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CBRN GLOSSARY AND TERMINOLOGY:
Absorbed Dose [rad]:
The rad is the unit of absorbed dose (D) measuring the energy imparted
by ionizing radiation to matter.
1 rad = .01 Joule/kilogram (or: 100 ergs/gm)
The activity of a radioactive substance is often designated by the Curie
[Ci]. The Curie is not a measure of dose; it merely states the amount of
a radioactive disintegrations per unit time. The Curie is a unit of measurement
defined as the activity of a radioactive substance disintegrating at a
rate of: 3.7 x 1010 disintegrations per second.
The philosophy inherent in any program of radiation safety is to reduce
exposure, whether internal or external, to a minimum:
"As Low As is Reasonably Achievable"
Whenever it is impossible or impractical to remove a source of radiation,
other means must be considered for purposes of personnel protection. Three
factors which determine the total exposure one receives in a given radiation
1. Time of exposure.
2. Distance from Source.
3. Amount of shielding present.
The following is an excerpt from the Federal Register / Vol 51, No.
6 / Jan 9, 1986:
Dose control terms:
(1) "ALARA" (acronym for "As low as is reasonably achievable") means
making every reasonable effort to maintain exposures to radiation as far
below the dose limits in this part as is practical: (i) Consistent with
the purpose for which the licensed activity is undertaken, (ii) taking
into account the state of technology, the economics of improvements in
relation to benefits to the public health and safety, and other societal
and socioeconomic considerations, and (iii) in relation to utilization
of nuclear energy in the public interest.
20.102 As low as is reasonably achievable levels of exposure.
(a) Each licensee shall ensure that the dose to individuals receiving
occupational doses and to members of the public is as low as is reasonably
achievable (ALARA) and does not exceed the appropriate limits.
Procedures and engineering controls based on sound radiation protection
principles and practices should be used, to the extent practical, to reduce
A positively charged nuclear particle identical with the nucleus of a helium
atom. It consists of two protons and two neutrons and is ejected at high
speed from the nucleus of an atom in certain radioactive transformations.
Alpha particles can be stopped by very thin absorbing materials, e.g.:
a few sheets of paper, or, 1/64th inch of aluminum foil. Since alpha particles
travel only short distances in air, and alpha particles up to 7.5 MeV are
absorbed by the outer layer of skin (dead tissue), alpha radiation is not
considered an external exposure problem.
Smallest particle of an element which is capable of entering into a chemical
An electron or positron ejected from the nucleus of an atom during radioactive
Though Beta particles have a greater penetration in any absorber than alpha
particles, they can still be stopped by thin absorbing materials, e.g.:
1 inch of wood, or, 1/4 inch of Lucite. However, bremsstrahlung
must be considered in shielding beta radiation: the higher the atomic number
(Z) of the absorber, the greater the percentage of bremsstrahlung. Combination
shields are effective, e.g.: for transport containers; a low-Z absorber
can be used to stop the betas, followed by a high-Z absorber to attenuate
The secondary photon radiation (X-ray)
produced by the deceleration of charged particles (especially beta
particles) as they pass through matter (from German for "braking radiation").
Deposition of radioactive material in any place where it is not desired,
particularly where its presence may be harmful.
Units of measurement (see Activity). One curie
is that quantity of a radioactive nuclide disintegrating at the rate of
3.700 x 1010 atoms per second.
Units Of Activity
||Disintegrations / Second
||3.7 x 104
||3.7 x 107
||3.7 x 10-2
The ratio of the amount of undesired radioactive material initially present
to the amount remaining after suitable processing steps have been completed.
Dose Equivalent [rem]:
The dose equivalent concept allows the scaling up of the absorbed dose
in order to better compare the effect of different types of radiation on
human systems. Dose equivalent (DE) is expressed in rem (roentgen
equivalent man) and is defined as the product of absorbed dose (D) in rads
and other necessary modifying factors.
