Liquid ionization chambers

The most prominent application of nonpolar liquids is their use as detection media in liquid ionization chambers for ionizing radiation. The concept of a liquid-filled conductivity cell for the detection of radioactive radiation or X-rays was first realized almost 100 years ago. In 1897, J.J. Thomson reported that vaseline oil showed an increase in electrical conductivity under irradiation with X-rays (Thomson, 1897). A few years later, P. Curie studied the influence of radium radiation on the electrical conductivity of several nonpolar liquids (Curie, 1902). Later, gas-filled ionization chambers and counters and solid-state devices became the dominating detectors for ionizing radiation and elementary particles. 

With the advancement in the understanding of the interaction of radiation and liquids and with improvements in manufacture and purification of liquids, the application of liquid ionization chambers for dosimetry and for detection of elementary particles has received increasing interest. Another promising development are imaging chambers for medical physics and materials testing. 

Basically, two modes of operation of a liquid ionization chamber can be distinguished (1) ion current measurement and (2) electron pulse detection and counting. Ion current chambers are used in medical physics for dosimetry and radiation field mapping, while electron pulse chambers are employed in the detection of individual elementary particles and quanta in radiation and high energy physics. 

In each layer of thickness dx at x recombination leads to a loss of charge per cm s given as 

In a volume of 1 cm cross section and length d, the total loss of charge due to volume recombination is obtained as 

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Abstract An iron sampling calorimeter with warm-liquid ionization chambers has been tested at the CERN SPS in order to study the signal development and to verify the energy calibration of the hadron calorimeter in the KASCADE-Grande air shower experiment. The signal calibration of the detectors is discussed. First results of the analysis of the longitudinal shower development in the calorimeter are presented and compared with results from simulations based on the GEANT/ FLUKA code. 

Fig. 13. Sn K edge XANES Spectra from simultaneous optical (luminescence) and ion yield measurements of an anthracene/toluene solution (1 g/1) of tetramethytin (0.5 ml (CHjl Sn in 20 ml solution) in a parallel plate liquid ionization chamber at various voltages across the electrodes. The separation ot the electrodes and the length of the cell are 3 mm and 2 cm respectively...

The radiation-induced conductivity of nonpolar liquids is of fundamental and practical interest. Ionization is one of the primary processes in the interaction of high-energy radiation and matter. From the measurement of the radiation-induced conductivity, information on the spatial distribution of the ionization events along the path of the ionizing particle can be obtained. From a practical point of view, liquid ionization chambers have received increasing attention in high-energy physics and medical physics where they supplement other types of detectors. 

Under these conditions, the radiation-induced current is proportional to the dose rate. The dependence of of the field E is reflected by the dependence of the apparent charge carrier yield Gfi(E) on the field. Equation 21 is equivalent to the finding that in gas ionization chambers the saturation current is proportional to the dose rate. The realization of this condition is a prerequisite for the application of liquid ionization chambers as dosimeters (see Chapter 9). 

Givemaud, A., Monte Carlo simulation of calorimeters based on liquid ionization chambers, in 2nd Int. Conf. on Calorimetry in High Energy Physics, Capri, Italy, Ereditato, A., Ed., World Scientific, 1991. 

Homeck, E, Properties of a liquid ionization chamber irradiated with fast neutrons, in Dosimetry in Agriculture, Industry, Biology and Medicine, International Atomic Energy Agency, Vienna, 1973. 

A disadvantage of ionic liquid ionization chambers is their sensitivity to mechanical shocks. This effect becomes especially disturbing if the chambers are to be used in radiation protection, since low ionization currents are involved. 

Figure 2 Liquid ionization chamber with Frisch grid. (Redrawn from Bunemann, O., Cran-shaw, T.E., and Harvey, J.A., Can. J. Res., 27,191,1949.)...

Liquid ionization chambers form the basis for detectors which are designed to produce an electronic image of individual tracks of ionizing particles or quanta or which are to serve as substitutes for radiation-sensitive film in medical diagnostics. 

A standard instrument in hi energy physics experiments is the liquid argon calorimeter with absorber plates from heavy metals (iron, lead, uranium). The liquid ionization chambers usually have electrode separations of 1 or 2 mm and operate at field strengths of several kV/cm. This leads to electron collection times in the submicrosecond time domain (Engler, 1984 Fabjan, 1985). Liquid argon of sufficient purity (oxygen impurity level approximately 1 ppm) from a storage tank is evaporated and recondensed into the calorimeter. No additional purification is necessary. 

Anderson, D. F. and Holroyd, R. A., High rate operation of warm-liquid ionization chambers, Nucl Instrum. Methods, A260, 343,1987. 

Engler, J., Liquid ionization chambers at room temperatures, J. Phys. G Nucl. Part. Phys., 22, 1,1996. 

Ochsenbein, S., Schinzel, D., Gonidec, A., and Schmidt, W. E, Purity in room temperature liquid ionization chambers, Nucl. Instrum. Methods, A273, 654,1988. 

The field of liquid ionization chambers received a fresh impulse because of the interest expressed by Prof. Carlo Rubbia, and Dr. Dieter Schinzel who initiated at CERN, the European High Energy Physics Laboratory at Geneva, a vigorous program on electron pulse chambers to which I had the good fortune of contributing for one year and a half in 1986/87. 

CHARGE RECOMBINATION IN ROOM TEMPERATURE LIQUID IONIZATION CHAMBERS... 

Pb(CH3)4 vapor has been used to fill Geiger counters [170 to 174], and was suggested for use in liquid ionization chambers [175]. Short-lived transients are generated by pulse radiolysis of Pb(CH3)4 dosed with naphthalene and toluene, which can be employed for time-resolved dosimetry of low-energy X-rays [176]. 

Pb(C2H5)4 vapor was suggested for use in liquid ionization chambers [506], and in a dosimeter in the low-energy X-ray region [515]. 

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