of penetration required. The irradiation dose is usually measured in
Gray (unit)The gray is the SI unit of absorbed radiation dose due to ionizing radiation .-Definition:One gray is the absorption of one joule of energy, in the form of ionizing radiation, by one kilogram of matter....
but also in
MradsThe rad is a unit of absorbed radiation dose, with symbol rad. The rad was first proposed in 1918 as "that quantity of X rays which when absorbed will cause the destruction of the [malignant mammalian] cells in question..." It was defined in CGS units in 1953 as the dose causing 100 ergs of energy...
. Where 1Gy is equivalent to 100rad.
In polymers, an
electron beamCathode rays are streams of electrons observed in vacuum tubes, i.e. evacuated glass tubes that are equipped with at least two metal electrodes to which a voltage is applied, a cathode or negative electrode and an anode or positive electrode...
may be used on the material to induce effects such as chain scission (which makes the polymer chain shorter) and
cross linkingCross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...
. The result is a change in the properties of the polymer which is intended to extend the range of applications for the material. The effects of irradiation may also include changes in
crystallinityCrystallinity refers to the degree of structural order in a solid. In a crystal, the atoms or molecules are arranged in a regular, periodic manner. The degree of crystallinity has a big influence on hardness, density, transparency and diffusion. In a gas, the relative positions of the atoms or...
as well as
microstructureMicrostructure is defined as the structure of a prepared surface or thin foil of material as revealed by a microscope above 25X magnification . The microstructure of a material can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high /...
. Usually, the irradiation process
degrades the polymerPolymer degradation is a change in the properties - tensile strength, colour, shape, etc - of a polymer or polymer based product under the influence of one or more environmental factors such as heat, light or chemicals...
. The irradiated polymers may sometimes be characterized using
DSCDifferential scanning calorimetry or DSC is a thermoanalytical technique in which the difference in the amount of heat required to increase the temperature of a sample and reference are measured as a function of temperature. Both the sample and reference are maintained at nearly the same...
,
XRDX-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and diffracts into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture...
,
FTIRFourier transform spectroscopy is a measurement technique whereby spectra are collected based on measurements of the coherence of a radiative source, using time-domain or space-domain measurements of the electromagnetic radiation or other type of radiation....
, or SEM.
In poly(vinylidene fluoride-trifluoroethylene) copolymers, high-energy electron irradiation lowers the energy barrier for the ferroelectric-paraelectric phase transition and reduces polarization hysteresis losses in the material .
See also
- Electron beam lithography
Electron beam lithography is the practice of scanning a beam of electrons in a patterned fashion across a surface covered with a film , and of selectively removing either exposed or non-exposed regions of the resist...
- Beta Particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
- Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted. In the case of electron emission, it is referred to as beta minus , while in the case of a positron emission as beta plus...
- Sterilization (microbiology)
Sterilization refers to any process that effectively kills or eliminates transmissible agents from a surface, equipment, article of food or medication, or biological culture medium. Sterilization does not, however, remove prions...