Fluke Biomedical TNT 12000 - Manual (Page 99)

Model 96020C Ion Chamber
Calibration and Verification
A
A-5
Typical energy correction factor curves are obtained by dividing the calibration factor at
each beam quality by the calibration factor at a reference point and plotting the result
versus first HVL. The first HVL at H60 is chosen as the reference point for chambers
receiving the standard calibration while the first HVL at DH70 is chosen for chambers
receiving the PTB calibration option. DH70 is a new calibration point defined by PTB
with a first HVL of 6.77, which falls between DN70 and DN80 in the table above. The
correction factor charts normalized to these two points are shown in Figure A-3 and
Figure A-4.
Typical Correction Factors - Attenuated Beam
Normalized to H60
First HVL (mm A1)
Colrrection Factor
2 3 4 5 6 7 8 9 10 11 12 13 14 15
1.05
1.04
1.03
1.02
1.01
1
0.99
0.98
0.97
0.96
0.95
150 120 100
90 80
50
40
60
70
fct31.eps
Figure A-3. Energy Correction Factors for Model 96020C in Attenuated Beam Normalized to H60
Typical Correction Factors - Attenuated Beam
Normalized to DH70
First HVL (mm A1)
Colrrection Factor
2 3 4 5 6 7 8 9 10 11 12 13 14 15
1.05
1.04
1.03
1.02
1.01
1
0.99
0.98
0.97
0.96
0.95
150
90
50
40
60
70
120
80
100
fct34.eps
Figure A-4. Energy Correction Factors for Model 96020C in Attenuated Beam Normalized to DH70
All 96020C ion chambers must have an actual correction factor within ± 1.5 % of the
value shown in the curves at any point.
The energy correction factors are multiplicative, such that multiplying the measured ion
chamber output at any beam quality by the appropriate value from the curve will correct
readings not made at the calibration factor beam quality.
The numerical value shown beside each point is the kVp value of that point in the DN
series of beam qualities. Users making measurements in an attenuated beam with
characteristics similar to the PTB DN series may use these values to easily obtain the
appropriate correction factor. For a more precise correction factor value, or when making