Alpha particles are positively charged particles made up of two protons and two
neutrons. The particles lose their energy quickly and do not penetrate the surface of the
skin if the body is exposed externally. Material containing alpha radioactivity can enter
the body through a cut in the skin, by ingestion, or inhalation. Uranium-238 and
plutonium-239 are sources of alpha radiation. [Back to Module
2]
BEIR V
The latest National Research Council Committee on Biological Effects of Ionizing
Radiations is known as BEIR V. The committee's report is Health Effects of Exposure to Low
Levels of Ionizing Radiation. [Back to Module 2]
BETA PARTICLES
Beta particles are fast moving electrons which are negatively charged. Beta radiation
can penetrate a few millimeters in human tissue before losing all of its energy.
Iodine-131, phosphorus-32, and strontium-90 are all sources of beta radiation. [Back to Module 2]
CURIE
This is a measure of radioactive material. It measures the number of atoms that decay
each second. One curie is 37 billion atoms undergoing decay each second. Hanford released
an estimated 739,000 curies of iodine-131 from 1944 to 1972. In contrast, the 1979
accident at the Three Mile Island nuclear power plant in Pennsylvania released an
estimated 15 curies of iodine-131. [Back to Module 2]
DOWNWINDER
Downwinder is a commonly used term which refers to people living in the pathway of
radioactive releases from a nuclear plant or from atomic bomb test sites. [Back to Module 2]
EFFECTIVE DOSE EQUIVALENT (EDE)
This term is used because a radiation dose to one part of the body does not have the
same potential health effect as a dose to another part. The EDE is used to put different
types of radiation doses on an equivalent basis in terms of their potential for causing
damage. [Back to Module 2]
EQUIVALENT DOSE
This is the measure that indicates the degree of biological damage caused by radiation.
Equivalent dose is measured in rems. [Back to Module 2]
EXTERNAL RADIATION EXPOSURE
Radiation exposure from a source outside the body is external radiation exposure. The
term refers to radiation, such as gamma rays and X-rays, that can penetrate human skin and
thus cause biological damage from outside the body. Gamma rays are photons, or
electromagnetic waves, that come from the nucleus of the atom. Gamma rays are uncharged
and pass through humans at the speed of light. As gamma rays pass through the body, they
may damage cells. Cobalt-60 is a source of gamma radiation. [Back
to Module 2]
GENETIC EFFECTS
GENETIC EFFECTS A genetic effect is the result of exposure to substances (such as
radiation) that cause damage to the genes of a reproductive cell. [Back to Module 2]
GERM CELLS
Germ cells are reproductive cells - spermatozoa and ova.
HALF-LIFE
This is the amount of time it takes for a radioactive substance to lose one-half of its
radioactivity. Iodine-131 has a half-life of eight days. At the end of eight days, half of
the iodine-131 atoms have undergone decay and converted to stable xenon-131. Half of the
remaining iodine-131 will decay into stable xenon-131 in another eight days, and so on.
When an atom decays and becomes stable, it is no longer radioactive. Some radioactive
substances decay quickly into non-radioactive materials. Others decay over long periods of
time into other radioactive materials which, in turn, undergo radioactive decay. For
example, uranium-238 has a half-life of 4.5 billion years and undergoes more than a dozen
changes before becoming a stable form of lead. [Back to Module
2]
INTERNAL RADIATION EXPOSURE
Internal radiation exposure occurs when a radioactive substance is taken into the body
by eating, drinking, or breathing. [Back to Module 5]
IONIZING RADIATION
The types of radiation capable of removing one or more electrons from atoms they
encounter, leaving positively charged particles such as alpha and beta, and
non-particulate forms such as X-rays and gamma radiation. Ionizing radiation may damage
human cells. Non-ionizing radiation includes visible, ultraviolet, and infrared light, as
well as radio waves. [Back to Module 2]
ISOTOPES
Different forms of the same chemical element, which have different numbers of neutrons
but the same number of protons in the nucleus of their atoms, are called isotopes. A
single element may have many isotopes. For example, stable iodine is iodine-127. Its
radioactive isotopes include iodine-129 and iodine-131. [Back
to Module 2]
LATENT PERIOD
The time between exposure to radiation and the appearance of a delayed effect is the
latent period. [Back to Module 2]
ORGAN DOSE
Among the factors to consider in measuring radiation dose is whether a person received a
radiation dose to a single organ or to the whole body. For example, when iodine-131 enters
the body, it mainly concentrates in the thyroid gland and gives a dose to this organ.
RAD
A rad is a unit used to measure the absorbed dose, or the amount of energy body tissues
absorb. However, equal doses of different types of radiation may not have the same effects
on the body. For instance, a dose of alpha particles is more damaging than the same dose
of gamma rays or beta particles. [Back to Module 2]
RADIATION DOSE
The amount of radiation, or energy, absorbed by a person is called a dose. Units of dose
are used to describe the potential for radiation damage to body tissues. [Back to Module 2]
RADIOISOTOPE
The radioactive isotope of an element that has all the chemical properties of the stable
form of the element is a radioisotope. The radioisotope undergoes radioactive decay.
RADIONUCLIDE
An unstable form of an element that can decay and give off radiation is a
radionuclide.
Radionuclide is the same as radioisotope. [Back to Module
2]
REM
The rem is the unit of radiation accounting for the different effects of different types
of radiation. In order to calculate the equivalent dose in rem, absorbed dose must first
be established. This number is then multiplied by a radiation weighting factor depending
on the type of radiation. For beta particles and gamma rays, the weighting factor is 1.
Most of the radioactive material released from Hanford emit beta particles and/or gamma
rays, so it is easy to convert directly from rad to rem: 1 rad is equal to 1
rem. Doses
from alpha particles and neutrons have larger weighting factors. [Back to Module 2]
SOMATIC EFFECTS
The effects of radiation exposure that result from damage to non-reproductive cells are
somatic effects. If the number of cells which suffer somatic effects is great enough, then
the damage becomes clinically observable.
SOURCE TERM
Source term refers to the amount and type of radioactive material released into the
environment. [Back to Module 6]
WHOLE BODY DOSE
Radiation exposure to gamma rays and X-rays from outside the body can give a radiation
dose to the entire body, and each organ receives approximately the same dose. Some
internal exposure also gives a whole-body dose. Tritium, for example, is a form of
hydrogen. Since hydrogen is part of water molecules which are present throughout the body,
tritium delivers a dose to all tissues.
X-RAYS
X-rays are similar to gamma rays but are produced outside the nucleus. Their properties
are identical to those of gamma rays. [Back to Module 2]
