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211.
R. Britton J. Burnett A. Davies P. H. Regan 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(3):2035-2041
Broad-energy HPGe detectors have a useful range of 3 keV to 3 MeV, making them ideal for the assay of environmental samples. Such measurements however, are hindered by variations in the sample matrix, summing effects, and the Compton continuum. Detectors may be characterised by proprietary software in such a situation, however Monte-Carlo modelling is a useful, inexpensive alternative that also provides greater flexibility when determining the detector response and efficiency during a measurement. In the current work, a full GEANT4 model of a broad-energy HPGe detector is presented, and simulations of various samples are compared to experimental data. These are found to be accurate within 3 % at a confidence level of 95 % for energies from 30 to 3,000 keV, with greater variations below 100 keV due to an increased sensitivity to geometrical inaccuracies. 相似文献
212.
Multidimensional gamma-spectrometry is a powerful technique for making low-level nuclear measurements. The systems typically utilise multiple sodium iodide detectors to measure coincident or anti-coincident gamma-energies. This allows significant background reduction and high selectivity of cascading radionuclides including 22Na. As events are rejected or selected based on their event time, the timing resolution of the multi-channel analyser (MCA) is important. This has been assessed for three compact MCA systems produced by Canberra and Ortec. The Canberra OspreyTM and LynxTM provided the best timing performance, capturing 88.3 and 97.9% of 22Na positron emissions within 200 ns. In comparison only 12.5% of events were measured within 200 ns by the Ortec digiBASE-ETM. However all systems captured the majority of events within 1000 ns, providing multidimensional spectra that allow the evaluation of simultaneous energy combinations. 相似文献
213.
Diti Chatterjee Bhowmick Zhanar Kudaibergenova Lydia Burnett Aleksandar M. Jeremic 《Molecules (Basel, Switzerland)》2022,27(3)
Amyloidosis is a common pathological event in which proteins self-assemble into misfolded soluble and insoluble molecular forms, oligomers and fibrils that are often toxic to cells. Notably, aggregation-prone human islet amyloid polypeptide (hIAPP), or amylin, is a pancreatic hormone linked to islet β-cells demise in diabetics. The unifying mechanism by which amyloid proteins, including hIAPP, aggregate and kill cells is still matter of debate. The pathology of type-2 diabetes mellitus (T2DM) is characterized by extracellular and intracellular accumulation of toxic hIAPP species, soluble oligomers and insoluble fibrils in pancreatic human islets, eventually leading to loss of β-cell mass. This review focuses on molecular, biochemical and cell-biology studies exploring molecular mechanisms of hIAPP synthesis, trafficking and degradation in the pancreas. In addition to hIAPP turnover, the dynamics and the mechanisms of IAPP–membrane interactions; hIAPP aggregation and toxicity in vitro and in situ; and the regulatory role of diabetic factors, such as lipids and cholesterol, in these processes are also discussed. 相似文献
214.
P. N. Finlay Malcolm King A. Burnett 《The Journal of the Operational Research Society》1989,40(2):193-198
One recommended approach to the building of expert systems is to start with a very simple system and to expand the level of detail as the system evolves. With this approach there is the practical problem of organizing the rules as the system develops. This paper describes the use of a folding editor for easing this administrative overhead. 相似文献
215.
H. E. Roberts M. Helba J. J. Carroll J. Burnett T. Drummond J. Lepak R. Propri Z. Zhong F. J. Agee 《Hyperfine Interactions》2002,143(1-4):111-119
Preliminary survey experiments have been performed to examine the triggering of gamma emission from the 31-year Hf-178m2 isomer
using intense monochromatic synchrotron radiation from the X15A beamline at the National Synchrotron Light Source at Brookhaven
National Laboratory. Initial studies were performed to probe incident photon energies over the L
1, L
2, and L
3 X-ray edges of Hf and the 12–13 keV range. Resonances larger than the experimental minimum detectable level of 10−25 cm2 keV were not observed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
216.
