MILLIREM (mrem): One thousandth (1/1000) of a rem.
2-2. COMMON RADIATION TERMS AND VALUES
Tester radiation levels are commonly measured in these
very small units.
Radiation is similar to light. It increases in intensity by a
factor of FOUR each time the distance from the source
MILLIREM/HOUR (mrem/hr): A term used to describe
is cut in HALF.
the "brightness" of a radioactive gamma source. It is the
strength of the radiation field at the point of
The radiation level drops by a factor of FOUR each time
measurement. This term is similar to footcandles of light
you move TWICE as far away from the source.
when discussing light.
Certain terms are used to describe radiation factors
The brightness of the radiation field will be dictated by
important to tester users. Be familiar with the following
the type of radioactive material involved, the size of the
terms and values:
source, the amount of shielding present, and the
distance from the source. The total amount of radiation
CURIE: A term used to describe the size of a radioactive
accumulated would then become a factor of how much
source. It represents a quantity of material disintegrating
time was spent in the radiation field.
same rate as one gram of Radium. This is not an index
of how dangerous the source might be, but only an index
of quantity of the material in question.
Since the tester uses small, well shielded
MILLICURIE: One thousandth (1/1000) of a curie.
sources, operators will be involved with only
millirems of radiation and with levels which are
MICROCURIE: One millionth (1/1, 000, 000) of a curie.
only in the mrem/hr range.
ROENTGEN: A term describing the amount of radiation
100 mrem: Weekly allowed dose (5 rem/yr is max annual
accumulated or exposed to, by standing near a large
radioactive, unshielded source for a short time or near a
small, unshielded source for a long time.
5 mrem/hr: Average radiation dose at tester surface.
REM (rem): This is a better term for measuring human
1/2 mrem/hr: Average gamma dose at 2' from tester
exposure accumulation than Roentgen because it has
been corrected to provide a common base for radiation
effects on people. Some radiation is highly penetrating
1/3 mrem/hr: Average neutron dose at 3' from tester
and would be more potentially dangerous than other
(source to midtrunk distance when carrying tester).
forms. The descriptions become equal when they are all
corrected to the common rem base.
1/2 mrem: Average heavy workweek accumulation of
radiation for a tester user (1/200th of allowed dose).