The Canadian Standard Free-Air Chamber for Medium Quality X-Rays

Henry, W H; Garrett, C.

doi:10.1139/p60-171

Cited by 5 publications

(6 citation statements)

References 4 publications

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“…More details can be found in the article by Henry and Garret. 19 The FAC geometry is modeled in full detail using the EGSnrc Cϩϩ library, 14 which allows the definition of complex geometry by means of user input, i.e., without having to resort to programming the geometry. A view of the chamber model employed in this investigation is shown in the lower panel of Fig.…”

Section: X-ray Tube and Fac Chamber Modelingmentioning

confidence: 99%

Novel approach for the Monte Carlo calculation of free-air chamber correction factors

2008

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A self-consistent approach for the Monte Carlo calculation of free-air chamber (FAC) correction factors needed to convert the chamber reading into the quantity air-kerma at the point of measurement is introduced, and its implementation in the new EGSnrc user code egs_fac is discussed. To validate the method, comparisons between computed and measured FAC correction factors for attenuation Ax, scatter (Ascat), and electron loss (Aeloss) are performed in the medium energy range where the experimental determination is believed to be accurate. The Monte Carlo calculations utilize a full simulation of the x-ray tube with BEAMnrc and a detailed model of the parallel-plate FAC. Excellent agreement between the computed Ascat and Aeloss and the measured values for these correction factors currently used in the National Research Council (NRC) of Canada primary FAC standard is observed. Our simulations also agree with previous Monte Carlo results for Ascat and Aeloss for the 135 and 250 kVp Consultative Committee for Ionizing Radiation reference beam qualities. The computed attenuation correction agrees with the measured Aatt within the stated uncertainties, although the authors' simulations demonstrate that the evacuated-tube technique employed at NRC to measure the attenuation correction slightly overestimates Aatt in the medium energy range. The newly introduced corrections for backscatter, beam geometry, and lack of charged particle equilibrium along the beam axis are found to be negligible. On the other hand, the correction for photons leaking through the FAC aperture, currently ignored in the NRC standard, is shown to be significant.

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Section: X-ray Tube and Fac Chamber Modelingmentioning

confidence: 99%

Novel approach for the Monte Carlo calculation of free-air chamber correction factors

2008

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“…These calculations showed efficiency increases of 2 to 5 times when using range re- Henry and C. Garret. 135 The LEES is almost identical in design to the MEES, but much smaller.…”

Section: ^ W X E T N En {E T )mentioning

confidence: 98%

“…Upper panel: Schematic horizontal sectional view of the MEES used at NRC. Taken from the paper by B. Henry and C. Garret 135. Lower panel: Sectional view of the geometrical model of the MEES visualized using egs_view, the egs++ geometry viewer.4.4.…”

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confidence: 99%

Efficient Monte Carlo simulations in kilovoltage x-ray beams

Hing¹

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“…The x ray beam is generated with a Comet MXR-320 x ray tube (Liebefeld, Swizerland). The x ray tube is control by a system with current and voltage stabilizer [8].…”

Section: Chapter 5 Validationmentioning

confidence: 99%

“…2 is a schematic diagram of a conventional free air chamber, which is currently used as the primary standard of air kerma of low and medium energy x ray at NRC. Detail descriptions of this instrument can be found in the report of Henry and Garrett[8].…”

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confidence: 99%

Commissioning of the Canadian Primary Standard for Low Dose Rate Brachytherapy

Shen¹

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The purpose of this project is to investigate the performance of the NRC WAFAC and commission it as a primary standard for calibrating LDR sources. Significant enhancements were implemented to the WAFAC for improving signal to noise ratio, measurement reproducibility and eliminating electric field distortion. The validation of the WAFAC, comparing to the existing NRC primary standard, shows that the agreement between the two devices is within the combined measurement uncertainties of less than 0.5 %. The measurements made with a 125 I LDR seed gave results that were consistent at the 1 % level with the manufacturer's stated seed activity (traceable to NIST). The polarity effect and aperture size effect had been studied during the commissioning. The overall k = 2 standard uncertainty in the determination of air kerma strength using the NRC WAFAC is estimated to be 2.6 %, which reaches the target uncertainty for the standard. iii I would like to extend my appreciation to Dr. Dave Rogers for his encouragements, help and belief in me. I would also like to extend my appreciation to Dr. Dave Wilkins for providing me free I-125 seeds. I would also like to extend my appreciation to Dr. Ernesto Mainegra-Hing for his Monte Carlo simulations and discussions with me. I would additionally like to thank Mr. Stewart Walker, Mr. David Marchington, and Mr. Brad Downton for their assistance in electrical and mechanical matters. Finally I would like to extend my deepest gratitude to my wife Meilin and my son Yiwen. Without their love, support and understanding I could never have completed my graduate studies.

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The Canadian Standard Free-Air Chamber for Medium Quality X-Rays

Abstract: A description is given of the Canadian standard free-air chamber for measurement of medium quality X-rays, including measurements of the contribution from radiation scattered from the air and from the diaphragm, and a method for the accurate alignment of the chamber and X-ray source.

Cited by 5 publications

References 4 publications

Novel approach for the Monte Carlo calculation of free-air chamber correction factors

Novel approach for the Monte Carlo calculation of free-air chamber correction factors

Efficient Monte Carlo simulations in kilovoltage x-ray beams

Commissioning of the Canadian Primary Standard for Low Dose Rate Brachytherapy

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