Fluke Biomedical TNT 12000 - Manual (Page 109)

Model 96035B Ion Chamber
Calibration and Verification
B
B-7
Figure C-5. DH70 is a new PTB beam quality with an HVL of 6.77, which falls between
DN70 and DN80. Since the response of the chamber at H60 is virtually identical to the
response at DN70, this curve is also considered normalized to H60.
Users receiving the standard calibration must request a calibration factor at either H60 or
DH70 to use the correction factors in this curve.
All 96035B ion chambers must have an actual correction factor within
± 1.5 % of the
value shown in the curve at any point. 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 measurements in an attenuated beam not similar
to a DN series point, the user may measure the actual first HVL and locate the proper
correction value on the curve. See Figure B-5.
Typical Correction Factors - Diagnostic Attenuated Beam
Normalized to H60 and DH70
First HVL (mm A1)
Colrrection Factor
2 3 4 5 6 7 8 9 10 11 12 13 14 15
1.08
1.06
1.04
1.02
1
0.98
0.96
0.94
0.92
150 120
100 90
80
50
40
60
70
fct37.eps
Figure B-5. Energy Correction Factors for Model 96020C in Attenuated Beam
Mammographic Beam Qualities
The energy correction factors for the 96035B are determined for the mammographic
beam using the PTB defined MV and MH series of beam qualities given in Table B-3 and
Table B-4, respectively.
Table B-3. Specifications fo PTB Defined Unattenudated Mammographic Beam Qualities
PTB Denomination kVp Added Filtration First HVL in mm AI
MV20 20 30 μ m Mo 0.223
MV25 25 30 μ m Mo 0.282
MV30 30 30 μ m Mo 0.337
MV35 35 30 μ m Mo 0.374
MV40 40 30 μ m Mo 0.402
MV50 50 30 μ m Mo 0.440