The Experts below are selected from a list of 877323 Experts worldwide ranked by ideXlab platform
W Yi - One of the best experts on this subject based on the ideXlab platform.
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aluminum 26 Sodium 22 and cobalt 60 in two drill cores and some other samples of the jilin chondrite
Meteoritics & Planetary Science, 1996Co-Authors: G Heusser, Z Ouyang, Jurgen Oehm, W YiAbstract:— Two drill cores have been taken from the main mass of the Jilin chondrite, Jilin I. One was bored perpendicular to the 2π surface of the first exposure stage, the other parallel to this surface, and both intersected at the presumed 4π center of Jilin's second exposure stage. The probed depths were 65 cm and 105 cm, respectively, with a diameter of 26.5 mm. Fifteen drill core samples, 2 documented samples and 14 strewn field samples have been analysed for 26Al, 60Co and 22Na. The reconstruction of the preatmospheric Jilin via60Co resulted in slight deviations for the center position and for the radius (now R = 80+10−5 cm) compared to an earlier study in 1985. The 60Co production rate profile is now almost completely reproduced. A constant production rate of 22Na and of 26Al during the 4π irradiation is confirmed also for the center region. The good linear correlation of 26Al and 21Ne yields slightly revised irradiation ages for both stages of t1 = 7 ± 1 Ma and t2 = 0.32+0.06-0.03 Ma.
K J Thomas - One of the best experts on this subject based on the ideXlab platform.
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simplified method for the in situ collection and laboratory analysis of cosmogenic tracers sulfur 35 and Sodium 22 to determine residence time distributions and water ages
Analytical Chemistry, 2021Co-Authors: A. Deinhart, Melissa Thaw, Richard K. Bibby, A Visser, K J ThomasAbstract:The use of cosmogenically produced sulfur-35 (T1/2 = 87 days) and Sodium-22 (T1/2 = 2.6 years) as intrinsic tracers can provide valuable information on catchment hydrology, flow paths, and subsurface storage. A new and straightforward method was created to determine the activities of both 35S and 22Na in various water sources by pumping large volumes (up to 1000 L) of water through cation- and anion-exchange resin columns in the field to collect Sodium and sulfate ions and simple chemistry in the lab. Samples are counted for 35S using liquid scintillation counting (LSC) and for 22Na via γ spectroscopy. Our novel in situ method provides faster sample throughput as well as better counting statistics and lower detection limits. Both methods were successfully applied at the Southern Sierra Critical Zone Observatory.
Macías Montero, José Gabriel - One of the best experts on this subject based on the ideXlab platform.
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VIPPIX: A readout ASIC for the next generation of human brain PET scanners
'Edicions de la Universitat de Barcelona', 2018Co-Authors: Macías Montero, José GabrielAbstract:Positron emission tomography (PET) is a molecular imaging technique used for several decades in nuclear medicine that provides precise physiological information of the human body, what is crucial in oncology, cardiology, and neuropsychiatry. Due to physical, the best spatial resolution of PET is approximately 1 mm for human brain scanners. Unfortunately, the minimum resolution of the best commercial PET scanners for humans is 4-5 mm due to technological limitations. In this thesis, an application specific integrated circuit (ASIC) to readout the energy and the time stamp of a high-density and highly-granulated Cadmium Telluride detector for a novel PET scanner design is presented. The research presented here was realized within the framework of Voxel Imaging PET pathfinder ERC project to develop detector modules for positron emission tomography applications and reach their actual physical limits. The VIP PET scanner is based on the stacking of 2-mm thickness pixelated hybrid detectors. Every CdTe detector is pixelated into an array of 10 x 10 voxels of 1 mm x 1 mm x 2 mm size and is connected to a pixelated ASIC to readout independently the energy and the time stamp of every photon interaction. The VIP PET is based on more than 6 million voxels with independent energy and timing readout to reach the physical limits of PET. The simulated performance based on the properties of CdTe detectors shows a scatter fraction of approximately 