RADIATION EXPOSURE AND UNITS

RADIATION EXPOSURE AND UNITS

The (traditional/conventional) radiation units of measurement, the

roentgen, rad, and rem, are of importance to the radiographer—the SI (Standard International) units of measure are gaining in usage and should also be used by the radiographer

The roentgen is a unit of measurement of ionization in air, and referred to as the unit of exposure. Because x-rays ionize air, all the ions of either sign (positive or negative) formed in a particular quantity of air are counted and equated to a quantity of radiation expressed in the unit roentgen. The roentgen is valid only for x and gamma radiations at energies up to3 MeV (million electron volts). The roentgen SI unit of measurement is C/kg (coulomb per kilogram).

THE RAD

The rad is an acronym for radiation absorbed dose. As radiation passes through matter, a certain amount of energy is deposited in that matter. Absorbed dose refers to the amount of energy deposited per unit mass and is strongly related to chemical change and biologic damage. The amount of energy deposited and, thus, the amount of possible biologic damage is dependent on the following:

• Type of radiation

• Atomic number of the tissue

• Energy of the radiation

The rad SI unit of measurement is the Gy (gray).

THE REM

The rem is an acronym for radiation equivalent man. The rem uses the information collected for the rad, but also uses a quality factor (QF) to predict biologic effects from different types of radiation. Thus, the equation: rad × QF = rem. Radiations having a high QF have a higher LET and greater potential to produce biologic damage. The rem is described as the unit of dose equivalency (DE) and used to express occupational exposure.

The rem SI unit of measurement is the Sv (sievert).

Personal Radiation Monitors:

• OSL

• TLD

• Film Badge

• Pocket Dosimeter

SUMMARY

The roentgen (R unit), or unit of exposure, is the unit used to

describe quantity of ionization in air.

The rad describes absorbed dose.

The rem is the unit of dose equivalency (DE), used to quantify biological effectiveness.

The OSL is the newest, most accurate personal dosimeter. It

uses a thin layer of Al2O3 to store information.

Film badges are convenient, low-cost radiation monitors that

are processed monthly.TLDs use LiF crystals to store exposure information. They are more precise and more expensive than film badges and may be processed quarterly.

Film badges and TLDs measure exposure to beta, x, and

gamma radiation.

Pocket dosimeters are thimble ionization chambers used to

monitor larger quantities of radiation exposure, up to 200

mR.

Radiographers must strive to keep their occupational dose

ALARA.