Ionization chamber efficiency curves

Abstract

This paper describes the current status of ionization chamber efficiency curve modelling. Such curves, useful for ionization current prediction and for impurity corrections, cannot be obtained directly and are generally determined using empirical or Monte Carlo techniques. Each technique is described and practical examples are given. It is concluded that such models are a useful supplement to, rather than a replacement for, careful calibration and characterization measurements.

Simulation of the response of an ionization chamber to 214Bi emission. Application to the measurement of 222Rn

“…The objective was to check if the ampoule thickness could influence the response of the IC, by considering the high-energy electrons of the β transitions from the 222 Rn decay chain radionuclides. It must be highlighted that Pearce et al (2007) mentioned that "the simulation of IC response curves to beta emission is very sensitive to internal geometry of the IC and of the source, especially when the electron energy is high enough to cross all the layers and reach the gaseous sensitive volume". The results of the MC simulations of some 222 Rn daughter radionuclides highlight a systematic and non-negligible correlation between the IC gas ionization and the variation of the wall thickness of the ampoules used in measurements.…”

“…), and the shielding around (Ceccatelli et al, 2007;Kryeziu et al, 2007;Thiam et al, 2016). Generally, ICs are well adapted for solutions of gamma-emitting radionuclides (Amiot et al, 2012;Zimmerman and Judge, 2007) but can also be used for high-energy beta-emitting radionuclides such as 90 Y, although such measurements are more challenging (Pearce et al, 2007;Fenwick et al, 2014). In these cases, the IC response strongly depends on the transport of electrons in the radioactive solution and surroundings.…”

Uncertainty evaluation in activity measurements using ionization chambers

“…In [36], Gostely and Laedermann studied the effect of the vertical source position in the chamber as well as the thickness of different parts such as the electrodes or the re-entrant tube. The estimation is performed using the ratio of simulated and experimental efficiencies in [17,23,28,32] where a difference of 1%-2% is found or similarly in [30,36] and a difference of up to 5% is obtained.…”

Ionization chambers

“…ε i may be interpolated from the energy-dependent efficiency curve of the IC. The details of such a calculation procedure are presented elsewhere in this issue [4].…”

“…Many details about ionization chamber measurements and numerous publications from the early days of radioactivity measurements, until about 1995, can be found in the Monographie BIPM-4 [2]. Further aspects of IC measurements are examined by other authors in this special issue of Metrologia on radionuclide metrology: for example, comparisons of activity standards with the International Reference System (SIR) at the Bureau International des Poids et Mesures (BIPM) [3], energy-dependent efficiency curves [4] which need data of emission probabilities per decay [5,6] to calculate the radionuclide efficiency, traceability in nuclear medicine [7] and quality assurance with radionuclide calibrators. Radionuclide calibrators are composite systems incorporating both an IC and the associated electronics, which provide a direct reading in terms of activity.…”