Fluke Biomedical 440RF - Manual (Page 20)

Victoreen 440RF/D
Operators Manual
2-12
Figure 2-8. Plane Source (Color TV Screen)
2.7 Chamber Corrections
Energy Dependence
The definition of exposure rate (refer to Unit of Measurement) did not reference any specific photon
energy. Any ion chamber has a certain energy dependence. If the exposure rate is held constant, the
chamber will respond differently to slightly different energy photons. The Model 440RF/D has been
calibrated at an effective energy of 21 keV. The response is fairly independent in the low-energy region.
For accurate usage at middle and high-energy regions, the energy response correction curve shown in
Figure 2-9 must be used.
For example, a monochromatic source of X-ray known to have an effective energy of 100 keV indicates
42 mR/h on the instrument. Figure 2-9 indicates that a correction factor of about 0.67 is required. This
will convert the reading to 28.1 mR/h.
Ion
Chamber
5 cm
Magnesium Window
Bumpe
Steel Shadow-Mask (Major Photon Source)
Phosphor Screen
Glass Face Plate
Model 440RF/D
Probe Assembly
Case