4 % due to an excellent energy resolution of 1.6 % FWHM of the CdTe detectors. By simulation, the VIP PET is able to distinguish 1 mm size radioactive point-like source. The characterization of 2-mm thickness CdTe detectors using commercially available single-channel readout electronics is reported. Using a Sodium-22 radioactive source, the 511 keV photopeak resolution and the coincidence time resolution of back-to-back photons were measured with – 1000 V/mm detector bias voltage at -8 Celsius degree. An energy resolution of 1.6 % FWHM and a time coincidence resolution of 6 ns FWHM were obtained for photoelectric interactions. The architecture of the VIPPIX ASIC, i.e. the ASIC developed for VIP project, is based on an array of 10 x 10 independent pixel electronics controlled by a global controller and a common time to digital converter (TDC). Additional voltage and current references are generated in the ASIC’s back-end with a temperature sensor and a chip-ID cell. Every pixel electronics composes of a programmable gain preamplifier with detector’s leakage dynamic compensation, a tuneable peak-time pulse shaper connected to a peak-and-detect circuit, a 10-bit analog-to- digital converter (ADC), a pulse discriminator with adjustable offset, and a local pixel digital controller. The measured equivalent noise charge (ENC) of the pixel is 150 e- RMS and the trigger time jitter is approximately 1 ns for energy depositions larger than 200 keV. The time resolution of the integrated TDC is 600 ps FWHM. Twelve wafers of VIPPIX ASIC has been fabricated and characterized. Best quality ASICs have been mounted on 720 CdTe detectors and stacked in 18 detector modules with 40 hybrid detectors each to build the VIP PET prototype. Five modules have been characterized with a Sodium-22 radioactive source. The performance of approximately 18000 pixels shows a resolution of 2.2 % FWHM and a coincidence time resolution of 60 ns FWHM for 511 keV photopeak at -250 V/mm detector bias. Therefore, the main goal of the research has been accomplished. A new PET design based on pixelated Cadmium Telluride detectors using dedicated readout ASICs has been successfully fabricated, partly characterized, and is ready for image acquisition
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VIPPIX: A readout ASIC for the next generation of human brain PET scanners
'Edicions de la Universitat de Barcelona', 2018Co-Authors: Macías Montero, José GabrielAbstract:[eng] Positron emission tomography (PET) is a molecular imaging technique used for several decades in nuclear medicine that provides precise physiological information of the human body, what is crucial in oncology, cardiology, and neuropsychiatry. Due to physical, the best spatial resolution of PET is approximately 1 mm for human brain scanners. Unfortunately, the minimum resolution of the best commercial PET scanners for humans is 4-5 mm due to technological limitations. In this thesis, an application specific integrated circuit (ASIC) to readout the energy and the time stamp of a high-density and highly-granulated Cadmium Telluride detector for a novel PET scanner design is presented. The research presented here was realized within the framework of Voxel Imaging PET pathfinder ERC project to develop detector modules for positron emission tomography applications and reach their actual physical limits. The VIP PET scanner is based on the stacking of 2-mm thickness pixelated hybrid detectors. Every CdTe detector is pixelated into an array of 10 x 10 voxels of 1 mm x 1 mm x 2 mm size and is connected to a pixelated ASIC to readout independently the energy and the time stamp of every photon interaction. The VIP PET is based on more than 6 million voxels with independent energy and timing readout to reach the physical limits of PET. The simulated performance based on the properties of CdTe detectors shows a scatter fraction of approximately 4 % due to an excellent energy resolution of 1.6 % FWHM of the CdTe detectors. By simulation, the VIP PET is able to distinguish 1 mm size radioactive point-like source. The characterization of 2-mm thickness CdTe detectors using commercially available single-channel readout electronics is reported. Using a Sodium-22 radioactive source, the 511 keV photopeak resolution and the coincidence time resolution of back-to-back photons were measured with – 1000 V/mm detector bias voltage at -8 Celsius degree. An energy