Liquid-Filled Ionization Chambers

Combining the advantages of air-filled ion chambers and
solid state detectors

How they work

Liquid-filled ionization chambers work according to the same principles as conventional air-filled ionization chambers: They consist basically of two conducting electrodes in a sealed container filled with a suitable liquid. Ionizing radiation creates positive and negative charge carriers which move in opposite directions, thereby producing a current which can be measured by an electrometer (see Fig. 2).

The liquid filling has a density roughly 1000 times greater than air as used in air-filled ion chambers (Fig. 1). It must be highly insultating to avoid leakage currents. Typical polarizing voltages are in the range of  400 - 1000 V.


The advantages they offer for use in high-radiation dosimetry   

  • High spatial resolution and strong signal
    Due to the higher ionization density of liquids compared to air, liquid ion chambers have a very small sensitive volume and still yield a high response.

  • Good energy response in the keV-range
    The response to low energy scattered photons is almost as water equivalent as for diamond detectors.

  • Very good energy response in the MeV-range
    The ratio of the mass stopping power to water varies only by 4.5 % in the range from 0.1 to 20 MeV whereas diamond and air vary by 2 % and 16 % respectively.

  • No air-density correction needed
    Liquids can be considered as incompressible compared to air.

  • Almost negligible directional dependence
    Contrary to diodes,  liquid-filled ion chambers show a very low directional dependence.

  • Long-term stability
    Ionization chambers are known to be stable over a long period of time. Compared to diodes, the liquid filling is less prone to ageing or degradation (see publication on long-term stability of liquid ionization chambers by Jalil Bahar-Gogani et al. listed on the right).

  • Made of water equivalent materials
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Fig. 1: Basic principle of operation of an air-filled ion chamber
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Fig. 2: Basic principle of operation of a liquid-filled ion chamber

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