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ITG SUBJECT: RADIATION PROTECTION TERMINOLOGY
The recent incident at the Soviet Union's Chernobyl nuclear power plant
has heightened concerns for radioactive contamination in FDA regulated
products. The potential hazard will undoubtedly necessitate increased sampling
of both imported and domestic food products such as produce, milk, etc.
A list of technical terms has been compiled to serve as a quick reference
for the terminology associated with radiation protection. If you have any
concerns and questions on radiation protection, contact the Regional Radiological
Health Representatives (RRHR).
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| alpha particle ( ) |
A charged particle emitted from the nucleus
of an atom having a mass and charge equal
in magnitude to a helium nucleus. It cannot
penetrate the outer layer of the skin and
represents very little external hazard. |
| becquerel (Bq) | A unit of measurement of activity. See the
Conversion Table.
|
| beta particle (ß) | A charged particle emitted from the nucleus
of an atom, with a mass and charge equal in
magnitude to that of the electron. It has a
penetrating range of a few feet in air and
can be easily stopped by a thin sheet of
metal or plastic.
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| counter | Geiger-Muller (G-M) counter
A radiation detection and measuring
instrument consisting of a gas-filled tube
and associated electronic circuits.
Scintillation counter
A radiation measuring instrument consisting
of phosphor, photomultiplier tube, and
associated electronic circuits for counting
light emissions produced in the phosphor by
ionizing radiation. It is a more sensitive
device than the G-M counter.
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| curie (Ci) | The special unit of activity. One curie equals 3.7 x 10 10 nuclear transformations
per second. This unit reflects the
intensity of the radioactive source.
Some common fractions are:
Millicurie: One thousandth (10 -3) of a
curie (mCi)
Microcurie: One millionth (10 -6) of a
curie (µCi)
Nanocurie: One billionth (10 -9) of a
curie (nCi)
Picocurie: One millionth of a microcurie
(10 -12) (pCi) |
| dose, absorbed | The energy imparted to matter by ionizing radiation per unit mass of irradiated
material. The unit of absorbed dose is the
rad.
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| dose equivalent (DE) | The quantity that expresses all radiation
on a common scale for calculating the
effective absorbed dose. It is defined as
the product of the absorbed dose in rads
and certain modifying factors. The unit of
DE is the rem.
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| dosimeter | A portable instrument for measuring and
registering total accumulated gamma ray
exposure. Two common types are the
"self-reading" pocket size dosimeters and
the TLD (thermal luminescent dosimeter)
requiring laboratory processing. Dosimeter
readings are normally in roentgens or
milliroentgens.
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| exposure | A measure of the ionization produced in the
air by X or gamma radiation. The special
unit of exposure is the roentgen.
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| gamma ray ( ) | High-energy, short wavelength
electromagnetic radiation, emitted from the
nucleus. Gamma rays are similar to X-rays,
but are usually more energetic. It travels
at the speed of light and is the most
penetrating type of radiation.
gray (Gy) A unit of absorbed dose. See the
Conversion Table.
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| half-life, radioactive | Time required for a radioactive substance to lose 50% of its activity by decay. Each
radionuclide has a unique half-life.
| Radionuclide | Half-life (approximate)
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| barium (Ba) 140 | 13 days |
| cesium (Ce) 134 | 2 years |
| cesium (Ce) 137 | 30 years |
| cobalt (Co) 60 | 5 years |
| iodine (I) 131 | 8 days |
| strontium (Sr) 90 | 30 years |
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| Protective Action Guides Refer to Federal Register, Oct. 22, 1982.
for human food (FDA) |
rad (radiation
absorbed dose) | The unit of absorbed dose equal to 100 ergs per gram or 0.01 joule per kg.
|
| radiation, background | Radiation arising from radioactive material
in the environment. Background radiation
due to cosmic rays and naturalr
adioactivity is always present. The
estimated total dose a person receives from
natural radiation in the U.S. is 100
mrem/year.
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| radiation, external | Radiation from a source outside the body.
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| radiation, internal | Radiation from a source within the body (as
a result of the deposition of
radionuclides in body tissue).
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| radiation, ionizing | Any electromagnetic or particulate
radiation capable of producing ions,
directly or indirectly, in its passage
through matter.
|
relative biological
effectiveness | The RBE is a factor used to compare the (RBE) biological effectiveness of absorbed
Radiation doses (i.e., rads) due to
different types of ionizing radiation. The
RBE is the ratio of rem to rad.
|
rem (roentgen
equivalent man) | A special unit of dose equivalent. The dose
equivalent in rems is numerically equal to
the absorbed dose in rads multiplied by
certain modifying factors. With X or gamma
rays, the factor is close to one, so I rem
is equal to 1 rad.
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| roentgen (R) | The special unit of exposure. One roentgen
equals 2.58 x 10 -4 coulomb per Kg. of
air.
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| sievert (Sv) | A unit of dose equivalent. See the
Conversion Table.
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| X-rays | Penetrating electromagnetic radiation whose
wave lengths are shorter than those of
visible light. In nuclear reactions, it is
customary to refer to photons originating
in a nucleus as gamma rays, and those
originating in the extranuclear part of the
atom as X-rays. These rays are sometimes
called roentgen rays, after their
discoverer, W. K. Roentgen.
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CONVERSION TABLE
| quantity |
international
unit & symbol
used in Europe
and Canada |
int'l system units |
old special
unit & symbol
factor
used in U.S. |
conversion |
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| activity |
becquerel
(Bq) |
s -1 |
curie (Ci) |
1 Bq ?? 27 pCi |
| exposure |
- |
CKg -1 |
roentgen (R) |
1 Ckg -1 ?? 3876 R |
absorbed
dose |
gray (Gy) |
Jkg -1 |
rad (rad) |
1 Gy = 100 rad |
dose
equivalent |
sievert
(Sv) |
Jkg -1 |
rem (rem) |
1 Sv = 100 rem |
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Acknowledgment
We wish to acknowledge gratefully the technical information provided
by Dr. Donald L. Thompson and Mr. Gail D. Schmidt, Office of Health Physics.
References
The Effects on Populations of Exposure to Low Levels of Ionizing Radiation:
1980, Committee on the Biological Effects of Ionizing Radiations, Division
of Medical Sciences, Assembly of Life Sciences, National Research Council,
National Academy Press, Washington, D.C., 1980.
Glossary of Terms: Nuclear Power and Radiation, U.S. Nuclear Regulatory
Commission, Washington, D.C. 20555, June 1981.
Handbook of Forensic Science, FBI, March 1984.
Federal Register, Vol. 47,47073-83. Oct. 22, 1982.
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