Fluke Biomedical TNT 12000 - Manual (Page 105)

Model 96035B Ion Chamber
Calibration and Verification
B
B-3
Average Intensity (mGy/s)
Average Intensity (R/min)
Collection Ef
ficiency
0.146
1 10 100 1000 10000
110%
100%
90%
80%
70%
60%
1.46 14.6 146 1460
Continuous
Half Wave
fct30.eps
Figure B-2. Collection Efficiency of Model 96035C Ion Chamber
Ion Transit Time .................................................... Maximum of 0.67 ms in the center of the chamber at STP with a bias
voltage of 300 volts.
Air Density Correction.......................................... To perform air density corrections when using a calibration factor with
a reference temperature of 22 ° C, multiply the ion current by the
following correction factor, F:
F = (273.15 + T) / (295.15 x P)
Where T is the temperature in ° C and P is the pressure expressed as
a fraction of a standard atmosphere (1013 hPa). For chambers with a
calibration factor normalized to 20
° C, the denominator is 293.15 x P.
Calibration and Verification
Calibration or calibration verification is performed by comparison of each 96035B ion
chamber with a reference chamber calibrated at either the National Institute of Standards
and Technology (NIST) or PTB.
Specifications for all PTB equivalent beam qualities are given in the tables in the energy
correction factor section.
Standard Calibration
The standard calibration is performed at one diagnostic and one mammographic beam
quality as given below. Calibration factors are normalized to 22 ° C and 1013 hPa of
atmospheric pressure.
Diagnostic Unattenuated beam: Calibration is performed at the Fluke Biomedical,
Radiation
Management Services equivalent of L100 (NIST defined as 100 kVp, first HVL of
2.8 mm Al, homogeneity coefficient of 59).
Mammographic beam: Calibration is performed at the Fluke Biomedical, Radiation
Management Services equivalent of MoMo28 (NIST defined as 28 kVp, first HVL of
0.332 mm Al, homogeneity coefficient of 74.3).
European Calibration Option
This calibration option replaces the standard calibration for units sold in Europe, or when
specifically requested by a customer. This option includes one diagnostic and one
mammographic beam quality, as given below. Calibration factors are normalized to
20 ° C and 1013 hPa of atmospheric pressure.