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Design, fabrication and characterization of a windowless extrapolation chamber for low-energy X-rays: Experimental and Monte Carlo results
摘要： Extrapolation chamber is a special parallel-plate ionization chamber, particularly suggested for low penetrating radiations. Its sensitive volume is varied through a change of the inter-electrode distance, ideally satisfying the Bragg-Gray cavity theory. A windowless extrapolation chamber was designed and constructed for low-energy X-rays, produced at the tube voltage of 70-100 kV. It consists of the following elements and innovation. The electrodes of the chamber are made of a homogenous block of graphite instead of a coating graphite layer to reduce the leakage current. Also, the entrance window has been eliminated to decrease the beam perturbation. To the best of our knowledge, this type of chamber has not been used in low energy X-rays before. The performance of the chamber was investigated in terms of its saturation curve, polarity effect, leakage current, linearity of response and short-term stability. It was also simulated using Monte Carlo method and in the worst case, the relative ionization current obtained in experiment differs about 4.5% with that in the simulation result. Moreover, the influence of chamber components on its response was examined. All of the results showed the feasibility of its use for detection of 70 - 100 kV X-rays.
关键词： simulation,Low-energy X-rays,Monte Carlo,Extrapolation chamber,dosimetry
更新于2025-09-23 15:21:01
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Re-evaluation of the correction factors for the GROVEX
摘要： The GROVEX (GROssVolumige EXtrapolationskammer, large-volume extrapolation chamber) is the primary standard for the dosimetry of low-dose-rate interstitial brachytherapy at the Physikalisch-Technische Bundesanstalt (PTB). In the course of setup modifications and re-measuring of several dimensions, the correction factors have been re-evaluated in this work. The correction factors for scatter and attenuation have been recalculated using the Monte Carlo software package EGSnrc, and a new expression has been found for the divergence correction. The obtained results decrease the measured reference air kerma rate by approximately 0.9% for the representative example of a seed of type Bebig I25.S16C. This lies within the expanded uncertainty (k = 2).
关键词： dosimetry,ionisation chamber,extrapolation chamber,low-dose rate brachytherapy,primary standard
更新于2025-09-09 09:28:46