Measurement of gamma and beta radiation doses by means of thimble ionization chambers

Summary The above experimental investigations of secondary electrons produced in thick layers of substances, serve to obtain a deeper understanding of the essence of the processes which take place in gamma radiation detectors, and to arrive at several conclusions about their efficient use.     

Calorimeter tests with liquid ionization chambers

Configurations of sampling calorimeters with iron, lead and uranium as absorbers have been investigated using liquid ionization chambers as active elements. As liquid tetramethylsilane has been used. Results of beam tests with electrons, pions and muons in the energy range of 2 to 6 GeV are presented and compared with Monte Carlo simulations. In particular the questions regarding which configuration can compensate and the separation of sampling from intrinsic fluctuations have been studied.     

High rate operation of warm-liquid ionization chambers

The effect of positive ion buildup at high rates in warm-liquid ionization chambers is considered. Measurements made with TMS indicate that warm liquids can operate at SSC particle fluxes.     

The physics and chemistry of room-temperature liquid-filled ionization chambers

The properties of excess electrons in non-polar liquids, such as tetramethylsilane and 2,2,4,4-tetramethylpentane, which are suitable for room-temperature liquid-filled ionization chambers are reviewed. Such properties as mobility, ionization yield, conduction band energy, trapping, and the influence of the electric field are considered.     

Potential of gel walled high pressure ionization chambers for high energy neutron dosimetry

Theoretical examination of initial recombination of ions in muscle equivalent gel, walled high pressure ionization chambers for neutrons of 5–30 MeV indicates the potential of such instruments to measure both the neutron and gamma ray absorbed doses in high energy mixed neutron-gamma radiation fields currently used for neutron therapy.     

Liquid ionization chambers with electron extraction and multiplication in the gaseous phase

Electrons have been transferred from liquid to gaseous argon with an estimated efficiency of 100%. Electron extraction has also been accomplished in liquid 2,2,4,4-TMP with parallel plate amplification in the gas of over 10³.     

Impact of space charges on the saturation curves of ionization chambers

We apply a perturbation method to quantify the impact of space charge accumulation on the output current of ionization chambers. We then obtain the formulae of the saturation curves delivered by these detectors under the form of series for which we calculate the first coefficients. The spatial variations of the primary charge density are taken into account in the calculations. For uniform ionization rates, we demonstrate that the amplitude of the space charge perturbations depends only on the values of the electronic and ionic Langevin factors of the filling fluid. We show that the influence of space charges can be neglected when the Langevin factor, λ, is small. These results were confirmed using numerical resolutions of the charge propagation equations. Finally, we evaluate the voltage that delimits the transition between the recombination regime and the saturation plateau when the space charges are taken into account.     

Physical parameters and correction factors for ionization chambers for absolute measurement of air kerma in γ-ray fields

Values of physical parameters and correction factors essential for the absolute measurement of air kerma in ¹³⁷Cs and ⁶⁰Co γ-ray fields were obtained using an EGS5 program for spherical, cylindrical and pancake ionization chambers. The mean mass collision stopping power ratio for graphite and air, was found to vary depending on the cutoff energy of electrons employed in calculation. The ratio between the energies deposited in cavity air due to Compton electrons emitted from the air and those from the graphite wall increases as the chamber size is increased. It also increases as the γ-ray energy is reduced and is equal to 0.09 for ¹³⁷Cs γ-rays in a spherical ionization chamber of cavity diameter 12 cm. Correction factors for γ-ray attenuation in chamber walls and those for the contribution of scattered γ-rays to chamber responses were obtained separately. The wall correction factor, which is equal to the product of these two factors, is close to unity for pancake chambers.     

The analysis of delayed neutron energy spectra recorded with 3He ionization chambers

Details of the neutron detection efficiency of ³He ionization chambers have been clarified. The usefulness of pulse rise-time analysis has been explored for the example of the ¹⁷N delayed neutron spectrum. Because of obvious disadvantages, this method has been rejected, however, in favour of a complete response correction that removes all others than ³He(n,p)³H events with great precision without disturbing the efficiency function. Peak fitting analysis is applied to structured delayed neutron spectra, and its physical significance is discussed.     

Application of the Shockley-Ramo theorem on the grid inefficiency of Frisch grid ionization chambers

The concept of grid inefficiency in Frisch grid ionization chambers and its influence on the anode pulse shape is explained in terms of the Shockley-Ramo theorem for induced charges. The grid inefficiency correction is deduced from numerically calculated weighting potentials. A method to determine the correction factor experimentally is also presented. Experimental and calculated values of the correction factor are shown to be in good agreement.     

Electron fluence perturbation by gap-shaped and by cylindrical gas-filled ionization chambers with axes normal to the beam

For electron beam absorbed dose measurements using gas-ionization chamber, a perturbation correction factor has been defined to correct for the disturbance of the fluence. For a gap-shaped cavity, a revised perturbation factor is derived. The range of validity of the calculations is extended over that of a previous study. The direct calculations for cylindrical cavities are very difficult. Instead, the form of the cylinder is approximated by a square parallelepiped. Comparison with Monte Carlo calculations showed good agreement.     

Semiconductor drift chambers for position and energy measurements

Semiconductor drift chambers have been recently suggested and feasibility tests performed. This paper presents the first operative silicon drift detectors for position and energy measurements. Design criteria and experimental results in the laboratory and on an accelerator beam are reported.     

The readout method for wire chambers

The method for readout of information from a wire chamber through a conventional conductive wire cathode is tested to study the possibility of its practical usage. It is observed that the value of the signal induced on an external readout electrode depends on the detector geometry and makes up approximately 5–10% of the anode signal value. The application of this method should permit one to separate a detector into an active device and an independent readout system as well as to make the readout system more flexible and to improve detector coordinate properties.     

Large drift chambers for future detectors

The design and construction of simple and stable drift chambers, suited for production in large quantities and sizes, is presented. These chambers are under construction for the muon detector of the L3 experiment at LEP.