Calibrating the AEC February 5, 2004 4-5
Determining the Half Value Layer (HVL)
Select the Determine HVL procedure option if you need to determine the HVL of
the X-ray Generator for a given target/filter combination.
This procedure requires taking four exposures.
• The first exposure and the last exposure are “control” exposures with no
attenuating material in place.
• The second exposure is taken with Aluminum in the path of the X-ray beam.
For the Molybdenum target, use a 0.3-mm thickness of Aluminum. For the
Tungsten target, use a 0.4-mm thickness of Aluminum.
• The third exposure is taken with a thicker amount of Aluminum in the path of
the X-ray beam.
- For the Molybdenum target and Molybdenum filter, use a 0.4-mm
thickness of Aluminum.
- For the Molybdenum target and Rhodium filter, use 0.5-mm.
- For the Tungsten target and Rhodium filter, use a 0.6-mm thickness of
Aluminum.
The result of the HVL procedure is a fractional number representing the HVL in
millimeters of Aluminum.
NOTE: If you already know the HVL and want to proceed with determining the ESE value, go to
“Determining the Entrance Skin Exposure (ESE)” on page 4-8.
To determine the HVL value:
1. In the tool’s main window, select the Determine HVL procedure option.
In the main window, the settings change and instructional text is displayed:
• The HVL procedure has been selected
• The units have been changed to R/mR
• The default AGD is now displayed in mrad instead of mGy
• Instructions for Generator and dosimeter configuration are displayed in
the text window
An example of the main window with the Determine HVL procedure option
selected is shown below.
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