2-2. COMMON RADIATION TERMS AND VALUES

SECTION III OPERATOR MAINTENANCE PROCEDURES

TM-5-6635-386-12P Density and Moisture Tester Manual
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TM 5-6635-386-12&P 2-2. COMMON RADIATION TERMS AND VALUES Radiation is similar to light. It increases in intensity by a factor of FOUR each time the distance from the source is cut in HALF. The radiation level drops by a factor of FOUR each time you move TWICE as far away from the source. Certain terms are used to describe radiation factors important to tester users. Be familiar with the following terms and values: CURIE: A term used to describe the size of a radioactive source. It represents a quantity of material disintegrating 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. MILLICURIE: One thousandth (1/1000) of a curie. MICROCURIE: One millionth (1/1, 000, 000) of a curie. ROENTGEN: A term describing the amount of radiation 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. REM (rem): This is a better term for measuring human exposure accumulation than Roentgen because it has been corrected to provide a common base for radiation effects on people. Some radiation is highly penetrating and would be more potentially dangerous than other forms. The descriptions become equal when they are all corrected to the common rem base. MILLIREM (mrem): One thousandth (1/1000) of a rem. Tester radiation levels are commonly measured in these very small units. MILLIREM/HOUR (mrem/hr): A term used to describe the "brightness" of a radioactive gamma source. It is the strength of the radiation field at the point of measurement. This term is similar to footcandles of light when discussing light. The brightness of the radiation field will be dictated by the type of radioactive material involved, the size of the source, the amount of shielding present, and the distance from the source. The total amount of radiation accumulated would then become a factor of how much time was spent in the radiation field. NOTE Since the tester uses small, well shielded sources, operators will be involved with only millirems of radiation and with levels which are only in the mrem/hr range. 100 mrem: Weekly allowed dose (5 rem/yr is max annual work dose). 5 mrem/hr: Average radiation dose at tester surface. 1/2 mrem/hr: Average gamma dose at 2’ from tester (arm’s length). 1/3 mrem/hr: Average neutron dose at 3’ from tester (source to midtrunk distance when carrying tester). 1/2 mrem: Average heavy workweek accumulation of radiation for a tester user (1/200th of allowed dose). 2-2

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