A liquid ionisation chamber for neutron dosimetry

Abstract

Theories of ionisation in liquid and the use of liquid ionisation chambers in mixed neutron field dosimetry have been studied. Theoretical models developed by Jaffe and by Onsager were used for comparison with the experimental measurements. The Jaffe method predicts a higher collecting efficiency than does the Onsager model. Gamma and neutron sensitivities of a liquid chamber can be calculated by the Bragg-Gray principle and Onsager's theory. The calculation is subject to relatively large uncertainties, mainly due to insufficient knowledge of the ion distribution in ionisation tracks and of W/e values for iso-octane. The chamber constructed for clinical use should work best for mixed neutron fields with gamma-neutron ratios of 10-20%; however, it would be difficult to use a liquid ionisation chamber to detect small neutron variations in mixed fields with large gamma components.

Liquid ionization chamber initial recombination dependence on LET for electrons and photons

“…Blanc et al (1965) used liquid ionization chambers (LICs) and developed an experimental method to distinguish between radiation qualities with differences in LET. This method was later used by several authors (Ladu and Pelliccioni 1966, Charalambus 1967, Nakayama and Kawano 1970, Bednarek et al 1976, Chu et al 1980. However, the method was only shown to distinguish between radiation qualities with large differences in LET, e.g.…”

General collection efficiency in liquid iso-octane and tetramethylsilane used as sensitive media in a thimble ionization chamber

“…This effect is in direct contrast to the situation in a gas ionization chamber, for example filled with air, where the initial recombination loss is less than 1% at atmospheric pressure and an electric field strength of 1 × 10 4 V m −1 (Scott and Greening 1963, Böhm 1976a, b, Takata 1994. With constant radiation and negligible general recombination, the ionization current in a dielectric liquid will increase linearly with increasing field strength (Jaffé 1906, Bednarek et al 1976, Chu et al 1980, Bartczak and Hummel 1986, Wickman and Nyström 1992. The characteristic relation between the ionization current from an irradiated dielectric liquid and the electric field strength is shown in figure 1.…”

Energy spectrum and absorbed dose in water for d+T neutron irradiation

“…In the past two decades, absorbed doses and radiation quality have been measured and calculated for medical and biological applications in a phantom under simulated irradiation conditions. Measurements of dose distributions using a variety of dosimetric techniques have been carried out by Broers-Challiss et a1 (1973), Bewley et ai (1974), Greene and Major (1974), Mijnheer et ai (1974), Broerse (1977), and Chu et al (1980). Calculations in particular irradiation geometries have been reported by Frigerio et a1 (1973), Krishnaswamy (1974), Jones (1974), Ing and Cross (1975), and Shapiro and Lin (1976).…”