resolution of 1.6 % FWHM and a time coincidence resolution of 6 ns FWHM were obtained for photoelectric interactions. The architecture of the VIPPIX ASIC, i.e. the ASIC developed for VIP project, is based on an array of 10 x 10 independent pixel electronics controlled by a global controller and a common time to digital converter (TDC). Additional voltage and current references are generated in the ASIC’s back-end with a temperature sensor and a chip-ID cell. Every pixel electronics composes of a programmable gain preamplifier with detector’s leakage dynamic compensation, a tuneable peak-time pulse shaper connected to a peak-and-detect circuit, a 10-bit analog-to- digital converter (ADC), a pulse discriminator with adjustable offset, and a local pixel digital controller. The measured equivalent noise charge (ENC) of the pixel is 150 e- RMS and the trigger time jitter is approximately 1 ns for energy depositions larger than 200 keV. The time resolution of the integrated TDC is 600 ps FWHM. Twelve wafers of VIPPIX ASIC has been fabricated and characterized. Best quality ASICs have been mounted on 720 CdTe detectors and stacked in 18 detector modules with 40 hybrid detectors each to build the VIP PET prototype. Five modules have been characterized with a Sodium-22 radioactive source. The performance of approximately 18000 pixels shows a resolution of 2.2 % FWHM and a coincidence time resolution of 60 ns FWHM for 511 keV photopeak at -250 V/mm detector bias. Therefore, the main goal of the research has been accomplished. A new PET design based on pixelated Cadmium Telluride detectors using dedicated readout ASICs has been successfully fabricated, partly characterized, and is ready for image acquisition
G Heusser - One of the best experts on this subject based on the ideXlab platform.
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aluminum 26 Sodium 22 and cobalt 60 in two drill cores and some other samples of the jilin chondrite
Meteoritics & Planetary Science, 1996Co-Authors: G Heusser, Z Ouyang, Jurgen Oehm, W YiAbstract:— Two drill cores have been taken from the main mass of the Jilin chondrite, Jilin I. One was bored perpendicular to the 2π surface of the first exposure stage, the other parallel to this surface, and both intersected at the presumed 4π center of Jilin's second exposure stage. The probed depths were 65 cm and 105 cm, respectively, with a diameter of 26.5 mm. Fifteen drill core samples, 2 documented samples and 14 strewn field samples have been analysed for 26Al, 60Co and 22Na. The reconstruction of the preatmospheric Jilin via60Co resulted in slight deviations for the center position and for the radius (now R = 80+10−5 cm) compared to an earlier study in 1985. The 60Co production rate profile is now almost completely reproduced. A constant production rate of 22Na and of 26Al during the 4π irradiation is confirmed also for the center region. The good linear correlation of 26Al and 21Ne yields slightly revised irradiation ages for both stages of t1 = 7 ± 1 Ma and t2 = 0.32+0.06-0.03 Ma.
Keith Newgrain - One of the best experts on this subject based on the ideXlab platform.
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efficacy of the tritiated water and 22na turnover methods in estimating food and energy intake by emperor penguins aptenodytes forsteri
Physiological and Biochemical Zoology, 1992Co-Authors: Graham Robertson, Keith NewgrainAbstract:The accuracy of the tritiated water (HTO) and Sodium-22 ($^{22}Na$) turnover methods as estimators of dietary water and Sodium intake was evaluated in emperor penguins fed separate diets of squid and fish. Emperor penguins assimilated 76.2% and 81.8% of available energy in the squid and fish diets, respectively. Both isotopes had equilibrated with body water and exchangeable Sodium pools by 2 h after intramuscular injection. The tritium method yielded reliable results after blood isotope levels had declined by 35%. On average the tritium method underestimated water intake by 2.9%, with a range of-10.3% to + 11.1%. The $^{22}Na$ method underestimated Na intake on average by 15.9% with the errors among individuals ranging from -37.2% to -1.8%. Discrepancies with $^{22}Na$ turnover were sign ficantly greater with the squid diet than the fish diet. The results confirm the reliability of the tritium method as an estimator of food consumption by free-living emperor penguins (provided seawater and freshwater ing...