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OCR for page 577
Glossary
Absorbed dose. The mean energy imparted to the irradiated medium,
per unit mass, by ionizing radiation. Units: gray (Gy), red.
Activity. The mean number of decays per unit time of a radioactive
nuclide. Units: becquere! (Bqj, curie (Ci).
Activity median aerodynamic diameter (AMAD). The diameter of a
unit-density sphere with the same terminal settling velocity in
air as that of the aerosol particulate whose activity is the median
for the entire aerosol.
Additive interaction model. This model is used to find the combined
risk for risk factors which have no interaction with each other.
For example, the combined mortality risk of cigarette smoking
and automobile accidents is the sum of the separate risks.
Adenosarcoma. A mixed tumor which consists of a substance like
embroyonic connective tissue together with glandular elements.
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. Down syndrome is an example.
Background radiation. Radiation arising from radioactive material
other than that under consideration; background radiation due
to cosmic rays and natural radioactivity is always present; there
may also be background radiation due to the presence of radioac-
tive substances in building material.
577
OCR for page 578
578
GLOSSARY
Bayesian analysis. Analysis in which Bayes' theorem is used to derive
posterior probabilities from assumed prior knowledge together
with observational data. For example, biological information on
the relationship between species and hazardous substances can
be combined with data on interspecies dose response to calculate
the response of human populations.
Becquerel (Bq). SI unit of activity. (See Units.)
Bremsstrahiung. The production of electromagnetic radiation (pho-
tons) by the acceleration (positive or negative) that a fast,
charged particle (usually an electron) undergoes from the ef-
fect of an electric or magnetic field; for instance, from the field
of another charged particle (usually a nucleus).
Bronchioles. The small branches of the tracheobronchial tree of the
Jung.
Cell culture. The growing of cells in vitro, in such a manner that the
ceils 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.
Ciliated mucosa. The mucous membrane in the lung covered with
small hairlike structures which serve to move the mucus.
Competing risks. Other causes of death which affect the value of the
risk being studied. Persons dying from other causes are not at
risk of dying from the factor in question.
Constant-relative-risk model. A risk mode} which assumes that, after
a certain time, the ratio of the risk at a specific dose to the risk
in the absence of the dose does not change with time.
Contact inhibition. The cessation of migratory activity and some-
times other functions, including mitosis, when adjacent cells
establish firm contact.
Con proportional hazards model. A relative-risk mode! that permits
the use of internal comparison groups as controls for confounding
variables such as cigarette smoking and age.
Curie (Ci). A unit of activity equal to 3.7 x 10~° disintegrations/s.
(See Units.)
Daughter product. An isotope formed as a result of radioactive decay.
One daughter atom is formed for each particle emitted.
OCR for page 579
GLOSSARY
579
Decay chain or decay series. A sequence of radioactive decays of
the same nucleus. An initial nucleus, the parent, decays into a
daughter nucleus that differs from the first by whatever particles
were emitted during the decay. If further decays take place, the
subsequent nuclei are also usually called daughters. Sometimes,
to distinguish the sequence, the daughter of the first daughter is
called the granddaughter, etc.; ordinarily, however, this quickly
becomes too complicated.
Diffusion. The random path followed by very small particles due
to the impact of surrounding molecules. This Brownian motion
governs the transport of submicrometer-size particles in air.
Dominant mutation. The mutation is dominant if it produces its
effect in the presence of an equivalent normal gene from the
other parent.
Dose-distribution factor. A factor which accounts for modification of
the dose effectiveness in cases in which the radionuclide distri-
bution is nonuniform.
Dose equivalent. A quantity that expresses, for the purposes of
radiation protection and control, the assumed effectiveness of
dose on a common scale for all kinds of ionizing radiation. ST
unit is the Sievert. (See Units.)
Doubling dose. The amount of radiation needed to double the natural
incidence of a genetic or somatic anomaly.
Electron volt (egg. A unit of energy = 1.6 x 1o-~2 ergs = 1.6 x
10-~9 J; 1 eV is equivalent to the energy gained by an electron
in passing through a potential difference of 1 V; 1 keV = 1,000
eV; 1 MeV = 1,000,000 eV.
Epithelium. A membranous cellular tissue that covers the surface of
some organ or part of the body.
Equilibrium fraction. In equilibrium, the parents and daughters have
equal radioactivity, that is, as many decay into a specific nucTide
as decay out. When fresh radon enters a volume, the daughter
products have not yet accumulated, and there IS disequilibrium.
