- Exposure of a sample or object to nuclear or short-wavelength electromagnetic
radiation, usually for a definite
purpose. Biological and pharmaceutical materials may have their properties
altered by exposure to ultraviolet radiation;
X-rays are widely used in medicine and
industry. Materials may be irradiated directly with radiation of a given
type and energy by placing them in a particle accelerator
or nuclear reactor, but it is
often more practical to use the radiation from manufactured radioactive
isotopes to change their physical and
chemical properties as required. Neutrons
and gamma rays are used to sterilize
foodstuffs and control the reproduction of insect pests.
The outer layers of a supernova are
irradiated by neutrons produced as the core collapses to form a neutron
star; these neutrons react with atomic nuclei to form heavier elements.
See also ionizing radiation.
AND NUCLEAR PHYSICS
- An optical effect of contrast that
makes bright objects viewed against a dark background appear to be larger
than they really are.