Tab C

                        Radiation Glossary

                                                    
Prepared: May 11, 1994
RADIATION GLOSSARY1

Absolute risk.  An expression of excess risk based on the
assumption that the excess risk from radiation exposure adds to the
underlying (baseline) risk by an increment dependent on dose but
independent of the underlying natural risk.

Absorbed dose.  The mean energy imparted by ionizing radiation to
an irradiated medium per unit mass. Units: gray (Gy), rad.

Activity.  The mean number of decays per unit flame of a
radioactive nuclide. Units: Becquerel (Bq), Curie (Ci),

Additive interaction model (AIM). The assumption that the total
risk from exposure to radiation and to another risk factor is equal
to the sum of the excess risks from the two taken separately.

Adenocarcinoma.  A carcinoma derived from gland-forming tissues in
which the tumor cells form recognizable gland-like structures when
seen microscopically.

Alpha particle.  Two neutrons and two protons bound as a single
particle that is emitted from the nucleus of certain radioactive
isotopes in the process of decay or disintegration.

Aneuploid.  Having numbers of chromosomes not equal to exact
multiples of the haploid number.

Background radiation. The amount of radiation to which a member of
the population is exposed from natural sources, such as terrestrial
radiation due to naturally occurring radionuclides in the soil,
cosmic radiation originating in outer space, and naturally
occurring radionuclides deposited in the human body.

Baseline rate.  The cancer experience observed in a population in
the absence of the specific agent being studied; the baseline rate
might however, include cancers from a number of other causes, such
as smoking, background radiation, etc.

Becquerel (Bq). SI unit of activity. (See Units)

BE[R III.  Refers to the third National Research Council's
Committee on Biological Effects of Ionizing Radiation, as well as
to the report published by the Committee in 1980.

     1Taken from the fifth report of the National Research
Council's Committee on Biological Effects of Ionizing Radiation
(BIERV), pages 391-399, with minor modification.
Beta particle.  A charged particle emitted from the nucleus of
certain unstable atomic nuclei (radioactive elements), having the
charge and mass of an electron.

Brachytherapy.  Treatment with ionizing radiation whose source us
directly applied to the body or is located only a very short
distance from the tissue being treated.

Cancer.  A malignant tumor of potentially unlimited growth, capable
of invading surrounding tissue and/or spreading to other parts of
the body by metastasis.

Carcinogen  An agent that may cause cancer. Ionizing radiations are
physical carcinogens; there are also chemical and biological
carcinogens; biological carcinogens may be external (e.g., viruses)
or internal (genetic defects).

Carcinoma.  A malignant tumor (cancer) of epithelial cell origin.

Case-control study. An epidemiological study in which people with
disease and a similarly composed group of people without disease
are compared in terms of exposures to a putative causative agent.

Cell culture.  The growing cells in vitro (a glass container) in
such a manner that the cells are no longer organized into tissues.

Chromosomal nondisjunction.  Either a gain or a loss of chromosomes
that occurs when cell division leading to either egg or sperm
production goes awry. This results in aneuploidy.

Cohort study.  Or follow-up study; an epidemiological study in
which groups of people are identified with respect to the presence
or absence of exposure.to a disease-causing agent and the outcomes
in terms of disease rates are compared.

Competing risks.  Other causes of death which affect the value of
the risk being studied. Persons dying of other causes are not at
risk of dying from the factor in question.

Confidence interval.  A measure of the reliability of a risk
estimate. A 90% confidence interval means that 9 times out of 10
the estimated risk would be within the specified interval.

Curie. (Ci).  A unit of activity equal to 3.7 x 10 10
disintegrations/sec. (see Units)

DNA. Deoxyribonucleic acid; the genetic material of cells.

Dominant mutation.  The mutation is dominant if it produces its
effects in the presence of an equivalent normal gene from the other
parent.

Dose.  See absorbed dose.                                     
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Dose-distribution factor.  A factor which accounts for modification
of the dose effectiveness in cases in which the radionuclide
distribution and the resultant dose are nonuniform.

Dose-effect (dose-response) model.  A mathematical formulation of
the way the effect (or biological response) depends on dose.

Dose equivalent  A quantity that expresses, for the purposes of
radiation protection and control, an assumed equal biological
effectiveness of a given absorbed dose on a common scale for all
kinds of ionizing radiation. SI unit is the Sievert. (see Units)

Dose rate. The quantity of absorbed dose delivered per unit time.

Dose Rate Effectiveness Factor (DREF).  A factor by which the
effect caused by a specific dose of radiation changes at low as
compared to high dose rates.

Doubling dose.  The amount of radiation needed to double the
natural incidence of a genetic or somatic anomaly.