In normal protection work the product of absorbed dose and quality
factor (QF) expresses the irradiation in terms of a common scale for all
DE = D x QF ... [rem]
Examples of QF are:
|Type of Radiation
|X-ray, gamma ray, beta particles
|Heavy recoil atoms
||2 to 10.5
DE = D x QF x DF ... [rem]
In regard to protection purposes the term QF replaces the former term
RBE (relative biological effectiveness); in order to talk about RBE one
must define exposure conditions as well as the effect studied.
Much effort has been directed toward the problem of calculating the
dose which a person receives as a result of internally deposited radionuclides.
Among the many factors of main concern that enter into such a calculation
are: the shape of the organ, the type of radiation and the distribution
of the deposit. The distribution factor (DF) is used to correct for non-uniform
distribution in the case of internally deposited radionuclides. Thus, the
dose equivalent becomes:
As a beam of photons passes through air, the interactions
which take place produce electrons, which then lose energy by creating
ion pairs. The exposure is measured by collecting these pairs. Thus, the
exposure concept is based on the ability of photons to produce ionization.
The special unit of exposure is the Roentgen [R]:
1 R = 2.58 x 10-4 Coulomb/kilogram of air
(This unit is numerically equal to the older definition for Roentgen: 1
R = 1 esu/cc of air; an exposure to X- or gamma- radiation such that the
associated corpuscular emission per 0.001293 grams of air produces, in
air, ions carrying one electrostatic unit or quantity of electricity of
Exposure Rate [R/hr]:
The exposure (X) is defined in terms of ionization produced in a volume
of air. The exposure rate is given by the quotient of exposure and time
Exposure rate = X / t... [R/hr]
The special unit of exposure rate is Roentgen
per hour, or milliroentgens:
Milliroentgen per hour: 1/1000 R/hr... [mR/hr]
A simple formula for use in Health Physics applications to estimate
the exposure rate at a distance of one meter from a known isotropic point
source of activity C [Ci] and energy E [MeV] for an energy range form .2
MeV to 2 Mev in air is:
Exposure rate = 0.53 x C x E [R/hr]
A pack of photographic film which measures radiation exposure for personnel
monitoring. The badge may contain two or three films of different sensitivity
and filters to shield parts of the film badge from certain types of radiation.
A photon emitted spontaneously from the nucleus
of an atom of a radioactive substance. It is not a particle but a form
of electromagnetic radiation, similar to light.
Geiger - Mueller Detector:
In very simple terms, the Geiger-Mueller is a metal tube that is filled
with an inert gas. There is a wire running through the center and a wire
mesh lining the inside of the tube. The mesh and the wire have opposite
applied voltages. The charges are insulated from each other by the inert
gas. When the gas is bombarded by radiation it looses its insulating properties
and allows a sudden avalanche of electron and ion flow. This is registered
as one count.
The tube then goes into a quenching mode. Basically it turns off and
returns to its normal state so that it can start over again. While the
quenching mode can be measured in milliseconds, this lag time reduces its
efficiency as compared to the scintillation detector.
Advantages of the Geiger-Mueller are that it is very rugged and inexpensive,
as compared to other detector types.
The physical or radioactive half-life is the time required for the activity
of a given isotope to decay to one-half of its initial value. In evaluating
the effects of radioactive substances deposited in the human system we
need to address two additional half-lifes:
1. The biological half-life: It is the time required for the body to
eliminate one-half of the amount of a radioactive substance internally
deposited by excretion, exhalation and perspiration.
2. The effective half-life: It is defined as the time required for the
radioactivity from a given amount of radioactive substance deposited in
the tissues or organs to diminish by 50 % as a result of the combined action
of radioactive decay and loss of the material by biological elimination.
The effective half-life is usually experimentally determined.
The half-value layer is the thickness of a substance which reduces the
intensity of a beam of radiation to one-half of its initial value. The
half-value layer is a function of the energy of the gamma and the composition
of the shield or absorber. Examples:
A science and profession devoted to the protection of man and his environment
from unnecessary radiation exposure.
