Results 1 - 10 of 1909
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[en] The purpose was to evaluate a commercial silicone diode dosimeter for a patient dosimetry quality assurance program. The diode dosimeter was calibrated against an ion chamber, and percentage depth dose, linearity, anisotrophy, virtual source position, and field size factor studies were performed. Correction factors for lack of full scatter medium in the diode entrance and exit dose measurements were acquired. Dosimetry equations were proposed for calculation of dose delivered at isocenter. Diode dose accuracy and reproducibility were tested on phantom and on four patients. A patient dosimetry quality assurance program based on diode-measured dose was instituted and patient dose data were collected. Diode measured percentage depth dose and field factors agreed to within 3% with those measured with an ion chamber. The diode exhibited less than 1.7% angular dose anisotrophy and less than 0.5% nonlinearity up to 4 Gy. Diode dose measurements in phantom showed that the calculated doses differed from the prescribed dose by less than 1.%; the diode exhibited a daily dose reproducibility of better than 0.2%. On four selected patients, the measured dose reproducibility was 1.5%; the average calculated doses were all within ± 7% of the prescribed doses. For 33 of 40 patients treated with a 6 MW beam, measured doses were within ± 7% of the prescribed doses. For 11 out of 12 patients, a second repeat measurements yielded doses within ± 7% of the prescribed doses. The proposed diode-based patient dosimetry quality assurance program with dose tolerance at ± 7% is simple and feasible. It is capable of detecting certain serious treatment errors such as incorrect daily dose greater than 7%, incorrect wedge use, incorrect photon energy and patient setup errors involving some incorrect source-to-surface-distance vs. source-to-axis-distance treatments. 13 refs., 5 figs., 5 tabs
[en] For personal radiation dose monitoring, electronic personal dosimeters (EPD), also known as active personal dosimeter (APD), using silicon diode detector have the advantage capability of measuring and displaying directly the exposure results of gamma, beta and neutron radiations in real time. They are mainly considered as good complement to passive dosimeters to satisfy ALARA principle in the radiation protection. In this paper, the meansurement methods and algorithms for evaluating personal dose equivalents such as Hp(10) and Hp(0.07) from air-kerma are studied and developed in two directions: the first, named energy correction method based on incident energy determined by the ratio of two detector responses with the different filter configurations; the second new method is carried out in the way that matching the shape of a detector's energy response curve to the kerma-to-personal dose equivalent conversion function provides an approximate means of determining the dose equivalent without the need to resolve the actual incident energies. The algorithm has also been experimentally verified at Secondary Standards Dosimetry Laboratory (SSDL) of Institute for Nuclear Science and Technology by the beam of radiation defined in ISO 4037-1. The obtained results of personal dose equivalents with errors almost less than 30% in energy range from 20 keV to 1.5 MeV are partially met the EPD design requirements according to the IEC 61526 Standard. The work and results of described in this paper are important basics for design and construction of completed electronic personal dosimeter. (author)
[en] In 1931, Wilson applied Block's theory about the energy bands for the motion of electrons in a crystal lattice to semiconductors and showed that conduction can take place in two different ways, by electrons and by holes. Not long afterwards Frenkel showed that these carriers can flow by diffusion in a concentration gradient as well as under the influence of an electric field and wrote down equations for the current flow. The third major contribution, in the late 1930's was the explanation of rectification at a metalsemiconductor contact by Mott and more completely by Schottky. In late 1947 the first transistor of the point contact type was invented by Brattin, Shockley and Bardeen. Then after single crystals of Ge were grown, the junction transistor was developed by the same group. The first silicon transistors appeared in 1954. Then an important step was discovery of the planar transistor by Hoenri in 1960 which led to development of integrated circuits by 1962. Many transistors are produced by batch processing on a slice of silicon. Then in 1965 Mos (Metal-Oxide Semiconductor) transistor and in 1968 LSI (Large Scale Intergration circuits) were developed. Aside from electronic circuits, there are many other applications of semiconductors, including junction power rectifiers, junction luminescence (including lasers), solar batteries, radiation detectors, microwave oscillators and charged-coupled devices for computer memories and devices. One of the latest developments is a microprocessor with thousands of transistors and associated circuitry on a single small chip of silicon. It can be programmed to provide a variety of circuit functions, thus it is not necessary to go through the great expense of LSI's for each desired function, but to use standard microprocessors and program to do the job
[en] To investigate the possibility of replacing conventional Multi Anode Photomultiplier Tubes (MAPMTs) with Silicon Photomultipliers (SiPMs), the 'Silicon Elementary Cell Add-on' (SiECA) is at the moment under development and in its final steps. The aim of SiECA is the detection of UHECRs with SiPMs within the frame of the 'Extreme Universe Space Observatory' (EUSO) pathfinder experiment 'EUSO- Super Pressure Balloon'. In this context, 64 channel SiPM arrays of the newest series manufactured by Hamamatsu have been studied and characterized. The motivation, the idea and the current status of SiECA are presented, and the results of our work on characterizing the newest 64 channel SiPM arrays are discussed. With the focus on these particular studies, the talk also gives a short overview of the status of JEM-EUSO in general and of its other pathfinder studies.
[en] A PIN diode suitable for use as a fast neutron dosimeter, and with greater sensitivity than previous dosimeters, is described. It comprises a long rod or bar of high resistivity silicon with p and n-doped regions at its ends. The mean carrier lifetime within the high resistivity base region is at least 200 microseconds, while the length of the base region is at least three times the mean carrier diffusion length. All the lateral surfaces of the rod are oxidised, so minimizing the rate of carrier recombination at the surface. (author)
[en] ''High flux'' diodes offer advantages over other dosimetric methods in X-ray beams of very high instantaneous intensity: linear accelerators and flash generators. They allow the measurement of pulsed doses and dose rates up to 1010r.s.-1, and give an immediate reading of the dose or peak dose rate by means of simple electronic devices
[fr]Les diodes ''haut flux'' remplacent avantageusement les autres procedes dosimetriques dans les faisceaux de rayons X a tres grande intensite instantanee: accelerateurs lineaires et generateurs flash. Elles permettent la mesure des doses par impulsion et des debits jusqu'a 1010r.s.-1. Elles permettent en outre une lecture immediate de la dose ou du debit crete a l'aide de dispositifs electroniques simples
[en] The application of avalanche photo detectors in various sectors is widely discussed in the last decade. Positive qualities are low power consumption, high efficiency of the registration of photons of impact resistance, and price range. Compact array of avalanche photodiodes are required in a number of devices of medical and scientific destination. Many matrix of silicon diodes are manufactured on a monolithic semiconductor substrate, which are used as general electrode for supplying of voltage to the device. Description of technologies of the creation of new micro pixel in avalanche photodiodes has been presented in this work. Pixel density gives a chance increases the efficiency of the registration of photons.