Electron volt. (eV).  A unit of energy = 1.6 x 10 12 ergs-l.6 x 10
19 J; l eV is equivalent to the energy gained by an electron in
passing through a potential difference of 1 V; 1 keV-1,000 eV;
lMeV-l,000,000 eV.

Epidemiology.  The study of determinants of the frequency of
disease In man. The two main types of epidemiological studies of
chronic disease are cohort (or follow-up) studies and case control
(or retrospective) studies.

Etiology. The science or description of cause(s) of disease.

Euploid.  Having uniform exact multiples of the haploid number of
chromosomes.

Fallout.  Radioactive debris from a nuclear detonation or other
source, usually deposited from air-borne particles.

Fluoroscopy.  A method of visualizing internal structures by
directing x-rays through an object (e.g., part of the body) onto a
fluorescent screen.

Fractionation.  The delivery of a given total dose of radiation as
several smaller doses, separated by intervals of time.

Gamma radiation.  Also gamma rays; short wavelength electromagnetic
radiation of nuclear origin, similar to x rays but usually of
higher energy (100 keV to 9 MeV).

Geometric mean.  The geometric mean of a set of positive numbers is
the exponential of the arithmetic mean of their logarithms. The
geometric mean of a lognormal distribution is the exponential of
the mean of the associated normal distribution.

Geometric standard deviation (GSD). The geometric standard
deviation of a lognormal distribution is the exponential of the
standard deviation of the associated normal-distribution.

Gray (Gy).  SI unit of absorbed dose. (see Units)

Half-life, biologic.  Time required for the body to eliminate half
an administered dose of any substance by regular processes of
elimination; it is approximately the same for both stable and
radioactive isotopes of a particular element.  

Half-life, radioactive.  Time required for a radioactive substance
to lose 50% of its activity by decay.

ICDA.  The International Classification of Disease Adapted for use
in the U.S. The ICD is periodically revised by the World Health
Organization; the 8th ICDA is adapted from the 8th ICD and was
issued in 1972.

Incidence.  Or incidence rate; the rate of occurrence of disease
within a specified period of time, often expressed as number of
cases per 100,000 individuals per year.

In utero.  in the womb, i.e., before birth.

In vitro.  (Literally, in glass), in culture or in the test-tube
(as opposed to in vivo, in the living individual).

In vivo.  In the living organism.

Ionizing radiation.  Radiation sufficiently energetic to dislodge
electrons from an atom. Ionizing radiation includes x and gamma
radiation, electrons (beta radiation), alpha particles (helium
nuclei), and heavier charge atomic nuclei. Neutrons ionize
indirectly by colliding with atomic nuclei.

Isotopes.  Nuclides that have the same number of protons in their
nuclei, and hence the same atomic number, but that differ in the
number of neutrons, and therefore in the mass number; chemical
properties of isotopes of a particular element are almost
identical.

Kerma Kinetic Energy Released in Material.  A unit of exposure
expressed in rad, that represents the kinetic energy transferred to
charged particles per unit mass of irradiated medium when
indirectly ionizing (uncharged) particles, such as photons or
neutrons, traverse the medium. If all of the kinetic energy is
absorbed "locally", the Kerma is equal to the absorbed dose.

Laten period.  The period of time between exposure and expression
of the disease. After exposure to a dose of radiation, there is a
delay in several years (the minimum latent period) before any
cancers are seen.

Leukemia.  A malignant disease of the white blood cells and their
precursors.

Life-span study (LSS). Life-span study of the Japanese atomic-bomb
survivors; the sample consists of 120,000 persons, of whom 82,000
were exposed to the bombs, mostly at low doses.

Life table.  A table showing the number of persons who, of a given
number born or living at a specified age, live to attain successive
higher ages, together with the numbers who die in each age
interval.

Linear energy transfer (LET).  Average amount of energy lost per
unit track length.

       Low LET. Radiation characteristic of light charged particles
such as electron produced by x rays and gamma rays where the
distance between ionizing events is large on the scale of a
cellular nucleus.

       High LET  Radiation characteristic of heavy charged
particles such as protons and alpha particles where the distance
between ionizing events is small on the scale of a cellular
nucleus.

Linear (L) model. Also, linear dose-effect relationship; expresses
the effect (e.g.', mutation or cancer) as a direct (linear)
function of dose.

Linear-quadratic (LQ) model. Also, linear-quadratic dose-effect
relationship; expresses the effect (e.g., mutation or cancer) as
partly directly proportional to the dose (linear term) and partly
proportional to the square of the dose (quadratic term). The linear
term will predominate at lower doses, the quadratic term at high
doses.

