Farmer Chamber
Model/Serial: 30010-002591 (purchased: 2014)
Model/Serial: 30010-002592 (purchased: 2014)
Description: Verified ionization chamber (0.6 cm3) for absolute dosimetry. We use this non-waterproof chamber with Unidos or Unidoswebline in the home-made gantry-mounted PMMA phantom to check linac dose output during weekly linac QA.
Calibration History: Farmer 2591 + Unidos 10396
| Date |
NW |
U |
ppol (60Co) |
ps (60Co) |
NW' [Gy/C] |
Laboratory |
| 25.04.2016 |
1.009 |
0.014 |
|
|
5.371E+07 |
Seibersdorf |
| 21.06.2018 |
1.010 |
0.014 |
|
|
5.371E+07 |
Seibersdorf |
| 14.09.2020 |
1.008 |
0.014 |
|
|
5.371E+07 |
Seibersdorf |
| 21.06.2022 |
1.011 |
0.014 |
|
|
5.371E+07 |
Seibersdorf |
| 19.06.2024 |
1.009 |
0.014 |
|
|
5.371E+07 |
Seibersdorf |
Calibration History: Farmer 2591 + Unidoswebline
| Date |
NW |
U |
ppol (60Co) |
ps (60Co) |
NW' [Gy/C] |
Laboratory |
| 25.04.2016 |
1.010 |
0.014 |
1.000 |
1.000 |
5.371E+07 |
Seibersdorf |
| 21.06.2018 |
1.010 |
0.014 |
1.000 |
1.000 |
5.371E+07 |
Seibersdorf |
| 14.09.2020 |
1.009 |
0.014 |
1.000 |
1.000 |
5.371E+07 |
Seibersdorf |
| 21.06.2022 |
1.011 |
0.014 |
1.000 |
1.000 |
5.371E+07 |
Seibersdorf |
| 19.06.2024 |
1.008 |
0.014 |
1.000 |
1.000 |
5.371E+07 |
Seibersdorf |
| 18.06.2026 |
1.009 |
0.014 |
|
|
5.371E+07 |
Seibersdorf |
Calibration History: Farmer 2592 + Unidos 10398
| Date |
NW |
U |
ppol (60Co) |
ps (60Co) |
NW' [Gy/C] |
Laboratory |
| 30.05.2015 |
1.007 |
0.014 |
1.000 |
1.000 |
5.371E+07 |
Seibersdorf |
| 13.06.2017 |
1.011 |
0.014 |
1.001 |
1.000 |
5.371E+07 |
Seibersdorf |
| 19.11.2019 |
1.011 |
0.014 |
1.001 |
1.000 |
5.371E+07 |
Seibersdorf |
| 22.06.2021 |
1.011 |
0.014 |
1.001 |
1.000 |
5.371E+07 |
Seibersdorf |
| 19.06.2023 |
1.012 |
0.014 |
1.001 |
1.000 |
5.371E+07 |
Seibersdorf |
| 18.06.2025 |
1.013 |
0.014 |
1.001 |
1.000 |
5.371E+07 |
Seibersdorf |
Notes
- U = k uc is the expanded uncertainty with the coverage factor k = 2.
- The first calibration of the chamber was performed in Germany (PTW). Immediately after purchase, the chamber was verified and once more calibrated in Austria. The apparent "jump" in the 60-Co calibration factor Nw can be partly attributed to the different positioning rules in the two countries during the 60-Co calibration procedure.
In the figure below, the chamber is shown during calibration. In Austria (left), it is positioned with the effective point of measurement in 5 cm depth (well, not really, but a correction is made so that the effect is the same). In Germany (right), the chamber's reference point (= the chamber axis) is positioned at 5 cm depth. The result is, that the calibration factor Nw in Germany is a little bit smaller than the Austrian Nw. By how much? By the factor pdis = 1 - 0.003 r, where r is the chamber's inner radius in millimeters.
For the Farmer, r = 3.05 mm, pdis = 1 - 0.003 * 3.05 = 0.9909 or NwGER = 0.9909 * NwAUT.
Logbook
| Date |
Event |
| 26.03.1996 |
S/N 811 and S/N 812: initial calibration by PTW. |
| 16.04.2013 |
S/N 812: Seibersdorf cannot determine saturation correction factor. Stabilization after voltage change takes too long. |
| 03.06.2014 |
Received new S/N 2601 and 2602 (cable length: 10 m). |
| 10.06.2014 |
Dropped S/N 2601: tip broken. |
| 11.06.2014 |
Both chambers sent to PTW for repair of S/N 2601 and reduction of cable length to 1.2 m. |
| 17.07.2014 |
Delivery of two new Farmer chambers: S/N 2591, S/N 2592 |
| 2026 |
Due to increasing costs for verification and calibration, we phased out Unidos 10396 in 2026. For the remaining electrometer/chamber combinations in use, we stopped ordering the correction factors ppol (60Co) and ps (60Co). These factors are very stable (see tables). |
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