Fluke Biomedical 440RF - Manual (Page 11)

Operation
Instrument Positioning and Scanning
2
2-3
the magnesium window, an operator should keep the window facing the field of increasing intensity (or
toward the source).
The instrument responds to the effective exposure rate or dose equivalent rate averaged throughout the
chamber volume. An exposure rate or dose equivalent rate 10 or 100 cm away cannot be predicted
without knowledge of the shape, direction, and contours of the radiation field involved. If this concept of
measuring a local field, rather than a general area, is remembered, confusion can be avoided.
Operator knowledge regarding the location of radiation sources can be divided into several classifications
which include precise location, general vicinity, and no specific location. Each classification requires a
specialized approach.
Precise Location
When positioning the instrument in a field where a nominal indication will occur, no position adjustments
are necessary. When placing the instrument in a field where maximum indication is desired, minor
position adjustments may be necessary.
General Vicinity
A small amount of careful scanning, less than a few square feet, can be employed so that a small
indication will be visible on the scale and so that fatigue will not occur. See Figure 2-2. Maximum scan
line speed should be between 2 and 4 feet/minute depending upon how low the source intensity
encountered.
The scanning motion should be slow, smooth, and uniform. If any upscale indication is encountered, the
scan should be stopped immediately in order to determine whether the instrument detected a cosmic ray
or a tiny intense beam.
Scanning should be performed with minimum
jostling or jarring of the instrument, particularly
when a low exposure rate or dose equivalent rate is
underway.
No Specific Location
Scanning of large areas at low exposure or dose equivalent rates is not recommended for this instrument.
NOTE