The working-level definition of radon does not take into account
the amount of equilibrium.
Equilibrium, radioactive secular. The condition in which the activities
of a parent and daughter in a radioactive decay chain are (very
nearly) equal.
OCR for page 580
580
GLOSSARY
Equilibrium, radiation. The condition in a radiation field where the
energy of the radiations entering a volume equals the energy of
the radiations leaving that volume.
Euploid. Having uniform exact multiples of the haploid number of
chromosomes.
Gamma ray. Short-wavelength electromagnetic radiation of nuclear
origin (range of energy, 10 keV to 9 MeV).
Gray (Gy). ST unit of absorbed dose. (See Units.)
Half-life, biologic. Time required for the body to eliminate half of
an administered dose of any substance by regular processes of
elimination; it is approximately the same for both stable en c!
radioactive isotopes of a particular element.
Half-life, radioactive. Time required for a radioactive substance to
lose 50~o of its activity by decay.
impaction. As air is taken into the Jung, it follows a tortuous path,
changing direction many times. At each change of direction,
the momentum of the particles carried in the airstream causes
them to impact on the bifurcations of the lung. The force on
the particle causing it to move and impact on the lung surface is
the Stokes force, which is proportional to the velocity of the air
moving with respect to the particle. Impaction is important for
particles with large aerodynamic diameters.
Incidence. The rate of occurrence of a disease within a specified
period; usually expressed in number of cases per 100,000 persons
per year.
Ionization. The process by which a neutral atom or molecule acquires
a positive or negative charge.
ionization density. Number of ion pairs per unit volume.
ionization path (track). The trail of ion pairs produced by ioniz-
ing radiation in its passage through matter.
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 enutrons, and therefore in the mass number;
chemical properties of osotopes of a particular element are almost
identical. The term should not beused as a synonym for nuclide.
OCR for page 581
GLOSSARY
581
Latent period;. The period of time between exposure and expression
of the disease. After exposure to a dose of radiation, there is a
delay of several years (the latent period) before any cancers are
seen.
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.
Lifetime risk. The lifetime probability of dying of a specific disease.
Lifetime risk ratio. The ratio of the lifetime risk (Re) of an exposed
person to the lifetime risk of an unexposed person (Ro). This
number minus 1 is the proportional increased risk associated
with exposure (Re - Ro).
Linear dose model. This mode} postulates that the excess risk is
linearly proportional to the dose.
Linear energy transfer fLET9. Average amount of energy lost per
unit track length.
Low LET. Radiation characteristic of electrons, x rays, and
gamma rays; the distance between ionizing events is large on
the scale of a cellular nucleus.
High [ET. Radiation characteristic of protons and fast neutrons;
the distance between ionizing events is small on the scale of a
cellular nucleus. Average LET is specified to even out the effect
of a particle that is slowing down near the end of its path and to
allow for the fact that secondary particles are not all of the same
energy.
Lymphosarcoma. A sarcoma of the lymphoid tissue. This does not
include Hodgkin's disease.
Minute volume. The amount of air moving through the Jung per
minute; the product of the breathing rate times the volume of
air per breath.
Multiplicative interaction model. A mode! in which independent risk
factors interact so that the combined risk is the product of the
relative risks due to each factor alone.
Neoplasms. Any new and abnormal growth, such as a tumor; neo-
plastic disease refers to any disease that forms tumors, whether
malignant or benign.
Nonstochastic. Describes effects whose severity is a function of dose;
for these, a threshold may occur; some nonstochastic somatic
OCR for page 582
582
GLOSSARY
ejects are cataract induction, nonmalignant damage to 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.
Oncogenes. Genes which carry the potential for cancer.
Person-gray. Unit of population exposure obtained by suIruning
individual dose-equivalent values for all people in the exposed
population. Thus, the number of person-grays contributed by 1
person exposed to 1 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 (latent period).
Prevalence. The number of cases of a disease in existence at a given
time per unit population, usually 100,000 persons.
Progeny. The decay products resulting after a series of radioactive
decays. Progeny can also be radioactive, and the chain continues
until a stable nuclide is formed.
Quadratic-dose model. A mode! which assumes that the excess risk
is proportional to the square of the dose.
Quality factor (Q}. A linear energy transfer 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.
Rad. A unit of absorbed dose. Replaced by the gray in SI units. (See
Units.)
