2. Description of the Barracuda
Hardware and Specifications
2012-10/4.3A
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Barracuda & QABrowser Reference Manual
Note: These values are typical values measured at PTB in Germany in 2009.
2.6.2.4 Angular Sensitivity, MPD
In this section you can see graphs of the typical angular sensitivity for dose measured
with the MPD at 28 and 70 kV. The setup is shown in figures below.
This "directional" behaviour makes it excellent for reproducible measurements, with
less influence by nearby spreading matter. This makes it possible to make accurate
HVL measurements even when measuring with "bad geometry", which is especially
interesting for mammography. To understand, please see the polar plot shown below.
The MPD is shown to the left, and a typical mammographic ion chamber to the right.
There are two different graphs, depending on the product version of your MPD. The
product version is the version number you can find on the label on the bottom of the
MPD. If the version of your MPD is 1.X, use the graphs marked v1. For 2.X and higher
use graphs marked v2.
For v1.X it is however important that you place the detector surface
perpendicular to the direction of the radiation source or that you make
corrections according to the tables in section Corrections for Angular
Sensitivity .
For radiography this is generally no problem, since most measurements are performed
in the middle of the field, perpendicular to the incident radiation.
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