Ionisation Chambers
Ionisation chambers are well-established for the dosimetry of ionising radiation. The measurement of the chamber current or the produced electric charge over the measurement time combined with the medium ionisation energy enables the conclusion of the energy deposited in the chamber volume, which is to say the energy dose. Different air-filled ionisation chambers are on hand for the measurement free in air in the Radiation Physics Group.
Chambers for the measurement of high-energy photon radiation
PTW cylinder stem chamber
Cylinder stem chamber with build-up cap
from PTW Freiburg
PTW spherical chamber TK30
Spherical chamber TK30 from
PTW Freiburg
These chambers are constructed for the measurement of Air-Kerma rate or of the photon ambient dose equivalent rate. They are used for absolute dosimetry in photon fields and for the calibration of other dosimetry systems. On hand are a 30 cm³ cylinder stem chamber and a spherical chamber TK30 Typ 32005 from PTW-Freiburg. A Unidos webline, too from PTW-Freiburg, is used for charge or current measurement with all chambers.
Chambers for photon and electron radiation
Chamber OD-01 K
Ionisation chamber OD-01 K
from STEP Sensortechnik und Elektronik Pockau
For the measurement of ambient and directional dose equivalent rate, we have a large volume chamber type OD-01 K from STEP- Sensortechnik und Elektronik Pockau. This chamber has a volume of 600 cm3 and is thus suited for the measurement at low radiation intensities. By removing the build-up cap, the measured quantity can be switched from ambient to directional dose equivalent rate.
Chambers for low energy photon and electron radiation
The so-called extrapolation chamber (following Böhm) from PTW-Freiburg is a special ionisation chamber. For this type, the chamber size can be varied precisely. By measuring the chamber current for different chamber depths and extrapolating to zero depth, the dose on this surface is evaluated. Such arrangements are especially qualified for the dosimetry of low energy photon and electron radiation. These are i.e. X-ray tubes with acceleration voltages above 7.5 keV and electron emitters of (medium) energies above 5 keV.
Extrapolation chamber following Böhm
Extrapolation chamber following Böhm from PTW-Freiburg
Moreover, with an extrapolation chamber the investigation of dose buildup at boundary layers or surfaces is possible. By inserting absorbing layers between source and chamber, the dose rate in different depths in material can be analysed. This enables the measurement of i.e. the directional dose equivalent in 7 mg/cm².
For questions and remarks concerning this web page please send email to: PD Dr. J. Henniger
Last Update: 09. 12. 2016
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