Lymphoma.      A general term for any neoplastic disorder of the
lymphoid tissues.

Monosomy.      The absence of one chromosome from the complement of
an otherwise diploid cell.

Monte Carlo Calculation.  The evaluation of probability
distribution by means of random sampling.

Mortality (rate).  The rate to which people die from disease, e.g.,
a specific type of cancer, often expressed as number of deaths per
100,000 per year.
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Multiplicative interaction model (MIM).  The assumption that the
relative risk (the relative risk plus one) resulting from the
exposure to two risk factors is the product of the relative risks
from the two factors taken separately.

Neoplasms.  Any new and abnormal growth, such as a tumor;
neoplastic disease refers to any disease that forms tumors, whether
malignant or benign.

Neutron.  Uncharged subatomic particle capable of producing
ionization in matter by collision with charged particles.

Nonstochastic.  Describes effects whose severity is a function of
dose; for these, a threshold may occur; some nonstochastic somatic
effects are cataract induction, nonmalignant damage to the skin,
hematological deficiencies, and impairment of fertility.

Nuclide.  A species of atom characterized by the constitution of
its nucleus, which is specified by its atomic mass and atomic
number (Z), or by its number of protons (Z), number of neutrons
(N), and energy content.

Oncogeny  Genes that carry the potential for cancer.

Person-gray.  Unit of population exposure obtained by summing
individual dose-equivalent values for all people in the exposed
population. Thus, the number of persons-gray contributed by 1
person exposed to l Gy is equal to that contributed by 100,000
people each exposed to 10 uGy.

Person-years-at-risk (PYAR).  The number of persons exposed times
the number of years after exposure minus some lag period during
which the dose is assumed to be unexpressed (minimum latent
period.)

Prevalence.  The number of cases of a disease in existence at a
given time per unit population, usually 100,000 persons.

Probability of causation.  A number that expresses the probability
that a given cancer, in a specific tissue, has been caused by a
previous exposure to a carcinogenic agent, such as radiation.

Progeny.  The decay products resulting after a series of
radioactive decay. Progeny can also be radioactive, and the chain
continues until a stable nuclide is formed.

Projection model.  A mathematical model that simultaneously
described the excess cancer risk at different levels of some factor
such as dose, time after exposure, or baseline level of risk, in
terms of a parametric function of that factor.  It becomes a
projection model when data in a particular range of observations is
used to assign values to the parameters in order to estimate (or
project) excess risk for factor values outside that range.

Promoter.  An agent which is not by itself carcinogenic, but which
can amplify the effect of a true carcinogen by increasing the
probability of late-stage cellular changes needed to complete the
carcinogenic process.

Protraction.  The spreading out of a radiation dose over time by
continuous delivery at a lower dose rate.

Quadratic-dose model.  A model which assumes that the excess risk
is proportional to the square of the dose.

Quality factor (Q).  A, LET dependent factor by which absorbed
doses are multiplied to obtain (for radiation-protection purposes)
a quantity which corresponds more closely to the degree of
biological effect produced by x or low-energy gamma rays. Dose in
Gy x Q = Dose equivalent in Sv.

Rad.  A unit of absorbed dose.  Replaced by the gray in SI units.
(see Units)

Radioactivity.  The property of some nuclides of spontaneously
emitting particles or gamma radiation, emitting x radiation after
orbital electron capture, or undergoing spontaneous fission.

       Artificial radioactivity.  Man-made radioactivity produced
by fission, fusion, particle bombardment, or electromagnetic
irradiation.

       Natural radioactivity. The property of radioactivity
exhibited by more that 50 naturally occurring radionuclides.

Radiogenic.  Cause by radiation.

Radioisotopes.  A radioactive atomic species of an element with the
same atomic number and usually identical chemical properties.

Radionuclides.  A radioactive species of an atom characterized by
the constitution of its nucleus.

Radiosensitivity. Relative susceptibility of cells, tissues,
organs, and organisms to the injurious action of radiation;
radiosensitivity and its antonym, radioresistance, are used in a
comparative sense rather than an absolute one.

Recessive gene disorder. This requires that a pair of genes, one
from each parent, be present in order for the disease to be
manifest.


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Relative biological effectiveness (RBE).  Biological potency of one
radiation as compared with another to produce the same biological
endpoint. It is numerically equal to the inverse of the ratio of
absorbed doses of the two radiations required to produce equal
biological effect. The reference radiation is often 200-kV x rays.

Relative risk.  An expression of excess risk relative to the
underlying (baseline) risk; if the excess equals he baseline risk
the relative risk is 2.

