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|  Radiological Assessor Training
DOE-HDBK-1141-2001
Student's Guide
III. X-ray machines
A. Components
X-ray devices have been in existence for about
100 years. Although there are many different
designs of x-ray machines, they all have the
same basic components. These include a
source of electrons, an electrical potential
difference to accelerate the electrons, and an
anode, or target for the accelerated electrons to
strike.
Usually, the source of electrons in an x-ray
machine is a thin wire filament from which
electrons are emitted when it is heated by a
large electrical current. Controlling the current
through the filament, then, becomes a way to
control the number of electrons available for
The electrical potential difference between the
cathode (filament) and the anode (or target) is
the force that accelerates the electrons. The
larger the potential difference, the more kinetic
energy the electrons will acquire. The potential
difference is measured in units of kilovolts (kV).
The energy of the electrons is measured in units
of kilo electron volts (keV), with one electron volt
being the amount of energy required to move
one electron through a potential difference of
one volt.
The accelerated electrons then strike the anode
(or target). The target may consist of various
materials, depending on the purpose and design
of the x-ray tube. X-ray production is most
efficient in high atomic number targets, like
tungsten.
Module 12 - 2
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