Maxray Cocoon - Bremsstrahlung Radiation; Characteristic Radiation; Primary and Scatter Radiation

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Cocoon Training Manual
Background
Generally, the three parameters that are usually adjusted by the X-ray technician (tube potential
(kVp), tube current (mA), and time (sec)) establish the characteristics of the X-ray beam emanating
from the tube. The tube potential determines the energy range of X rays and the tube current estab-
lishes the rate at which X rays are emitted. In the tube, X rays are produced by two means, Brems-
strahlung radiation and characteristic radiation. The two are described below.
Bremsstrahlung Radiation
This is the main type of radiation produced and occurs as the high energy electrons experience a
sudden slowing down, or “breaking”, at the anode target. A spectrum of photon energies is produced.
Bremsstrahlung is also known as “breaking radiation”.
Characteristic Radiation
This type of radiation is produced when an electron interacts with an inner shell electron of a target
atom of the anode. As the inner shell electron is displaced, an electron from an outer shell drops to
fill the vacancy. It is this process that releases characteristic X rays.
All X-ray tubes have some form of filtration, whether it be inherent to the design or added afterward
to adjust the usefulness of the X-ray beam. The X-ray housing will have additional shielding to mini-
mize “leakage radiation” that can cause unwanted exposure to the technician.
Primary and Scatter Radiation
Once X rays leave the tube housing, they are categorized as primary or secondary radiation. Second-
ary radiation is further characterized into scatter radiation and leakage radiation.
Primary radiation
This type of radiation describes the useful beam of radiation that is produced in the tube and exits the
filtration window as designed. This is the radiation which is fundamental in producing the radiograph.
Continued exposure to the primary beam can result in a significant hazard.
Scatter radiation
This refers to the radiation that is scattered after the primary beam interacts with the patient. The pa-
tient is therefore the major source of scatter radiation. Even though the primary beam is much more
intense than scatter radiation, it is this scatter that is of primary concern when protecting the safety
of the worker.
As stated above, leakage radiation refers to radiation from the X-ray tube that penetrates the device
housing. Leakage is usually quite small relative to the primary beam and scatter.
Interactions with Matter
The interaction of X rays with matter is a random process. As tissue is exposed, the X rays may inter-
act with the atoms of the material through which they pass. A small percentage of the X rays will pass
through matter without interacting.