A New Type of Cylindrical a-Si:H X-Ray Detector
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Deposition
Radioactive source
Hydrogenerated amorphous silicon is usually prepared by decomposition of silane at low temperature T < 400°C in a glow discharge environment. Recently we have explored a novel process involving thermal decomposition of silane around 600°C followed by post-hydrogenation in a hydrogen plasma. The physical properties of this type of film are discussed and compared to those of films prepared in the usual way.
Glow discharge
Silanes
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Recent advances in radiation therapy have made obvious the need for dosimeters that can measure three-dimensional (3-D) dose distributions. Currently, radiosensitive gel dosimeters have provided 3-D dose measurements using the MRI technique. However, this method has some limitations. Recently, a novel transparent polymer dosimeter, PRESAGE, has been introduced which exhibits a radiochromic response when exposed to ionizing radiation. This dosimetry technique has some advantages compared with other gel dosimeters. In this study, the dose response, linearity, sensitivity, and stability of this type of dosimeter were investigated for different levels of the activator, and leuco dye concentration. In this regard, the PRESAGE dosimeters were made with different formulations and were irradiated by gamma-rays of Cobalt-60 in the dose range of 0-50 Gy. Then, the optical absorption changes of the dosimeters were measured by a spectrophotometer over a period of 14 days after the irradiation. The results indicated that increasing the activator concentration leads to the increase of the sensitivity, but decreases the stability of the dosimeter response. Furthermore, it was noted that the dosimeter shows a linear response to the radiation dose with a high level of correlation (R 2 >0.99).
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Purpose The aims of this study were to develop a flexible film dosimeter applicable to the irregular surface of a patient for in vivo dosimetry and to evaluate the device’s dosimetric characteristics. Methods A flexible film dosimeter with active layers consisting of radiochromic‐sensitive films and flexible silicone materials was constructed. The dose‐response, sensitivity, scanning orientation dependence, energy dependence, and dose rate dependence of the flexible film dosimeter were tested. Irradiated dosimeters were scanned 24 h post‐irradiation, and the region of interest was 5 mm × 5 mm. Biological stability tests ensured the safety of application of the flexible film dosimeter for patients. A preliminary clinical study with the flexible film dosimeter was implemented on four patients. Results The red channel demonstrated the highest sensitivity among all channels, and the response sensitivity of the dosimeter decreased with the applied dose, which were the same as the characteristics of GAFCHROMIC EBT3 radiochromic films. The flexible film dosimeter showed no significant energy dependence for photon beams of 6 MV, 6 MV flattening filter‐free (FFF), 10 MV, and 15 MV. The flexible film dosimeter showed no substantial dose rate dependence with 6 or 6 MV FFF. In terms of biological stability, the flexible film dosimeter demonstrated no cytotoxicity, no irritation, and no skin sensitization. In the preliminary clinical study, the dose differences between the measurements with the flexible film dosimeter and calculations with the treatment planning system ranged from −0.1% to 1.2% for all patients. Conclusions The dosimeter developed in this study is a flexible film capable of attachment to a curved skin surface. The biological test results indicate the stability of the flexible film dosimeter. The preliminary clinical study showed that the flexible film dosimeter can be successfully applied as an in vivo dosimeter.
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The current study was performed to investigate the influence of high temperature on the value of radiation dose measured by optically stimulated liminescence (OSL) dosimeter or radio photo luminescence (RPL) dosimeter (glass dosimeter) . Serial measurements of temperature in the car confirmed that it can rise to 80°C or higher in the area irradiated with sun beam. The relationship between the temperature and the radio dose measured by X-ray irradiated OSL dosimeter or glass dosimeter under the condition from 50°C to 90°C after the set of 3h. to 72h.The value measured by OSL dosimeter tended to be lower with higher temperature or longer setting time. On the other hand, those factors did not influence the value measured by glass dosimeter.
Optically stimulated luminescence
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Radiation dosimetry has the purpose of quantifying the dose received by the occupationally exposed individual. The device used in this process is called a dosimeter, the dosimeter can be used in different situations, for example, the dosimeter used to quantify the dose received in the fingers is the ring model dosimeter, for the extremity, which is the focus of this work. In Brazil, we still do not have standards for the calibration of extremity dosimeters, therefore, in this work, the CASEC recommendations were used, adapted for extremity dosimetry. For a dosimeter to be used in its respective routine, it must present results within some pre-established limits in reference standards. For this purpose, energy dependence and angular dependence tests were carried out. To calibrate the LiF:Mg,Ti thermoluminescent dosimeters, a phantom rod was used. The phantom rod has the function of simulating the region of interest, in the case of this work, the fingers. The dosimeters were irradiated in the magnitude Hp(0.07), with the doses and energies recommended by the CASEC standard. The aim of this work is to characterize end dosimeters in the ring model with LiF:Mg,Ti detectors.
