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8. Glossary
Piranha & QABrowser Reference Manual 2014-06/5.5C
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8 Glossary
Absorbed dose (D)
The energy imparted per unit mass by ionizing radiation to matter at a specified point.
The SI unit of absorbed dose is joule per kilogram (J/kg). The special name for this unit
is gray (Gy). The previously used special unit of absorbed dose was the rad. 1 rad =
0.01 Gy. 1 Gy = 100 rad. (See Report No. 82, NCRP, 1985b.)
SI unit: Gy = J/kg
Absorbed dose rate (D')
absorbed dose per unit time. Absorbed dose rate is determined as the quotient of dD by
dt, where dD is the increment of absorbed dose in the time interval dt: D'=dD/dt. A unit
of absorbed dose rate is any quotient of the gray or its multiples or submultiples by a
suitable unit of time (Gy/s, mGy/h, etc.).
SI unit: Gy/s = J/kg·s
Absorption, energy
Phenomenon in which incident radiation transfers to the matter which it traverses some
or all of its energy.
Activity
The number of nuclear transitions occurring in a given quantity of radioactive material
per unit time. The SI unit of activity is s
-1
. The special name for the unit of activity is
becquerel (Bq). The previously used special unit of activity was the curie (Ci). 1 Bq = 2.7
x 10
10
Ci. 1 Ci = 3.7 x 10
10
Bq. (See Report No. 82, NCRP, 1985b.)
SI unit: Bq = s
-1
Additional filtration
ADDED FILTERS and other removable materials in the RADIATION BEAM which are
between the RADIATION SOURCE and the PATIENT or a specified plane.
See also filter.
Air kerma
See kerma.
Aluminium equivalent or Aluminium Attenuation Equivalent (AAE)
The thickness of aluminum affording the same attenuation, under specified conditions,
as the material in question.
Anode
In a X-ray tube, electrode to which electrons forming a beam are accelerated and which
usually contains the target.
Aperture
(e.g., for computed tomography) - the opening in the collimation that allows radiation to
reach the detector.
Area exposure product
Product of the area of a cross-section of a radiation beam and the averaged exposure
over that cross-section.
SI unit: Gy·m²
Attenuation
The reduction of radiation intensity upon passage of radiation through matter.