beam

beam,

n a stream or approximately unidirectional emission of electromagnetic radiation or particles.

beam, central,

n the center of the beam of roentgen rays emitted from the tube.

beam, useful,

n the part of the primary radiation that passes through the aperture, cone, or other collimator.

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beam

a unidirectional emission of electromagnetic radiation. See also x-ray.

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external beam therapy

radiotherapy in which the source is at a distance from the patient, e.g. orthovoltage, cesium-137, cobalt-60 or linear accelerator.

beam limitation

restriction of the divergent beam as it appears from the tube window by a lead plate or cone or a light beam diaphragm located at the window.

primary beam

the radiation beam as it passes through the window of the x-ray tube and before it is modified by extra-tube devices.