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Fields that use non-destructive testing (NDT) invest significant amounts of time and resources toward building a radioactive source monitoring system, for preventing any potential radiation-related accidents. However, various elements that can cause potential radiation accidents due to silicon-based photodiodes are involved. Therefore, research on new materials that can effectively detect high-energy gamma ray is necessary. This study focused on developing a new dosimeter material for a real-time monitoring system that can detect the location of a radioactive source. It was confirmed that the fabricated HgI 2 dosimeters have sufficient reproducibility and dose linearity for gamma rays. Based on these results, the HgI 2 dosimeter was verified to satisfy the general requirements of NDT source-monitoring systems. These monitoring systems are expected to be easily operable by workers and prevent potential radiation accidents.
Radiation monitoring
Radioactive source
Benchmark (surveying)
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In a previous study, we reported on a novel (prototype) real-time patient dosimeter with non-toxic phosphor sensors. In this study, we developed new types of sensors that were smaller than in the previous prototype, and clarified the clinical feasibility of our newly proposed dosimeter. Patient dose measurements obtained with the newly proposed real-time dosimeter were compared with measurements obtained using a calibrated radiophotoluminescence glass reference dosimeter (RPLD). The reference dosimeters were set at almost the same positions as the new real-time dosimeter sensors. We found excellent correlations between the reference RPLD measurements and those obtained using our new real-time dosimeter (r2 = 0.967). However, the new type of dosimeter was found to underestimate radiation skin dose measurements when compared with an RPLD. The most probable reason for this was the size reduction in the phosphor sensor of the new type of dosimeter. We believe that, as a result of reducing the phosphor sensor size, the backscattered X-ray irradiation was underestimated. However, the new dosimeter can accurately determine the absorbed dose by correcting the measured value with calibration factors. The calibration factor for the new type dosimeter was determined (by linear regression) to be ~1.15. New real-time patient dosimeter design would be an effective tool for the real-time measurement of patient skin doses during interventional radiology treatments.
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Silicon PIN diodes with an active area of 1 cm × 1 cm were fabricated on a high resistivity, (100)-oriented, n-type, 380-μm thick and 5-inch silicon wafer. These diodes were originally fabricated on purpose to monitor strip sensor fabrication processes. To evaluate the performance of the silicon PIN diode, we measured the signal-to-noise ratio (SNR) and energy resolution using radioactive sources. We measured the radiation detection responses of the silicon PIN diodes and observed photopeaks from radioactive sources, Am-241, Sr-90 and Cs-137. The spectrum by simulation was compared with those of the source tests to understand the measurement results. The tests with Am-241 and Cs-137 sources used random trigger because γ fully deposits its energy in a silicon PIN diode. Another PIN diode was used for trigger purpose with Sr-90, β source. Am-241 test showed a sharp peak of 59.5 keV γ as we expected. The γ peak was used for calibration that converts ADC value into energy. We used Cs-137 source to compare a resolution at the lower energy level (32 keV γ) with 59.5 keV γ. Two different conditions were set for Cs-137; without a lead-block and with 3mm-lead-block to reduce β background. In the test of Sr-90, the SNR of the silicon PIN diode was measured to be 36.0. We present the energy resolution and the SNR of the diode measured by using the radioactive sources.
PIN diode
Radioactive source
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We describe measurements on a-Si films made by adding atomic hydrogen during evaporation of silicon. The material has conductivity comparable to that formed by silane decomposition and is also photoconducting. The photocurrent in these initial experiments is smaller than in the bes silane-produced films.
Photoconductivity
Photocurrent
Silanes
Nanocrystalline silicon
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Experimental Calibrations of a Silicon Rectifier Developed as a Fast Neutron Sub-Miniature Dosimeter
We can readily., summarize the significant points that have been elicited from these experiments. 1. The response of this type of dosimeter is fundamentally reproducible. It is felt that increased uniformity can be achieved by further optimization and control of the processing techniques. 2. The dosimeter can be given the desired, almost linear, sensitivity in the biological dose range of interest by selection of an appropriate base width (somewhere between 40 and 60 mils). 3. The response of the dosimeter is independent of the delivery rate of the neutron flux, up to a rate of at least 107 rads per second. 4. The dosimeter essentially does not respond to gamma radiation in the energr and dose ranges of interest. 5. The response of the dosimeter is essentially independent of its orientation with respect to the direction of the incident neutron flux. U. The dosimeter is subject to a significant amount (from 10 to 20 per cent) of room temperature anneal during the first few days after initial exposure. 7. The sensitivity of an exposed dosimeter changes when the device is anmealed at elevated temperatures. 8. The response of the dosimeter appears to be dependent on the energies of the incident neutrons. Some of these points refer to desirable features of the fast neutron dosimeter. The und-ersirable features, we feel, can be remedied or accounted for through further research and development efforts.
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