Rem (rad equivalent, man).  Unit of dose equivalent. The dose
equivalent in "rem" is numerically equal to the absorbed dose in
"rad" multiplied by the "quality factor" (see Quality factor), the
distribution factor and any other necessary modifying factor.

RERF (Radiation Effects Research Foundation).  A binationally
funded Japanese foundation chartered by the Japanese Welfare
Ministry under an agreement between the United States and Japan.
The RERF is the successor to the ABCC (Atomic Bomb Casualty
Commission).

Risk coefficient. The increase in the annual incidence or mortality
rate per unit dose: (l) absolute risk coefficient is the observed
minus the expected number of cases per person each year at risk for
a unit dose; (2) the relative-risk coefficient is the fractional
increase in the baseline incidence or mortality rate for a unit
dose.

Risk estimate.  The number of cases (or deaths) that are projected
to occur in a specified exposed population per unit dose for a
specified exposure regime and expression period; number of cases
per person-gray or, for radon, the number of cases per person
cumulative working-level month.

Rem. A unit of dose equivalent. Replaced by the sievert. (see
Units.)

Sarcoma.  A malignant tumor arising in the tissue of mesodermal
origin (connective tissue, bone, cartilage or striated muscle).

Sex-linked mutation (or X-linked). A mutation associated with the.X
chromosome. It will usually only manifest its effect in males (who
have only a single X chromosome).

SI units.  The International System of Units as defined by the
General Conference of Weights and Measures in 1960. These units are
generally based on the meter/kilogram/seconds units, with special
quantities for radiation including the becquerel, gray and sievert.

Sievert. The SI unit of radiation dose equivalent. It is equal to
dose in grays times a quality factor times other modifying factors,
for example, a distribution factor; 1 sievert (Sv) equals 100 rem.

Specific activity. Total activity of a given nuclide per gram of a
compound, element, or radioactive nuclide.
Specific energy.  The actual energy per unit mass deposited per
unit volume in a given event. This is a stochastic quantity as
opposed to the average value over a large number of instances
(i.e., the absorbed doses).

Spline.  A curve of predetermined shape; a spline with l knot has
a single inflection point and thus two different segments.

Squamous cell carcinoma.  A cancer composed of cells that are scaly
or platelike, resembling the skin surface.

Standard mortality ratio (SMR).  Standard mortality ratio is the
ratio of the disease or accident mortality rate in a certain
specific population compared with that in a standard population.
The ratio is based on 100 for the standard so that an SMR of 200
means that the test population has twice the mortality from that
particular cause of death.

Stochastic. Random events leading to effects whose probability of
occurrence in a exposed population (rather than severity in an
affected individual) is a direct function of dose; these effects
are commonly regarded as having no threshold; heredity effects are
regarded as being stochastic; some somatic effects, especially
carcinogens, are regarded as being stochastic.

Target theory (hit theory).  A theory explaining some biological
effects of radiation on the basis that ionization, which occurs in
a discrete volume (the target) within the cell, directly causes a
lesion that later results in a physiological response to the damage
at that location; one, two, or more hits (ionizing events within
the target) may be necessary to elicit the response.

Teletherapy.  Treatment with ionizing radiation whose source is
some distance from the tissues being treated.

Threshold hypothesis.  The assumption that no radiation injury
occurs below a specified dose.

Time-since-exposure (TSE) model. A model in which the risk is not
constant but varies with the time after exposure.

Transformed cells.  Tissue culture cells changed in vitro from
growing in an orderly pattern and exhibiting contact inhibition to
growing in a pattern more like that of cancer cells, due to the
loss of contact inhibition.

Translocation.  A chromosome aberration resulting from chromosome
breakage and subsequent structural rearrangement of the parts
between the same of different chromosome.

Trisomy.  The presence of an additional (third) chromosome of one
type in an otherwise diploid cell.

Tumorigenicity.  Ability of cells to proliferate into tumors when
inoculated into a specified host organism under specified
conditions

Units*                   Conversion Factors

Becquerel (SI)      1 disintegration/s = 2.7 x 10 11 Ci
Curie               3.7 x 10 10 disintegration/s = 3.7 x 10 10 Bq
Gray (SI)           1 J/kg - 100 rads
Rad                 100erg/g-0.01 Gy
Rem                 0.01 Sievert
Sievert(SI)         100 rem

       *International Units are designated SI.

UNSCEAR.  United Nations Scientific Committee on the Effects of
Atomic Radiation publishes periodic reports on sources and effects
of ionizing radiation.

X radiation. Also x rays; penetrating electromagnetic radiation,
usually produced by bombarding a metallic target with fast
electrons in a high vacuum.


  


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