Search Results
Abstract
A model for the rate at which various primary fission products stop in the gas of the source chamber of a gas jet has been constructed. It describes the absorption of fission fragments in Al foils placed between the235U deposit and the gas chamber as well as the penetration of fragments through the gas. The model is based on reported ranges (mean values as a function of A and the dispersion in ranges) and measured activities of Kr and Xe.
Abstract
An extensive study of Mesoamerican obsidian source samples from 37 sites has been begun to better differentiate and define the trace element content at known Mesoamerican obsidian quarries, with particular emphasis on those in Mexico. This paper reports on the first results in that study as well as studies of sample contamination by grinding and results for the new National Bureau of Standards No. 278 Obsidian SRM.
The article presents and describes a manuscript volume which contains some unknown speeches of the famous antitrinitarian thinker, Ernst Soner. Beside the data of the book and the short description of the speeches, the first one is discussed in detail, which is about libertas philosophandi, and emphasizes the importance of criticism and detachment, prefiguring rational thinking. The work is a new proof for the thesis that the rediscovered ancient scepticism was not the only source of early modern rationalism.
Mass spectra of gliclazide drug at various ion sources temperature
Its thermal behavior and molecular orbital calculations
Abstract
Gliclazide (GL, C15H21N3O3S) drug is used as non-insulin-dependant diabetes mellitus. The drug was investigated using thermal analysis (TA) measurements (TG/DTG) and electron impact mass spectral (EI–MS) fragmentation at 70 eV techniques. The mass spectra of GL at different values of ion source temperatures (400, 416, 425, and 440 K) are recorded and investigated. Semiempirical MO calculation, using PM3 procedure, has been carried out on neutral molecule and positively charged species. These calculations included bond length, bond order, bond strain, partial charge distribution, ionization energy, and heats of formation (ΔH f). PM3 procedure provides a basis for fine distinction among sites of initial bond cleavage, which is crucial to the rationalization of subsequent fragmentation of the molecule. The primary fragmentation pathway in both TA and MS (at different values of ion source temperature) is initiated by S–N bond rupture. TA and DTG show one main weight loss at 250.38 °C and four peaks at 271.6, 360.99, 427.93 and 479.17 °C in DTA, which may be attributed to various fragments. Also, the rate constant (K′) of thermal degradation has been tested isothermally at 210 and 600 °C. The calculated rate values are 9.6 × 10−3 and 0.33 × 10−3 s−1, respectively, and discussed. In MS, the effect of ion source temperature on mass spectral fragmentation processes is discussed on the basis of energy considerations using quasi equilibrium theory.
Abstract
To analyze a voluminous radioactive source with the highest possible sensitivity, it is necessary to use both a high efficiency detector and an optimal measurement geometry. The 
optimal
geometry implies positioning the source as close to the detector as possible. It also implies selection of the shape of the source in order to reach the highest efficiency possible (e.g., Marinelli beaker). Under such conditions of measurements, true coincidences may cause systematic errors that can reach levels of more than ten percent for some radionuclides. A method for estimation of the effect of these coincidences was developed. It is based on direct computation of the effect by means of integration of a function which involves the experimentally obtained detection efficiency for the place around the detector. It was found that for the tested detector with a relative efficiency of 15%, the so-called intrinsic peak-to-total calibration may be used in the course of such an integration: It has been shown that theP/T-ratio for the given energy in the working space around the detector may be considered a constant value. Some results from a peak-to-total calibration study in the presence of scattering material are also given.
Abstract
We have collected sixteen total diet samples from two socioeconomic groups in Turkey by duplicate portion techniques. Samples were homogenized with titanium-blade homogenizer, freeze dried and analyzed for their minor and trace elements mostly by neutron activation analysis. Bread and flour samples were also collected from the same regions and analyzed similarly by instrumental neutron activation analysis. We have determined concentrations of more than 25 elements in total diets, bread and flour, and fiber and phytate in total diets. We have determined daily dietary intakes of these population groups, probable source of elements through correlation coefficients, and enrichment factor calculations.
Abstract
The past quarter of a century has seen considerable improvement in time resolution for pulse radiolysis and laser photolysis experiments, made possible by advanced excitation sources. To document the present status, three installations for pulse radiolysis are discussed: a picosecond linac (Tokyo), a nanosecond Van de Graaff (Delft), and a high current accelerator (
ód
). Also indicated are future experimental possibilities, in particular the use of a high current photoemission electron gun. Available lasers for excitation with nanosecond pulses are summarized and a picosecond facility which permits optical and conductivity observations with subnanosecond time resolution is described.
Abstract
A method of99Tc determination has been developed based on sample decomposition followed by purification from interfering elements by hydroxide and oxide precipitations. Technetium is extracted by TBP and electrodeposited onto stainless steel discs from sodium hydroxide solution.99Tcm is used as yield monitor. The method has been applied to study releases from different sources and contents in different samples of atmospheric, terrestrial and marine origin. Results show enhanced99Tc/137Cs activity ratios for samples collected in recent years which are only expected to be contaminated from fallout from nuclear tests. Integrated fallout measurements did not reflect these enhanced ratios.
Abstract
This work describes an in vivo neutron activation analysis facility for small samples, such as rats or human hand, using two 100 
g252Cf neutron sources. The irradiation area is a cylindrical space, of 12 cm diameter and about 15 cm length, with fairly uniform neutron flux distribution. Experimental data on the reproducibility, effects of volume and other conditions for in vivo measurements are given. Comparative atomic absorption data on calcium measurements on rats are reported. The facility is now used for animal experiments as well as human hand irradiations in clinical investigations involving calcium metabolism and bone diseases.
Abstract
The goal of this research is to determine trends and sources of airborne particulates in the centre of Lisbon, by using speciated particulate-matter data and back-trajectory analyses. Results showed that, in 2007, the annual PM2.5 concentration exceeded the World Health Organization recommended levels. PM2.5 diurnal variability and the ratio between weekdays’ and weekends’ concentrations indicated that traffic contributed highly to decreasing air quality. Air back-trajectory analysis showed that maritime air mass transport had a significant role on air quality in Lisbon, promoting the decrease of anthropogenic aerosol concentrations.
