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2 Types of Radiation and Their Properties
to a wavelength of about 250 nm, which is solidly in the ultraviolet (UV). Thus, any
photon radiation that is more energetic (shorter wavelength) than UV will be ionizing,
while visible light and longer-wavelength radiation (including radio frequencies) is
non-ionizing.
In addition to high-energy photons, ionizing radiation also includes charged particles (alpha and beta radiation) and uncharged particles (neutrons). Each type of radiation has its own physical properties that affect the manner in which it interacts with
matter and within our bodies and that determines the instrument(s) used for detection
as well as our radiation safety practices. These are described in more detail below.
2.1.1 Alpha Radiation
Alpha particles are relatively massive charged particles given off by heavy and
unstable atoms. Alpha radiation is very damaging to living cells because of its relatively high mass and electrical charge. These same factors cause alpha radiation to
lose energy quickly in tissue, with the result that alpha radiation cannot penetrate
more than several microns into tissue; less than the thickness of the dead cells of the
epidermis. Thus, as long as alpha radiation is neither inhaled or ingested and as long
as open cuts and scrapes are covered, alpha radiation is harmless. Internally, however,
alpha radioactivity is highly dangerous; the Russian spy Alexander Litvenenko was
killed by ingesting very small amounts of alpha-emitting polonium (Po-210)—about
as much as a single grain of salt. While there is no need for protective equipment to
avoid tissue damage, protective clothing will prevent skin contamination that might
later transfer to food or to other objects. In addition, respiratory protection will reduce
the risk of accidental inhalation and covering open cuts, scrapes, and other injuries
will reduce the risk of absorption into the blood stream.
Table 2.1 summarizes some important information about alpha radiation.
2.1.2 Beta Radiation
Beta particles are electrons or positrons—small, light particles—given off by radioactive atoms. Any element can have nuclides that give off beta radiation. Beta radiation
is less damaging to living cells than alpha radiation, but beta particles penetrate more
deeply into human tissue—up to about 1 cm. Accordingly, external beta radiation
cannot damage internal organs, but high levels of beta contamination can produce
skin burns (“beta burns”) unless decontaminated quickly. Heavy clothing (e.g. firefighters’ turnout gear and heavy gloves) will protect the skin from most beta radiation,
and workers should wear respiratory protection if beta-emitting radioactivity might
be airborne.
While beta radiation is normally in the form of negatively charged electrons,
some neutron-deficient radionuclides emit positrons—the antimatter equivalent of
2 Types of Radiation and Their Properties
to a wavelength of about 250 nm, which is solidly in the ultraviolet (UV). Thus, any
photon radiation that is more energetic (shorter wavelength) than UV will be ionizing,
while visible light and longer-wavelength radiation (including radio frequencies) is
non-ionizing.
In addition to high-energy photons, ionizing radiation also includes charged particles (alpha and beta radiation) and uncharged particles (neutrons). Each type of radiation has its own physical properties that affect the manner in which it interacts with
matter and within our bodies and that determines the instrument(s) used for detection
as well as our radiation safety practices. These are described in more detail below.
2.1.1 Alpha Radiation
Alpha particles are relatively massive charged particles given off by heavy and
unstable atoms. Alpha radiation is very damaging to living cells because of its relatively high mass and electrical charge. These same factors cause alpha radiation to
lose energy quickly in tissue, with the result that alpha radiation cannot penetrate
more than several microns into tissue; less than the thickness of the dead cells of the
epidermis. Thus, as long as alpha radiation is neither inhaled or ingested and as long
as open cuts and scrapes are covered, alpha radiation is harmless. Internally, however,
alpha radioactivity is highly dangerous; the Russian spy Alexander Litvenenko was
killed by ingesting very small amounts of alpha-emitting polonium (Po-210)—about
as much as a single grain of salt. While there is no need for protective equipment to
avoid tissue damage, protective clothing will prevent skin contamination that might
later transfer to food or to other objects. In addition, respiratory protection will reduce
the risk of accidental inhalation and covering open cuts, scrapes, and other injuries
will reduce the risk of absorption into the blood stream.
Table 2.1 summarizes some important information about alpha radiation.
2.1.2 Beta Radiation
Beta particles are electrons or positrons—small, light particles—given off by radioactive atoms. Any element can have nuclides that give off beta radiation. Beta radiation
is less damaging to living cells than alpha radiation, but beta particles penetrate more
deeply into human tissue—up to about 1 cm. Accordingly, external beta radiation
cannot damage internal organs, but high levels of beta contamination can produce
skin burns (“beta burns”) unless decontaminated quickly. Heavy clothing (e.g. firefighters’ turnout gear and heavy gloves) will protect the skin from most beta radiation,
and workers should wear respiratory protection if beta-emitting radioactivity might
be airborne.
While beta radiation is normally in the form of negatively charged electrons,
some neutron-deficient radionuclides emit positrons—the antimatter equivalent of