Results 1 - 9 of 9
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[en] The total 52V production cross section of elemental chromium has been measured using a DT neutron source and the activation method. Two consecutive determinations of the Cr(n,X)52V cross section gave an average value of 71.4 mb, with a 2.4% estimated error from all sources (+/-1 σ), for neutrons at 14.59 MeV
[en] The total 52V production cross section of elemental chromium has been measured using a deuterium-tritium neutron source and the activation method. Neutrons were produced using a 150-kV Cockroft-Walton accelerator located on a low-scatter grid floor at the center of a large-volume shielded laboratory. Flux normalization was carried out using simultaneous irradiation of iron foils through the induced 56Mn activity. Two consecutive determinations of the Cr(n,X)52V cross section gave an average value of 71.4 mb, with a 2.4% estimated uncertainty (one standard deviation) from all sources. The neutron energy at the O-deg irradiation position was measured using a technique based on neutron-induced reactions in a silicon surface barrier detector. The shift in the position of the α0 peak from (n,α) reactions in 28Si as the detector was moved from 96 to 0 deg was used to deduce the neutron energy from its known value of 14.02 MeV at 96 deg. The mean neutron energy obtained was 14.59 +/- 0.02 MeV, with a spread in energy across the irradiation sample of about 0.30 MeV. The paper summarizes the contribution of various steps in the cross-section measurement to the overall uncertainty. The major contributors include uncertainties arising in the absolute calibration of the counting efficiency of the flow proportional counter, and the uncertainty in the reference cross section used to determine the absolute neutron flux
[en] Full text: Ambient radiation levels at the patient waiting areas have been greatly reduced after remodeling of our Nuclear Medicine Department (NMD) based on the ALARA consideration. Complete ambient radiation monitoring of our NMD before remodeling had been characterized and published earlier by the same authors elsewhere. The NMD outpatients, with an initial dose of up to 740 MBq (20 mCi) per case, may wait around and incidentally congest in one place that could cause an unexpected higher exposure level in public access areas. In this new surveillance study after remodeling, the ambient radiation time-profile, peak dose rates and daily doses have been re-evaluated by using high sensitivity, digital survey dosimeters. As a preliminary result, with our newly improved facility in operation, we have demonstrated the NMD waiting room average daily dose has dropped from about 3.0 μSv to 0.42 μSv during most of busy days in comparison. The hourly peak dose rate detected in patient waiting areas has also reduced to a factor of more than two, from maximum dose rate of 40.4 μSv/h to 15.4 μSv/h, during one worst case scenario. The great reduction of the environment dose was achieved mainly by using larger room space with thicker lead wall, from previous 2-mm to new 5-mm in lead thickness, and by increasing patient waiting rooms/areas with less chairs available in each seating location. Other NMD administrative control measure of our dose reduction program has also been emphasized in better patient routing, scheduling and less waiting time for the diagnostic patients. (author)
[en] This paper reports on a post-accident wide-range gaseous effluent radiation monitoring system (WRGERMS) that was calibrated over a seven-decade range of radioactive gas concentration for its mid-range and high-range response detectors. A large quantity of Xe-133 calibration gas was used in a specially designed gas-handling cart to perform the calibration prior to installation of the monitor at the reactor site. Using the principle of cryogenic adsorption, the gas-handling cart manipulated the concentration of the Xe-133 gas from a high of 1.7 x 105 μCi/cc to a low of 0.01 μCi/cc. Energy dependence of the WRGERMS detectors was also tested using Xe-133 and Cs-137 sources. The monitor's response to a set of transfer sources was established to permit periodic performance testing and subsequent detector replacement without performing complete X-133 gas calibrations
[en] Full text: Short-term environment dose-rate assessments using real-time digital dosimeters within a Nuclear Medicine Department (NMD) are gaining more world-wide uses recently. In the past, conventional ion chamber-type survey-meters are used dominantly in environmental dose rates evaluation. Although it has suffered less gamma energy-dependency, but it is less sensitive in comparison with other digital dosimeters and more bulky in design that can hardly make it into a pocket size application. With modern electronic advancement and its shrinking in physical size, real-time personal dosimeter nowadays has gaining more popular to use a miniature G-M counter or a solid-state diode sensor, or even a NaI(Tl) scintillation device for ambient radiation monitoring. Radiation sensor operated in pulse-mode can never been used in doses or dose rates determination since each digital pulse has carried no energy information of the impinging gamma ray being interactive with, especially in the G-M counter or the diode sensor case. The raw count rates measured from a pulse-mode device are heavily dependent on the packaging of the sensor to make it less energy-sensitive. The doses or dose rates are then calculated by using a built-in conversion factor, based on a Cs-137 beam source calibration data conducted by various manufacturing vendors, to convert its raw counts into a so-called dose or dose-rate unit. In this study, we have focused our interests in the low energy response of the digital dosimeters from several brands currently for our in-house uses. Mainly, Tc-99m and I-131 in point sources and water phantoms detection configurations have been deployed to simulate our NMD outpatients for environment radiation monitoring purpose. The energy-dependent correction factors of the digital dosimeters will be evaluated by using calibrated Tc-99m or I-131 standard sources directly that has much lower gamma energy than the Cs-137 beam source of 661 keV. In the near future, we would extend this study to include the I-125 sources, with gamma energy of 35 keV, that have also been used routinely in our hospital. As a preliminary result of this on-going research project, we have found that the NaI(Tl) hand-held dosimeter has grossly over-estimated in the low energy dose response. The G-M counters are more energy-dependant in point source or beam source calibration. For environment radiation monitoring concern within our NMD, we found the energy-compensated G-M counter suffered the least in energy-dependency during water phantom calibration testing. (author)
