MILLIREM (mrem): One thousandth (1/1000) of a rem.

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.

at the rate of 3.7 x 10 disintegrations per second, or the

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

work dose).

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

(arm's length).

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).

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