Characterization of tetramethylsilane for liquid-filled ionization dosimeters: Ion mobilities, free-ion yield and general recombination

Gago-Arias, Araceli; Argüeso, P.; Aguiar, Pablo; González‐Castaño, Diego M.; Gómez, F.; Pardo-Montero, Juan

doi:10.1016/j.nima.2015.03.007

Cited by 1 publication

(4 citation statements)

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“…The error bars for the experimental data represent the expanded uncertainty (k = 2, i.e., 95% coverage). The approximate dose‐per‐pulse on the top was calculated from Q 0 and the nominal sensitivity of the isooctane LIC (10.2 Gy/nC) and published scaling factors . It is merely intended to provide a more familiar scale to the reader.…”

Section: Resultsmentioning

confidence: 99%

“…The approximate dose-per-pulse on the top was calculated from Q 0 and the nominal sensitivity of the isooctane LIC (10.2 Gy/nC) 33 and published scaling factors. 21 It is merely intended to provide a more familiar scale to the reader. [Color figure can be viewed at wileyonlinelibrary.com] FIG.…”

Section: Discussionmentioning

confidence: 99%

“…The 2DR method uses the ratio of two measurements at different dose rates for calculating the charge inside the chamber, that is, after initial recombination and subsequently the saturation correction factor k s for volume recombination by extensive, but simple mathematics based on Eq. () . For sufficient precision, only dose rate ratios not smaller than 3 should be used.…”

Section: Methodsmentioning

confidence: 99%

“…Of the two LICs, one chamber was filled with 2,2,4-trimethylpentane (isooctane)the standard sensitive medium for this chamber typewhile the other chamber was a custom order filled with tetramethylsilane (TMS). TMS is of interest as an alternative sensitive medium, because it has an up to 2 times higher free ion yield than isooctane, resulting in increased sensitivity of the chamber 21 and shows also a slightly less energy dependence 22 . Both chambers have identical sensitive volumes with 2.5 mm diameter and a height of 0.35 mm.…”

Section: B Our Experimentsmentioning

confidence: 99%

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Correction for volume recombination in liquid ionization chambers at high dose‐per‐pulse

Götz

Tölli

et al. 2019

Medical Physics

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Purpose To determine the volume recombination at high dose‐per‐pulse in liquid ionization chambers (LIC) and to ascertain whether existing calculation methods verified in air‐filled chambers may be used to calculate a correction factor. Methods Two LICs, one filled with 2,2,4‐trimethylpentane (isooctane) the other with tetramethylsilane (TMS), were irradiated in a pulsed, 20 MeV electron beam. Via reference measurements with a Faraday cup, the saturation correction for volume recombination was determined for dose‐per‐pulse values ranging from about 5 mGy to 1 Gy for both chambers at a pulse duration of 693 ns. In addition, the isooctane chamber was irradiated with pulses of varying duration, ranging from 5 ps to 10 ms, at a dose‐per‐pulse of about 76.5 mGy. The dose‐per‐pulse‐dependent measurements were compared to calculations based on Boag's models (with and without a free electron fraction), the two‐dose‐rate method, and a numerical calculation. The pulse duration dependent measurements were compared only to a numerical calculation that iteratively calculates the charge transport and loss in a 1D model of an ionization chamber. Results In TMS only Boag's model with a free electron fraction and the numerical calculation are in good agreement with the experimental data. However, in isooctane, good agreement is observed between the experimental data, the numerical calculation as well as the two‐dose‐rate method, and Boag's model including a free electron fraction. Only Boag's model without a free electron fraction shows a good agreement with lesser extend. Furthermore, the pulse duration‐dependent data for isooctane are well described by the numerical model. Conclusion With isooctane as an active medium, a LIC could be directly used in a field with high dose‐per‐pulse utilizing the well‐established two‐dose‐rate method to correct the volume recombination. In addition, pulsed fields with variable pulse duration are easily modeled for this medium using a numerical calculation. Other media, as exemplified by the TMS‐filled chamber, might require additional considerations, such as including a fraction of free electrons in the consideration of volume recombination.

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: B Our Experimentsmentioning

confidence: 99%

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