Fluke Biomedical 10100AT - Manual (Page 25)

Operation
Basic Measurement Techniques
2
2-7
Important implications of the 0.25 pA threshold for exposure rate measurements and the 0.5 pC threshold
for integrated exposure measurements in the case of integral exposure are the minimum radiological
quantities that can be measured.
Table 2-1. Threshold Minimum Roentgen readings
Ion Chamber Measurement Units Minimum Reading
15 cc R/s 60
μ
R/min 3.6 m
R/hr .22
R/frame 1
μ
R 60
μ
150 cc R/s 6
μ
R/min .36 m
R/hr 22 m
R/frame 0.1
μ
R 6
μ
To find minimum readings in other radiological units, use the following multipliers of the roentgen factors:
0.000258 for Coulombs/kg air
0.00876 for Grays (in air)
0.01 for Sieverts (in air)
Ion Chamber Selection
The primary purpose of the Model 35050AT Dosimeter is to measure the ionizing radiation outputs of
typical diagnostic x-ray machines. This will likely be done with either of the two ion chambers standard in
the Model 10100AT TRIAD Field Service Kit: Model 96020C Ion Chamber, 150 cc or Model 96035B Ion
Chamber, 15 cc. Typical units of use will be exposure, exposure rate or exposure per frame.
The choice of which ion chamber to use will depend upon the sensitivity required, the beam size, beam
accessing port dimensions or the performance of a special function (e.g. CT probe).
Once a suitable ion chamber is selected, it is interconnected with the Model 35050AT Dosimeter by
means of the 6.1 m (20 ft) low-noise triaxial cable supplied and stably positioned at the measurement
point of interest by means of the test stand (see section 2.9) or ion chamber cable stem (see section
2.10) or other means. The dosimeter may be located where convenient and where both the dosimeter
and the operator are out of the radiation field. The dosimeter may now be turned on.
Verify Ion Chamber Selection
After the opening screen sequence, the instrument will go to the DETECTOR SELECT screen and await
a key press. If the ion chamber in use is not displayed, press the UP or DOWN buttons until it is.
Make sure that air density correction or no air density correction is what is desired--or required by the
nature of the detector, e.g., sealed chamber. If air density corrections are desired see section 2.2.1 and
2.11.2.
If very low dose rate measurements are desired, find an ion chamber with VLDR in its description. This
option should only be used with ion chambers suitable for very low dose rate measurements
Automatic Temperature & Pressure Sensing
The Model 35050AT Dosimeter contains an integrated temperature/pressure sensor. When using the
automatic temperature and pressure sensing feature, the measured temperature is the internal