Ion loss due to initial recombination in a parallel-plate cavity ionization chamber

Takata, N.

doi:10.1088/0031-9155/39/6/009

Cited by 9 publications

(8 citation statements)

References 8 publications

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“…In the present work, we use the following equation to correct for initial recombination. This equation was found to give close approximations to experimental data on initial recombination loss obtained for a parallel-plate ionization chamber irradiated with y-rays (Takata 1994).…”

Section: Calculation Of M Valuessupporting

confidence: 58%

“…The humidity-control system was similar to that employed in another experiment, which was performed subsequently (Takata 1994). Dry air was obtained by passing the stream through a trap, which was cooled to -40°C to -60°C.…”

Section: Methodsmentioning

confidence: 99%

“…A value (4.4 f 1.5 V m-') was obtained for El by Bohm using p-rays. It is known, however, that equation ( 3) is valid only at high electric field strengths (Takata 1994).…”

Section: Calculation Of M Valuesmentioning

confidence: 99%

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The effects of humidity on volume recombination in ionization chambers

Takata¹

1994

Phys. Med. Biol.

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Saturation curves were measured with a parallel-plate ionization chamber for air with humidities of 0%-81%. From the curves, values of m--which is equal to (alpha/eK+ K-)1/2 where alpha is the recombination coefficient, e the charge of an ion, and K+ and K- are mobilities of positive and negative ions, respectively-were obtained. It was confirmed that humidity was the decisive cause of the increase in the value of m with the lifetime of ions in the ionization chamber. It was found that the value of m increases sharply in a range of small values of the product of the ion lifetime and the partial pressure of water vapour and increases more slowly at high values of this parameter.

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Section: Calculation Of M Valuessupporting

confidence: 58%

Section: Methodsmentioning

confidence: 99%

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The effects of humidity on volume recombination in ionization chambers

Takata¹

1994

Phys. Med. Biol.

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“…These reference values are plotted together in figure 4. As well, Boutillon (1998) showed values of 9.6 to 13.5 V m −1 between 1.3 × 10 −10 and 2.5 × 10 −8 A m −1 , and Takata (1994) obtained values at 0.2-0.9 nA m −1 . It is interesting enough to note that all the data were aligned along a straight line by the least-squares method, as shown in the figure.…”

Section: E 1 Of Initial Recombinationmentioning

confidence: 68%

Ion recombination in parallel-plate free-air ionization chambers for synchrotron radiation

Nariyama

2006

Phys. Med. Biol.

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The saturation characteristics of two sizes of parallel-plate free-air ionization chambers were investigated for synchrotron radiation at bending-magnet, wiggler and undulator beamlines of SPring-8. The gaps of the electrodes were 4.2 and 85 mm. The monoenergetic photon energies ranged from 10 to 115.56 keV and the air kerma rates from 0.2 mGy s-1 to 150 kGy s-1. Ion recombination at the high dose rate was found to be smaller than that predicted by Boag's expression, which was based on volume recombination, and the difference increased with an applied electric field. In the high dose rate region, the reciprocal of the current was linear to the reciprocal of the electric field near saturation, which represented the occurrence of initial recombination and diffusion loss. At the low electric field and the low dose rate, the reciprocal of the current was linear to the reciprocal of the square of the electric field. The reduction of total ion recombination was attributed to the shift of the contribution from volume recombination to initial recombination and diffusion loss.

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“…However, some factors lead to the lack of complete collection of these charges [ 9 ]. These factors are related to different origins either connected with the geometrical structure of the ion chamber, applied voltage, or the beam type and strength [ 10 , 11 ].…”

Section: Introductionmentioning

confidence: 99%

Efficiencies of Some Spherical Ion Chambers in Continuous and Pulsed Radiation: A Numerical Evaluation

Maghraby

2015

Pol J Radiol

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SummaryBackgroundEvaluation of the collection efficiencies of ion chambers is a necessity for the proper evaluation of radiation quantities in different applications. Overall collection efficiency is the product of three different values: collection efficiencies considering contributions of, volume recombination, back-diffusion loss and initial recombination, the later may be neglected at low charge rates.Material/MethodsFive common spherical ion chambers of different volumes and specifications were included in this study for the evaluation of volume recombination collection efficiency and back diffusion collection efficiency for continuous and pulsed radiation and at different values of the applied polarizing potential. Through current work there is an attempt of focusing on how the selection of ion chamber dimensions may affect the overall collection efficiency in addition to the proper selection of other influencing parameters.ResultsCollection efficiencies considering volume recombination (fv) for five spherical ion chambers of common types were evaluated for continuous and pulsed radiation over a wide range of polarizing potential. The relation between the ion chamber volume and its evaluated collection efficiencies were studied for both continuous and pulsed radiation; transit time values for the ion chambers included in this study were evaluated at different values of applied potential. Also, collection efficiencies considering diffusion current values (fd) were evaluated for the five chambers, and plotted versus the applied polarizing potential.ConclusionsThrough this study it was feasible to evaluate numerically the collection efficiencies of some spherical ion chambers considering volume recombination and back diffusion effects; the affecting parameters were studied and highlighted.

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Ion loss due to initial recombination in a parallel-plate cavity ionization chamber

Cited by 9 publications

References 8 publications

The effects of humidity on volume recombination in ionization chambers

The effects of humidity on volume recombination in ionization chambers

Ion recombination in parallel-plate free-air ionization chambers for synchrotron radiation

Efficiencies of Some Spherical Ion Chambers in Continuous and Pulsed Radiation: A Numerical Evaluation

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