Radioactivity. The property of some nuclides of spontaneously emit-
ting particles or gamma radiation, emitting x radiation after
orbital electron capture, or undergoing spontaneous fission.
ATtipCia' Ta~ioaCtiVit9. Man-made radioactivity produced by
fission, fusion, particle bombardment, or electromagnetic irradi-
ation.
Natural radioactivity. The property of radioactivity exhibited by
more than 50 naturally occurring radionuclicles.
OCR for page 583
GLOSSARY
583
Radioisotopes. A radioactive atomic species of an element with the
same atomic number and usually identical chemical properties.
Radionuclide. 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.
An example is cystic fibrosis.
Relative biological effectiveness (RBE). Biological potency of one ra-
diation 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 mutation risk. The ratio of the risk of a genetic mutation
among the exposed population to that in the absence of exposure.
Risk coefficient. The increase in the annual incidence or mortality
rate per unit dose: (1) absolute risk coefficient is the observed
minus the expected number of cases per person 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
defined 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.)
Sedimentation. The gravitational force on a particle is partially
balanced by the viscous force of the air. The resultant velocity
toward the earth is the sedimentation velocity. Important for
particles with intermediate aerodynamic diameters.
Sex-linked mutation (OT X-linked). A mutation associated with the
X chromosome. It will usually only manifests its effect in males
(who have only a single X chromosome).
S] 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/second units, with spe-
cial quantities for radiation including the becquerel, gray, and
sievert.
OCR for page 584
584
GLOSSARY
Sievert. The ST unit of radiation dose equivalent. It ~ equal to dose
in grays times a quality factor times other modifying factors, for
example, a distribution factor; 1 sievert 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 dose).
Squamous cell carcinoma. A cancer composed of cells that are scaly
or platelike.
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. Describes random events leading to effects whose proba-
bility of occurrence in an exposed population (rather than sever-
ity in an affected individual) is a direct function of dose; these
effects are commonly regarded as having no threshold; hereditary
effects are regarded as being stochastic; some somatic effects, es-
pecially carcinogenesis, are regarded as being stochastic.
Stopping power. The average rate of energy loss of a charged particle
per unit thickness of a material or per unit mass of material
traversed.
Straggling. The statistical variation in the range of a particle caused
by the large number of interactions and scatterings within the
material being traversed.
Surface-seek~ng raclionuclide. An internal emitter that is deposited
and remains on the surface of bone for a long period of time. This
contrasts with a volume seeker, which deposits more uniformly
throughout the bone volume.
Target theory (hit theory). A theory explaining some biological effects
of radiation on the basis that ionization, which occurrs 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.
OCR for page 585
GLOSSARY
585
Threshold hypothesis. The assumption that no radiation injury oc-
curs below a specified dose.
Time-since-exposure (TSE) model. A mode} in which the relative
risk is not constant but varies with the time after exposure.
Transformed cell. 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, resulting in the loss of
contact inhibition.
Transiocation. A chromosome aberration resulting from chromosome
breakage and subsequent structural rearrangement of the parts
between the same or different chromosomes.
Tumorigenicity. Ability of cells to proliferate into tumors when inoc-
ulated into a specified host organism under specified conditions.
Unattached fraction. That fraction of the radon daughters, usually
memo (Radium A), which has not yet attached to a particle. As
a free atom, it has a high probability of being retained within
the lung and depositing alpha energy when it decays.
Units" Conversion Factors
Becquere} (SI) 1 disintegration/s = 2.7 x 10-~t Ci
Curie 3.7 x 10~° disintegrations/s = 3.7 x 10~° Bq
Gray (SI) 1 J/kg = 100 red
Rad 100 erg/g = 0.01 Gy
Rem 0.01 Sievert
Sievert (SI) 100 rem
international Units are designated (SI).
Working level (WL). Any combination of short lived radon daughters
in 1 liter of air that will result in the ultimate emission 1.3 x 105
MeV of potential alpha energy. This number was chosen because
it is approximately the alpha energy released from the decay of
daughters in equilibrium with 100 picocuries of 222Ra.
Working-leve! month (W[M}. Exposure resulting from inhalation of
air with a concentration of 1 working level of radon daughters
for 170 working hours.
Years of life lost. The expected years of life for a nonexposed person
minus the expected lifetime of an exposed person.
OCR for page 586
Representative terms from entire chapter:
lifetime risk