[en] Full text of publication follows: Potential environmental dose rates in a patient waiting room at the PET/CT Imaging Center within our Nuclear Medicine Department (N.M.D.) are evaluated by both of the computer modeling method and real-time monitoring in practical settings. The maximum dose rate is directly read from a peak dose-rate frozen-up, digital gamma G-M survey meter. The design basis of our PET/CT Imaging Center facility has assumed a maximum total of five 18 FDG-patients presented at any given time either in an Am or a Pm session according to two separated drug batch delivering runs. Due to the relatively high gamma energy of 511 keV emitted by the F- 18 labeled compound, we have remodeled our facility with a 0.5-cm thick Pb wall and larger space separations between rooms that include a PET/CT scan room, two separated 18 FDG i.v. injection rooms, and a delayed-phase patient waiting room. Patient could normally complete two separate PET/CT scan runs, if a delayed-phase scan is needed, within three hours time frame from an initial dose of 370 MBq (10 mCi) that has a physical half-live of 110 minutes for an F-18 labeled compound. When all the needed scans are finished, the patient is released from our PET/CT Imaging Center that has to follow the radiation safety guideline of less than 50 mSv/hr (5 m R/hr) at one meter distance. During typical operation, each drug i.v. injection room or the scan room is restricted to one patient access only. As a worst case scenario, the maximum ambient dose rate may only occur when two or more delayed phase patients would stay in the PET/CT waiting room that is excluded for other non-PET patient use. Theoretically using a computer discrete-ordinate integrating methods, dose rates at one meter distance from a mid-point geometry, based on a simulated 10 mCi F-18 point, line or volumetric source (assuming 170 cm in height and 20 cm in radius of homogeneous water media), can also be calculated to give values of 5.71, 4.73 and 3.39 m R/hr, respectively. For preliminary results, vendor-supply calibrated point sources have been performed at one meter distance to yield an averaged value of 0.74 +/ - 0.03 m R/hr per mCi 18 FDG. Directly measured ambient dose rates from individual patient showed large variations depending on the 18 FDG initial dose administered and patient metabolism that some F-18 are expelled from body due to urinations during course of the scans. By chance since our PET/CT Imaging Center started in August, 2005, we had encountered only once that a practical situation in which potential maximum ambient radiation dose rate did occur to give a value of 84.7 mSv/hr (8.47 m R/hr) when two delayed phase patients (about 2 hours delaying after drug administered) sat next to each others on a waiting room sofa chair for three people. More measurement data will be compiled if we could receive more on-going patients to assess if further administration controls or facility improvements are necessary as radiation safety ALARA concerns. (authors)
[en] A post-accident wide-range gaseous effluent radiation monitor system (WRGERMS) was calibrated over a seven-decade concentration range. Reliable, safe handling and control of the radioactive xenon-133 calibration gas was achieved through the use of a gas-handling cart which applied the principle of cryogenic absorption to manipulate the concentration of the calibration gas over the calibration range covered. A single 130 Ci sample of xenon-133 gas was used to provide calibration data over the range of 0.01 μCi/cc to 7.7E+5 μCi/cc. The calibration was performed without significant personnel radiation dose and with no release of xenon-133 to the environment. Data obtained were traceable to the National Bureau of Standards and fully met the requirements of USNRC Regulatory Guides 1.97 and 4.15. Monitor response was also documented with NBS-traceable transfer sources. The energy-dependence of the monitor detector assembly was investigated and found to be essentially independent of gamma-ray photon energy at 81 and 662 keV
[en] Four Taiwanese native Miscanthus floridulus lines, collected at altitudes of 260, 500, 1000, and 1500 m were cultivated in 2009 and 2010. The plant height and tiller numbers of four M. floridulus lines increased gradually along with the growing time. These M. floridulus lines had the tallest plant height and most tiller number after these species were planted 210 days. Line 3, which was collected at the altitude of 1000 m, had the ability to grow at low temperature. Line 3 M. floridulus had the highest plant height, tiller number, fresh and dry yields than other three lines. Fresh and dry yields of Line 3 were positively correlated to the plant height, tiller number, and leaf width, but showed no correlation with the leaf length. The correlation between agronomic traits and climatic data was also studied. Results can be used as a model for developing a non-food crop-based energy production system in the future. -- Highlights: → Miscanthus floridulus collected at 1000 m altitude had the highest plant height, tiller number, fresh and dry yields. → Fresh and dry yields of were positively correlated to the plant height, tiller number, and leaf width. → Fresh and dry yields showed no correlation with the leaf length. → The accumulative rainfall, temperature, radiation, and exposure time to radiation were positively correlated to the plant height, leaf length and leaf width.
[en] The simultaneous existence of magnetic and ferroelectric ordering is a characteristic of multiferroic materials. The search for new multiferroics is partly motivated by the need for non-volatile random access memories for which the electric polarisation (magnetisation) is controlled by magnetic field (electric field) or vice versa. The use of such materials would be extremely beneficial for the next generation of electronic devices (mobile phones, tablets etc) whereby compact size constraints are important as well as optimising reading/writing speeds and power consumption. YBaCuFeO5 has been classified as a type-II multiferroic due to its complex magnetic interactions and low temperature feroelectricity. Two magnetic phase transitions of antiferromagnetic nature have been found near TN1 = 450 K and TN2 = 170 K. The first represents the ordering of the Fe3+ ions into a commensurate antiferromagnetic state, while the second represents the ordering of the Cu2+ ions giving an overall incommensurate antiferromagnetic ground state. For the first time, using modified traveling solvent floating zone growth method, we have been able to grow a centimeter-sized, high-quality, singlecrystal of YBaCuFeO5. Magnetisation and neutron diffraction results indicate a complex magnetic phase diagram in this material with a strong hysteresis effect and a chiral magnetic ground state.