DOSE RATE

a. Up to now, we have discussed dose as a total quantity. A dose of radiation is an expression of how much. A particular dose might be the result of a year’s exposure or a day’s exposure to radiation.

b. This brings us to another term to consider--dose rate. The dose rate tells us how fast or slow radiation is being delivered. Dose rate is to dose as miles per hour is to total miles driven.

c. The dose rate is expressed as dose per unit of time, i.e., rads/hour, roentgens/sec, etc.

d. Total dose is obtained by multiplying the dose rate by the time of exposure where the dose rate remains constant.

Dose = Dose Rate x Time

UNIT: Roentgen
SYMBOL: R
DEFINITION: The quantity of x or gamma radiation that will produce, in 0.001293 grams (1 cc) of standard air, ions carrying one electrostatic unit (esu) of charge of either sign.

UNIT: Radiation Absorbed Dose
SYMBOL: rad
DEFINITION: The quantity of ionizing radiation of any type that results in the absorption of 100 ergs per gram in any material.

UNIT:Roentgen Equivalent Man
SYMBOL: rem
DEFINITION: The quantity of ionizing radiation of any type which, when absorbed by man, produces a physiological effect equivalent to that produced by the absorption of one roentgen of x or gamma radiation.