Ion recombination correction factor in scanned light-ion beams for absolute dose measurement using plane-parallel ionisation chambers
Based on international reference dosimetry protocols for light-ion beams, a correction factor ( k s ) has to be applied to the response of a plane-parallel ionisation chamber, to account for recombination of negative and positive charges in its air cavity before these charges can be collected on the...
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| Main Authors: | , , , , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
12 June 2017
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| In: |
Physics in medicine and biology
Year: 2017, Volume: 62, Issue: 13, Pages: 5365-5382 |
| ISSN: | 1361-6560 |
| DOI: | 10.1088/1361-6560/aa730f |
| Online Access: | Verlag, Volltext: http://dx.doi.org/10.1088/1361-6560/aa730f Verlag, Volltext: http://stacks.iop.org/0031-9155/62/i=13/a=5365 
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| Author Notes: | S. Rossomme, J. Horn, S. Brons, O. Jäkel, A. Mairani, M. Ciocca, V. Floquet, F. Romano, D. Rodriguez Garcia, S. Vynckier, H. Palmans |
| Summary: | Based on international reference dosimetry protocols for light-ion beams, a correction factor ( k s ) has to be applied to the response of a plane-parallel ionisation chamber, to account for recombination of negative and positive charges in its air cavity before these charges can be collected on the electrodes. In this work, k s for IBA PPC40 Roos-type chambers is investigated in four scanned light-ion beams (proton, helium, carbon and oxygen). To take into account the high dose-rates used with scanned beams and LET-values, experimental results are compared to a model combining two theories. One theory, developed by Jaffé, describes the variation of k s with the ionization density within the ion track (initial recombination) and the other theory, developed by Boag, describes the variation of k s with the dose rate (volume recombination). Excellent agreement is found between experimental and theoretical k s -values. All results confirm that k s cannot be neglected. The solution to minimise k s is to use the ionisation chamber at high voltage. However, one must be aware that charge multiplication may complicate the interpretation of the measurement. For the chamber tested, it was found that a voltage of 300 V can be used without further complication. As the initial recombination has a logarithmic variation as a function of 1/ V , the two-voltage method is not applicable to these scanned beams. |
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| Item Description: | Gesehen am 25.04.2018 |
| Physical Description: | Online Resource |
| ISSN: | 1361-6560 |
| DOI: | 10.1088/1361-6560/aa730f |