Fluke Biomedical TNT 12000 User Manual

Page 107

Model 96035B Ion Chamber

Calibration and Verification

B-5

Table B-1. Specifications for PTB Defined Unattenuated Beam Qualities

PTB

Denomination

kVp

Added Filtration

in mm AI

First HVL in mm

DN30 30

2.5 1.05

0.031

DN40 40

2.5 1.42

0.045

DN50 50

2.5 1.82

0.059

DN70 70

2.5 2.45

0.081

DN90 90

2.5 3.10

0.112

DN100 100

2.5 3.60

0.126

DN120 120

2.5 4.30

0.165

DN150 150

2.5 5.40

0.231

DN30 30

2.5 1.05

0.031

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. L100 is chosen as the reference point for chambers receiving the

standard calibration while DV70 is chosen for chambers receiving the PTB calibration

option.
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 typical correction factor curves for the unattenuated beam are shown below

normalized to L100 in Figure B-3 and DV70 in Figure B-4.

Typical Correction Factors - Diagnostic Unattenuated Beam

Normalized to L100

First HVL (mm A1)

Colrrection Factor

1.5

2.5

3.5

4.5

5.5

1.08

1.06

1.04

1.02

0.98

0.96

0.94

0.92

120

150

100

fct39.eps

Figure B-3. Energy Correction Factors for Model 96035C in Unattenuated Beam Normalized to L100