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Ion recombination in liquid ionization chambers

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Department of Radiation Sciences Radiation Physics

Umeå University Umeå 2013

Umeå University Medical Dissertations, New Series No 1567

Ion recombination in

liquid ionization chambers

Development of an experimental method

to quantify general recombination

Jonas Andersson

Akademisk avhandling

som med vederbörligt tillstånd av Rektor vid Umeå universitet för

avläggande av filosofie doktorsexamen framläggs till offentligt försvar i

sal 260, byggnad 3A, Norrlands universitetssjukhus, fredagen den 31

maj, kl. 13:00. Avhandlingen kommer att försvaras på engelska.

Fakultetsopponent: Professor Anders Ahnesjö, Inst. för radiologi,

onkologi och strålningsvetenskap, Uppsala universitet

(2)

Organization

Document type

Date of publication

Umeå University Doctoral thesis 8 May 2013

Department of Radiation Sciences

Author

Jonas Andersson

Title

Ion Recombination in liquid ionization chambers - Development of an experimental method to quantify general recombination

Abstract

An experimental method (the two-dose-rate method) for the correction of general recombination losses in liquid ionization chambers has been developed and employed in experiments with different liquids and radiation qualities. The method is based on a disassociation of initial and general recombination, since an ionized liquid is simultaneously affected by both of these processes. The two-dose-rate method has been compared to an existing method for general recombination correction for liquid ionization chambers, and has been found to be the most robust method presently available.

The soundness of modelling general recombination in liquids on existing theory for gases has been evaluated, and experiments indicate that the process of general recombination is similar in a gas and a liquid. It is thus reasonable to employ theory for gases in the two-dose-rate method to achieve experimental corrections for general recombination in liquids. There are uncertainties in the disassociation of initial and general recombination in the two-dose-rate method for low applied voltages, where initial recombination has been found to cause deviating results for different liquids and radiation qualities.

Sensitivity to ambient electric fields has been identified in the microLion liquid ionization chamber (PTW, Germany). Experimental data may thus be perturbed if measurements are conducted in the presence of ambient electric fields, and the sensitivity has been found to increase with an increase in the applied voltage. This can prove to be experimentally limiting since general recombination may be too severe for accurate corrections if the applied voltage is low.

Keywords

General recombination, initial recombination, liquid ionization chamber, radiation dosimetry

Language

ISBN ISSN

Number of pages

English 978-91-7459-607-6 (Print) 0346-6612 86 + 4 papers

References

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