K. W. Jang

Fabrication and performance evaluation of one-dimensional fiber-optic radiation sensor for X-ray profile irradiated by clinical linear accelerator

In this study, one-dimensional fiber-optic radiation sensor with an organic scintillator tip is fabricated to measure high energy X-ray beam profile of CLINAC. According to the energy and field size of X-ray, scintillating light signal from one-dimensional fiber-optic sensor is measured using a photodiode-amplifier system. This sensor has many advantages such as high resolution, real-time measurement and ease calibration over conventional ion chamber and film.

Development of a fibre-optic dosemeter to measure the skin dose and percentage depth dose in the build-up region of therapeutic photon beams

In this study, a fibre-optic dosemeter (FOD) using an organic scintillator with a diameter of 0.5 mm for photon-beam therapy dosimetry was fabricated. The fabricated dosemeter has many advantages, including water equivalence, high spatial resolution, remote sensing and real-time measurement. The scintillating light generated from an organic-dosemeter probe embedded in a solid-water stack phantom is guided to a photomultiplier tube and an electrometer via 20 m of plastic optical fibre. Using this FOD, the skin dose and the percentage depth dose in the build-up region according to the depths of a solid-water stack phantom are measured with 6- and 15-MV photon-beam energies with field sizes of 10 × 10 and 20 × 20 cm(2), respectively. The results are compared with those measured using conventional dosimetry films. It is expected that the proposed FOD can be effectively used in radiotherapy dosimetry for accurate measurement of the skin dose and the depth dose distribution in the build-up region due to its high spatial resolution.

Comparison of the New MOSkin Detector and Fiber Optic Dosimetry System for Radiotherapy

In radiotherapy, interest in real-time dosimetry stems from the desire to monitor the dose delivered to the target volume and the surrounding normal tissue to enable clinicians to track the progress of the treatment, and prevent surrounding tissue from receiving too much radiation dose. In this study, the dosimetric performance of the new MOSkin dosimeter and a Bicron BCF-20 scintillating fiber was compared to depth dose measurements taken with a Farmer-type ionization chamber. The performance of the MOSkin and BCF-20 detectors in the build-up region of the depth dose curve, where the dose gradient is steep, is also compared to readings taken with an Attix chamber. At depths greater than 15 mm, the MOSkin readings deviated from the ion chamber readings by up to 4%, while the fiber optic dosimeter always remained within 3% of the ionization chamber reading. In the build-up region, the MOSkin proved quite capable of measuring the dose at build up when compared to the Attix chamber results, while the fiber optic dosimeter was not able to measure the dose in this region with a high level of precision due to the thick sensitive volume of the scintillating crystal.

Fabrication and Characterization of a Fiber-optic Radiation Sensor for Detection of Tritium

: Ce, and CsI : Tl to select the most effective sensor tip. In addition, we have measured the scintillating lights using a photomultiplier tube as a function of distance between sensor tips to the source with the different activities of hydride tritium. The final results are compared with those which are obtained using a surface activity monitor.

Measurements of longitudinal gamma ray distribution using a multichannel fiber-optic Cerenkov radiation sensor

Cerenkov radiation occurs when charged particles are moving faster than the speed of light in a transparent dielectric medium. In optical fibers, Cerenkov radiation can also be generated due to the fiber?s dielectric components. Accordingly, the radiation-induced light signals can be obtained using the optical fibers without any scintillating material. In this study, we fabricated a multichannel, fiber-optic Cerenkov radiation sensor (FOCRS) system using silica optical fibers (SOFs), plastic optical fibers (POFs), an optical spectrometer, multi-anode photomultiplier tubes (MA-PMTs) and a scanning system to measure the light intensities of Cerenkov radiation induced by gamma rays. To evaluate the fading effects in optical fibers, the spectra of Cerenkov radiation generated in the SOFs and POFs were measured based on the irradiation time by using an optical spectrometer. In addition, we measured the longitudinal distribution of gamma rays emitted from the cylindrical type Co-60 source by using MA-PMTs. The result was also compared with the distribution of the electron flux calculated by using the Monte Carlo N-particle transport code (MCNPX).

