EFFECTIVE DOSE EQUIVALENT	The sum of the products of the dose equivalent to the organ or tissue and the weighting factors applicable to each of the body organs or tissues that are irradiated.
EFFICIENCY	A measure of the probability that a count will be recorded when radiation is incident on a detector. Usage varies considerably so be aware of which factors (window, transmission, sensitive volume, energy dependence, etc.) are included in a given case. At Wayne State University, we are referring to the percent of total activity present for a given radionuclide detected by the radiation detection instrument being used.
ELECTROMAGNETIC	A traveling wave motion resulting from changing electric or magnetic fields. Familiar electromagnetic radiations range from x-rays and gamma rays of short wavwelength, through the ultraviolet, visible, and infrared regions, to radar and radio waves of relatively long wavelength. All electromagnetic radiations travel in a vacuum wth the speed of light.
ELECTRON	A negatively charged elementary particle which is a constituent of every neutral atom. Its unit of negative electricity equals 4.8 E-19 coulombs. Its mass is 0.000549 atomic mass units (amu).
ELECTRON CAPTURE	A mode of radioactive decay involving the capture of an orbital electron by its nucleus. Capture from the particular electron shell is designated as "K-electron capture","L-electron capture", etc.
ELECTRON VOLT	A unit of energy equivalent to the amount of energy gained by an electron in passing through a potential difference of 1 volt, abbreviated (ev).
EPIDERMIS	The outermost layer of cells of the skin.
EPILATION	The temporary or permanent removal or loss of hair.
ERG	The unit of energy or work in the centimeter-gram-second system; the work performed by a force acting over a distance of one centimeter to result in a one gram mass being accelerated at a rate of one centimeter per second, each second.
ERYTHEMA	An abnormal redness of the skin due to distension of the capillaries with blood.
EXPOSURE	Being exposed to ionizing radiation or radioactive material. A measure of the ionization produced in air by x or gamma radiation. It is the sum of the electrical charges on all ions of one sign produced in air when all electrons liberated by photons in a volume element of air are completely stopped in air, divided by the mass of air in the volume element. The special unit of exposure is the Roentgen.
EXTERNAL DOSE	That portion of the dose equivalent received from radiation sources outside the body.
EXTREMITY	Hand, elbow, arm below the elbow, foot, knee, or leg below the knee.
EYE DOSE EQUIVALENT	Applies to the external exposure of the lens of the eye and is taken as the dose equivalent at a tissue depth of 0.3 centimeters (300 mg/cm squared).