Baltrusaitis RM Becker JJ Blaylock GT Brown JS Bunnell KO Burnett TH Cassell RE Coffman D Cook V Coward DH Dado S Dorfan DE Dubois GP Duncan AL Einsweiler KF Eisenstein BI Fabrizio R Gladding G Grancagnolo F Hamilton RP Hauser J Heusch CA Hitlin DG Köpke L Lockman WS Mallik U Mockett PM Mozley RF Nappi A Odian A Partridge R Perrier J Plaetzer SA Richman JD Roehrig JR Russell JJ Sadrozinski HF Scarlatella M Schalk TL Schindler RH Seiden A Simopoulos C Sleeman JC Spadafora AL Stockdale IE 《Physical review letters》1985,55(18):1842-1845
217.
Becker JJ Blaylock GT Bolton T Brown JS Bunnell KO Burnett TH Cassell RE Coffman D Cook V Coward DH Dorfan DE Dubois GP Duncan AL Eigen G Einsweiler KF Eisenstein BI Freese T Gladding G Grancagnolo F Grab C Hamilton RP Hauser J Heusch CA Hitlin DG Köpke L Li A Lockman WS Mallik U Matthews CG Mockett PM Mozley RF Nemati B Odian A Partridge R Perrier J Pitman D Plaetzer SA Richman JD Sadrozinski HF Scarlatella M Schalk TL Schindler RH Seiden A Simopoulos C Spadafora AL Stockdale IE Stockhausen W 《Physical review letters》1987,59(2):186-189
218.
Baltrusaitis RM Becker JJ Blaylock GT Bolton T Brown JS Bunnell KO Burnett TH Cassell RE Coffman D Cook V Coward DH Cui H Dado S Del Papa C Dorfan DE Dubois GP Duncan AL Eigen G Einsweiler KF Eisenstein BI Fabrizio R Favart D Gladding G Grancagnolo F Guy AD Hamilton RP Hauser J Heusch CA Hitlin DG Köpke L Lockman WS Mallik U Matthews CG Mockett PM Moss L Mozley RF Nappi A Nemati B Odian A Partridge R Perrier J Plaetzer SA Richman JD Roehrig J Russell JJ Sadrozinski HF Scarlatella M Schalk TL 《Physical review letters》1986,56(2):107-110
219.
An improved method for determination of (210)Pb, (210)Bi and (210)Po in both natural waters and solid materials has been developed. Polonium-210 is spontaneously plated onto a silver disc from dilute hydrochloric acid medium. Bismuth-210 is then electro-deposited onto a platinum gauze cathode directly from the same solution, with a graphite rod as anode. Finally, (210)Pb is electro-deposited from a fluoroborate medium onto the same platinum gauze, used as the anode. All three nuclides are subsequently measured by standard low-level alpha and beta counting techniques. The speed of this method (approximately 6 hr per sample after pretreatment) is a distinct advantage over existing techniques, as (210)Bi must be quickly separated from (210)Pb because of its 5.02-day half-life. Another advantage of this method is that the chemical form of the sample solution is suitable for use of established separation schemes for determining other decay-series isotopes (U, Th, Pa, etc.) after the three short-lived nuclides have been processed. 相似文献
220.
W. C. Burnett D. R. Corbett M. Schultz E. P. Horwitz R. Chiarizia M. Dietz Anil Thakkar M. Fern 《Journal of Radioanalytical and Nuclear Chemistry》1997,226(1-2):121-127
The analysis of environmental samples for low levels of U, Pu, Am and other actinide elements is often hampered by sample-dependent problems involving the composition and/or mineralogy of specific samples. While relatively small samples (1–2 g of soil or 1–2 of water) are required to reach the extremely low detection limits occasionally mandated for environmental monitoring. One approach to avoid the troublesome and often inexplicable problems collectively referred to as matrix effects is to pre-concentrate actinides into a common form that would then behave uniformly and predictably during a subsequent separation scheme. Recently, a new extraction chromatographic resin based on diphosphonate chemistry was developed at Argonne National Laboratory. This resin commercialized as Eichrom's Actinide Resin, exhibits extremely high affinity for actinide elements even in the presence of high concentrations of salts. We have measured the uptake of actinides by the Dipex® extractant from natural waters and natural matrix soil standards. Water samples have been analyzed for gross -activities and gave results that compared favorably to the traditional approach. In addition, we have obtained good recoveries and excellent separations for soil samples as judged by resolution on the -spectra and the complete absence of interfering energies. 相似文献