Chalcogenide optical fiber based sensor for non-invasive monitoring of respiration

We have fabricated an infrared optical fiber based sensor which can monitor the respiration of a patient. The design of a chalcogenide optical fiber based sensor is suitable for insertion into a high electro-magnetic field environment because the sensor consists of low cost and compact mid-infrared components such as a chalcogenide optical fiber, a filament emitter and a thermopile sensor. A fiber-optic respiration sensor is capable of detecting carbon dioxide (CO2) in exhalation of a patient using the infrared absorption characteristics of carbon gases. It is expected that a mid-infrared fiber-optic respiration sensor, which can be developed based on the results of this study, would be highly suitable for respiration measurements of a patient during the procedure of an MRI.

Feasibility study on the development of respiration sensor using a chalcogenide optical fiber

In this study, we have fabricated an infrared optical fiber based sensor which can monitor the respiration of a patient. The design of a chalcogenide optical fiber based sensor is suitable for insertion into a high electro-magnetic field environment because the sensor consists of low cost and compact mid-infrared components such as an infrared light source, a chalcogenide optical fiber and a thermopile sensor. A fiber-optic respiration sensor is capable of detecting carbon dioxide () in exhalation of a patient using the infrared absorption characteristics of carbon gases. The modulated infrared radiation due to the presence of carbon dioxide is guided to the thermopile sensor via a chalcogenide receiving fiber. It is expected that a mid-infrared fiber-optic respiration sensor which can be developed based on the results of this study would be highly suitable for respiration measurements of a patient during the procedure of an MRI.

Removal of Cerenkov Light in Fiber-optic Radiation Sensor Using Optical Filters

In this study, a miniature fiber-optic radiation sensor has been developed using a water-equivalent organic scintillator for electron beam therapy dosimetry. The intensity of Cerenkov light is measured and characterized as a function of the incident angle of the electron beam from a LINAC. Also, a subtraction method using a background optical fiber without a scintillator and an optical discrimination method using optical filters are investigated to remove Cerenkov light, which could cause problems or limit the accuracy for detecting a fluorescent light signal in a fiber-optic radiation sensor.

Measurements and characterizations of cerenkov light in fiber-optic radiation sensor irradiated by high energy electron beam

In general, Cerenkov light is produced by a charged particle that passes through a medium with a velocity greater than that of visible light. Although the wavelength of Cerenkov light is very broad, the peak is in the almost visible range from 400 to 480 nm. Therefore, it always causes a problem to detect a real light signal that is generated in the scintillator on the fiber-optic sensor tip for dose measurements of high-energy electron beam. The objectives of this study are to measure, characterize and remove Cerenkov light generated in a fiber-optic radiation sensor tip to detect a real light signal from the scintillator. In this study, the intensity of Cerenkov light is measured and characterized as a function of incident angle of electron beam from a LINAC, and as a function of the energy of electron beam. As a measuring device, a photodiode-amplifier system is used, and a subtraction method using a background optical fiber is investigated to remove Cerenkov light.

Characterization of OTDR based fiber-optic humidity sensor

Summary form only given. In this study, the optical time-domain reflectometer (OTDR) based fiber-optic humidity sensor (FOHS) was fabricated to measure humidity in inaccessible hazardous environments. The sensing probe of FOHS consists of a single mode optical fiber and a moisture-sensitive material (mixture of HEC and PVDF) which varies its refractive index according to the relative humidity [1, 2]; here, the end of fiber was coated with the moisture-sensitive material by using the dip coating method. By Fresnel reflection between the sensing material and the single mode fiber, the optical power of the OTDR varies with the relative humidity. To optimize the FOHS, we evaluated the variation of optical power according to the contents (0.23, 0.33, 0.43, 0.53, and 0.63 g) of PVDF in the moisture-sensitive material and wavelengths (1310 and 1550 nm) of the laser source. As the result, the moisture-sensitive material containing 0.43 g of PVDF had the highest sensitivity with 1310nm laser source.