Ion-recombination correction factor k

A. Piermattei, L. Azario, G. Arcovito, M.P. Toni

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Abstract

The large range of reference air kerma rates of brachytherapy sources involves the use of large-volume ionization chambers. When such ionization chambers are used the ion-recombination correction factor ksat has to be determined. In this paper three spherical ion chambers with volumes ranging from 30 to 104 cm3 have been irradiated by photons of a 192Ir source to determine the ksat factors. The ionization currents of the ion chambers as a function of the applied voltage and the air kerma rate have been analysed to determine the contribution of the initial and general ion recombination. The ksat values for large-volume ionization chambers obtained by considering the general ion recombination as predominant (Almond's approach) are in disagreement with the results obtained using methods that consider both initial and general ion-recombination contributions (Niatel's approach). Such disagreement can reach 0.7% when high currents are measured for a high-activity source calibration in terms of reference air kerma rate. In this study a new 'two-voltage' method, independent of the voltage ratio given by a dosimetry system, is proposed for practical dosimetry of continuous x- and gamma-radiation beams. In the case where the Almond approach is utilized, the voltage ratio V1/V2 should be less than 2 instead of Almond's limit of V1/V2 < 5.
Original languageEnglish
Pages (from-to)1025 - 1035
Number of pages11
JournalPhysics in Medicine and Biology
Volume41
Issue number6
DOIs
Publication statusPublished - Jun 1996
Externally publishedYes

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All Science Journal Classification (ASJC) codes

  • Radiological and Ultrasound Technology
  • Radiology Nuclear Medicine and imaging

Cite this

Piermattei, A., Azario, L., Arcovito, G., & Toni, M. P. (1996). Ion-recombination correction factor k. Physics in Medicine and Biology, 41(6), 1025 - 1035. https://doi.org/10.1088/0031-9155/41/6/006