Inverse Square Law:
The radiation field decreases with distance from the source. When considering
a point source in air, the decrease will follow the inverse square law,
which states that the amount of radiation at a given distance from a source
is inversely proportional to the square of the distance.
I/i = d2/D2
I x D2 = i x d2
(Where I = intensity at a distance (D) from a point source, and i =
intensity at a distance (d) from the same source).
Example: If the exposure rate at 1 meter equals 100 mR/hr then the
exposure rate at 2 meters equals 25 mR/hr.
Exposure Rates VS. Distance - 100 mci Sources
||mR/hr @ 3'
||mR/hr @ 6'
||mR/hr @ 9'
Atomic particle, atom or chemical radical bearing an electrical charge,
either positive or negative. Ionization: The process by which a neutral
atom or molecule acquires a positive or negative charge.
Any electromagnetic or particulate radiation capable of producing ions,
directly or indirectly, in its passage through matter.
A neutron is an elementary nuclear particle with a mass slightly larger
than a proton and a net charge of zero.
Photons are much more penetrating than alpha and beta particles. X and
gamma radiation is never completely absorbed; however, we can choose a
shield composition and thickness which will reduce the intensity to non-hazardous
levels (see also: Half-value Layer). Generally,
high density materials are best suited for gamma shielding.
Radiation cannot be detected with the unaided senses, an instrument must
be used to identify presence, type or intensity of radiation. All instruments
consist of a detector and a measuring apparatus (some substance that responds
to the radiation and a system to measure the extent of the response). Some
detection systems use the ionization produced in them, and other systems
depend upon excitation. Chemical and photographic detection principles
are also used.
The property possessed by some elements (e.g.: uranium) of spontaneously
Rays by disintegration of the nuclei of the atoms. An element is said
to be radioactive if it can spontaneously decay or be transformed into
another element. This transformation is always accompanied by emission
of nuclear radiation.
Record of radiation from radioactive material in an object, made by placing
the object in close proximity to a photographic emulsion.
Isotopes are species of atoms of a chemical element with the same number
of protons but differing in the number of neutrons, resulting in the same
atomic number but different atomic masses. Some isotopes are unstable,
releasing energy in the form of radioactivity,
they are called radioisotopes.
The basic unit of exposure to X or gamma
radiation. The special unit of exposure. One R = 2.58 x 10-4
coulombs/kgm. of air. One milliroentgen (mR) is equivalent to 1/1000 of
See Dose Equivalent (Roentgen's Equivalent
The scintillation detector is composed of a sodium iodine crystal and a
photo multiplier that are usually glass encased. Every time a gamma ray
passes through the crystal, a small flash of light is emitted. The photo
multiplier picks up this flash and magnifies it to be registered as one
count. This makes for a very sensitive detector. For all practical purposes
there is no down time like that found in the Geiger - Mueller
Another advantage of the scintillation detector is that it can differentiate
energy levels in the counts. Thus it can be calibrated for use in spectrum
On the down side, scintillation detectors are expensive as compared
to Geiger - Mueller's and they are not very rugged.
Shielding is a method of radiation protection. A shield is a body of material
positioned to prevent or reduce the passage of radiation. The effectiveness
of a shield is determined by the interaction between the incident radiation
and the absorbing medium. See Half-value Layer.
A photon emanating from outside the nucleus of an
atom. It is not a particle but a form of very short wave electromagnetic
radiation, similar to gamma rays but originating outside the nucleus.
Penetrating electromagnetic radiation whose wave lengths are shorter
than those of visible light. They are usually produced by bombarding a
target (metallic) with fast electrons in a high vacuum. In nuclear reactions,
it is customary to refer to photons originating in the nucleus as Gamma
Rays and those originating in the extranuclear parts of the atom as X-rays.
They are sometimes referred to as Roentgen rays after Wilhelm Conrad Roentgen,
the discoverer. The only difference between X and gamma radiation is the
See Dose Equivalent (Roentgen's Equivalent