Digitala Vetenskapliga Arkivet

Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
A comparison of different experimental methods for general recombination correction for liquid ionization chambers
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
Show others and affiliations
2012 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 21, p. 7161-7175Article in journal (Refereed) Published
Abstract [en]

Radiation dosimetry of highly modulated dose distributions requires a detector with a high spatial resolution. Liquid filled ionization chambers (LICs) have the potential to become a valuable tool for the characterization of such radiation fields. However, the effect of an increased recombination of the charge carriers, as compared to using air as the sensitive medium has to be corrected for. Due to the presence of initial recombination in LICs, the correction for general recombination losses is more complicated than for air-filled ionization chambers. In the present work, recently published experimental methods for general recombination correction for LICs are compared and investigated for both pulsed and continuous beams. The experimental methods are all based on one of two approaches, either measurements at two different dose rates (two-dose-rate methods), or measurements at three different LIC polarizing voltages (three-voltage methods). In a comparison with the two-dose-rate methods, the three-voltage methods fail to achieve accurate corrections in several instances, predominantly at low polarizing voltages and dose rates. However, for continuous beams in the range of polarizing voltages recommended by the manufacturer of the LICs used, the agreement between the different methods is generally within the experimental uncertainties. For pulsed beams, the agreement between the methods is poor. The inaccuracies found in the results from the three-voltage methods are associated with numerical difficulties in solving the resulting equation systems, which also make these methods sensitive to small variations in the experimental data. These issues are more pronounced for the case of pulsed beams. Furthermore, the results suggest that the theoretical modelling of initial recombination used in the three-voltage methods may be a contributing factor to the deviating results observed.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2012. Vol. 57, no 21, p. 7161-7175
Keywords [en]
General recombination, initial recombination, liquid ionization chamber, radiation dosimetry, two-dose-rate method, three-voltage method, isooctane, tetramethylsilane
National Category
Other Physics Topics Radiology, Nuclear Medicine and Medical Imaging
Research subject
radiation physics
Identifiers
URN: urn:nbn:se:umu:diva-60453DOI: 10.1088/0031-9155/57/21/7161Scopus ID: 2-s2.0-84868024299OAI: oai:DiVA.org:umu-60453DiVA, id: diva2:560338
Available from: 2012-10-19 Created: 2012-10-13 Last updated: 2023-03-23Bibliographically approved
In thesis
1. Ion recombination in liquid ionization chambers: development of an experimental method to quantify general recombination
Open this publication in new window or tab >>Ion recombination in liquid ionization chambers: development of an experimental method to quantify general recombination
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2013. p. 76
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1567
Keywords
General recombination, initial recombination, liquid ionization chamber, radiation dosimetry
National Category
Other Physics Topics Radiology, Nuclear Medicine and Medical Imaging
Research subject
radiation physics
Identifiers
urn:nbn:se:umu:diva-68942 (URN)978-91-7459-607-6 (ISBN)978-91-7459-608-3 (ISBN)
Public defence
2013-05-31, Sal 260, by 3A, Norrlands universitetssjukhus, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2013-05-08 Created: 2013-04-30 Last updated: 2018-06-08Bibliographically approved

Open Access in DiVA

No full text in DiVA

Other links

Publisher's full textScopus

Search in DiVA

By author/editor
Andersson, JonasTölli, Heikki
By organisation
Radiation Physics
In the same journal
Physics in Medicine and Biology
Other Physics TopicsRadiology, Nuclear Medicine and Medical Imaging

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 830 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf