Pixel sensitivity variation in a CdTe-Medipix2 detector using poly-energetic x-rays

We have a 1-mm-thick cadmium telluride (CdTe) sensor bump-bonded to a Medipix2 readout chip. This detector has been characterized using a poly-energetic x-ray beam. Open beam images (i.e. without an attenuating specimen between the x-ray source and the detector) have been acquired at room temperature using the MARS-CT system. Profiles of various rows and columns were analyzed for one hundred, 35-ms exposures taken with a bias voltage of -300 V (operating in electron collection mode). A region of increased sensitivity is observed around the edges of the detector. A reasonably periodic, repeatable variation in pixel sensitivity is observed. Some small regions with very low sensitivity and others with zero signals are also observed. Surrounding these regions are circular rings of pixels with higher counts. At higher flux (higher tube current in the x-ray source) there is evidence of saturation of the detector assembly. In this paper we present our understanding of the origin of these features and demonstrate the improved image quality obtained after correcting for these variations

CVD Diamond X-ray Detectors for Radiotherapy Dosimetry

X-ray detectors were fabricated from a range of commercially-available synthetic diamond fabricated using chemical vapour deposition (CVD). As these detectors are intended as dosimeters for use in radiotherapy (beam calibration and profiling, in-situ dose measurements etc.), they were appropriately packaged and tested in a clinical environment, using clinical apparatus and following clinical procedures. The combination of linear dose-rate dependence of the photocurrent, negligible dark current levels (pA or less, compared to nA photocurrents), low priming doses (few Gy) and high specific sensitivities (of up to 460 nCGy-1mm-3, compared to reported values of 50–140 nCGy-1mm-3 for a commercial natural diamond-based X-ray detector) demonstrates the potential of these devices as simple–to–use, small size, tissue-equivalent, sensitive X-ray dosimeters

Suitability of synthetic diamond films for x-ray dosimetry applications

Simple sandwich-type device structures have been fabricated by deposition of metal contacts on opposing faces of polycrystalline diamond films synthesised using chemical vapour deposition. The electrical characteristics of these devices have been investigated during exposure to a 6 megavolt photon beam from a clinical linear accelerator. The photocurrent appears to vary as the dose rate to the power of 0.78-0.85. The angular dependence of the photocurrent is less than 10 per cent. Further study on a range of CVD diamond substrates from different manufacturers is on-going

Investigation of the suitability of commercially-available CVD diamond for megavoltage x-ray dosimetry

Note the addition of an erratum to “Investigation of the suitability of commercially available CVD diamond for megavoltage X-ray dosimetry”, added to the end of the full-text article.Sandwich-type X-ray detectors were fabricated on commercially available chemical vapour deposition diamond sourced from three manufacturers: Diamond Materials GmbH, Diamonex, and Element Six. These devices were investigated using Raman spectroscopy and 6 MV photons from a clinical linear accelerator. Parameters such as the level of the dark (leakage) current and photocurrent, necessary priming dose, linearity of photocurrent with dose rate, and device sensitivity were considered. Device characteristics vary considerably. Devices fabricated using Diamonex material required high priming doses, and displayed high dark currents, low photocurrents (and hence low X-ray sensitivity), and non-linear dose rate responses. In contrast, devices fabricated from Diamond Materials and Element Six material required lower priming doses, and displayed ‘zero’ dark currents (beyond the detection limit), higher photocurrents, and linear dose rate responses. In addition, the Element Six devices exhibited less variation in response when irradiated at different angles of incidence

Prototype X-Ray Detectors Based on CVD Diamond

X-ray detectors have been fabricated from a range of commercially-available chemical vapour deposition (CVD) diamond. They have been packaged and tested in a clinical environment, using clinical apparatus and following clinical procedures: 6 MV linear accelerator, solid water phantom, dosimeter. Some devices exhibited highly desirable characteristics, such as negligible dark currents (sub-pA), low priming doses (few Gy) and high specific sensitivities (up to 586 nC Gy-1 mm-3), demonstrating the potential of these devices as simple-to-use, small size, tissue-equivalent, sensitive x-ray dosimeters. The performance of such devices in clinical applications, such as beam profiling (both depth and off-axis) is currently in progress

Pixel sensitivity variation in a CdTe-Medipix2 detector using poly-energetic x-rays

We have a 1-mm-thick cadmium telluride (CdTe) sensor bump-bonded to a Medipix2 readout chip. This detector has been characterized using a poly-energetic x-ray beam. Open beam images (i.e. without an attenuating specimen between the x-ray source and the detector) have been acquired at room temperature using the MARS-CT system. Profiles of various rows and columns were analyzed for one hundred, 35-ms exposures taken with a bias voltage of -300 V (operating in electron collection mode). A region of increased sensitivity is observed around the edges of the detector. A reasonably periodic, repeatable variation in pixel sensitivity is observed. Some small regions with very low sensitivity and others with zero signals are also observed. Surrounding these regions are circular rings of pixels with higher counts. At higher flux (higher tube current in the x-ray source) there is evidence of saturation of the detector assembly. In this paper we present our understanding of the origin of these features and demonstrate the improved image quality obtained after correcting for these variations