Scholarly Publications - Chemistry

Permanent URI for this collectionhttps://hdl.handle.net/11693/115489

Browse

Now showing 1 - 20 of 739

Open Access
Sedimentation rates in the central lake constance determined with210Pb and137Cs
(Birkhäuser-Verlag, 1987) von Gunten, H. R.; Sturm, M.; Erten, H. N.; Rössler, E.; Wegmüller, F.
Sediment cores from central Lake Constance were dated with210Pb and137Cs. A sedimentation rate of (0.11±0.02) g·cm-2·y-1 was determined with the210Pb method.137Cs measurements revealed sedimentation rates of (0.11±0.01) g·cm-2·y-1 and (0.08±0.01) g·cm-2·y-1 respectively for two different cores sampled at the same location. The lower Cs-dated value indicates incomplete core recovery and demonstrates the sensitivity of this simple dating method to small losses of material at the water/sediment interface. An unambiguous application of the137Cs method is, therefore, only possible if complete core recovery is ensured. Sedimentation rates based on particulate matter, collected in sediment traps at various water depths, agree with the results of the radioisotope methods. Estimates of 30-125 days residence times for suspended particulate matter were calculated from7Be measurements. © 1987 Birkhäuser Verlag.
Open Access
Sorption/desorption of Cs on clay and soil fractions from various regions of Turkey
(Elsevier, 1988) Erten, H. N.; Aksoyoglu, S.; Göktürk, H.
The sorption desorption behaviour of Cs ion in the concentration region of 10−8 to 10−4 meqml−1 have been studied using clay and soil fractions from various regions of Turkey. The sorption curves for all the material studied show similar behaviour indicating at least two different sorption processes. One with high and the other with low distribution coefficients. The results of desorption studies indicate that Cs cation is to a large extent attached to the solid material in a reversible manner. The adsorption isotherms were found to be nonlinear in all cases. The increase og RD values with decreasing particle size in most cases, suggests that sorption and or exchange is primarily a surface phenomenon in the clay and soil fractions studied.
Open Access
Efficiency calibration and summation effects in gamma-ray spectrometry
(Kluwer Academic Publishers, 1988) Erten, H. N.; Aksoyoğlu, S.; Göktürk, H.
Precise, absolute γ-ray efficiences (∈γ) and total efficiences (∈T), have been measured at various distances from the detector, using a set of standards. The observed linear variation of ∈γ and ∈T as well as ∈γ/∈T with Eγ and {Mathematical expression} provides a simple means of interpolation and extrapolation. Experimental coincidence summation effects were determined for various nuclides and compared with calculated values. The results are found to be in good agreement with each other. © 1988 Akadémiai Kiadó.
Open Access
Sorption of cesium and strontium on montmorillonite and kaolinite
(De Gruyter Oldenbourg, 1988) Erten, H. N.; Aksoyoglu, S.; Hatipoglu, S.; Göktürk, H.
Sorption characteristics of Cs+ and Sr++on montmorillonite and kaolinite type clays and soil fractions from various regions of Turkey were studied using the batch method. 137Cs and 90Sr were used as tracers. Concentrations of Cs+ and Sr++ ions ranged from 10-8to 10-2 mol/1; natural groundwater was used and the grain size of the solid particles was < 20 yμm. Equilibrium was reached in 4 - 7 days for Cs+and 7 - 11 days for Sr++. The distribution coefficient, RD, increased with decreasing grain size, suggesting mainly a surface phenomenon. The sorption isotherms were non-linear suggesting at least two different sorption processes. The sorption was found to be predominantly reversible. Cs+ was sorbed much stronger than Sr++in all samples. © 1988, Walter de Gruyter. All rights reserved.
Open Access
Superficial deep-water sediments of the Eastern Marmara Basin
(Springer-Verlag, 1989) Evans, G.; Erten, H.; Alavi, S. N.; Von Gunten, H. R.; Ergin, M.
Superficial sediments (top ∼ Im) of the Eastern Mediterranean Basin, Sea of Marmara, Turkey accumulated rapidly (0.087 ± 0.012 g/cm2 · y) by hemipelagic sedimentation with only limited amounts of gravity flow or bottom current action under low oxygenated but not anoxic conditions. They have restricted faunas, relatively higher organic carbon (1-1.8%) and lower calcium carbonate (14-20%) contents than other Eastern Mediterranean Basin sediments. Sedimentation shows little change over the last millenium except for an increase in Cu, Zn, Pb, Cr, and P over the last few centuries. The increase was most likely caused by increased metallurgical activities since the eighteenth century but are not at sufficient levels for the area to be regarded as polluted. © 1989 Springer-Verlag New York Inc.
Open Access
Sorption of barium on kaolinite, montmorillonite and chlorite
(Royal Society of Chemistry, 1989) Eylem, C.; Erten, H. N.; Göktürk, H.
The sorption characteristics of the Ba2+ ion on kaolinite, montmorillonite and chloritetype clays were studied using the batch method. Barium-133 was used as a tracer. The Ba2+ ion concentrations ranged from 10-8 to 10-5 mol l-1; synthetic groundwater was used and the grain size of all the solid particles was <40 μm. About 6, 8 and 12 d of shaking were necessary to reach equilibrium for chlorite, kaolinite and montmorillonite, respectively. The sorption isotherms were described best by Freundlich and Dubinin - Radushkevich type isotherms. Sorption was predominantly reversible for kaolinite and partly reversible for montmorillonite and chlorite.
Open Access
Coupled-arrangement-channel method for time-dependent wave-packet description of three-body dynamics
(American Physical Society, 1990) Kuruoğlu, Z. C.
An alternative discretization method treating rearrangement and breakup channels on equal footing is introduced for wave-packet description of three-body dynamics. The permutational symmetry for three identical particles is incorporated into the evolution equations of the proposed method. The method is tested on a model three-particle problem that exhibits both rearrangement and breakup channels. Sharp-energy S matrix elements over a broad range of energies above the breakup threshold are extracted from a single wave-packet calculation. © 1990 The American Physical Society.
Open Access
Sorption-desorption behaviour of barium on clays
(Elsevier, 1990) Eylem, C.; Erten, H. N.; Göktürk, H.
Batch experiments were performed to study the sorption behaviour of Ba2+ ion on three different clay minerals determined to be predominantly kaolinite, montmorillonite and mixed chlorite-illite. Synthetic groundwater was used and the concentration of Ba2+ ion was in the range of 10−8 to 10−4 N. Grain sizes of the solid particles were all <38 μm. Cation exchange capacities were obtained using the silver-thiourea (AgTU) method. The variation of RD values was studied as a function of contact time, shaking rate, Ba2+ ion concentration, v/m ratio and pH. The saturation time varied with each type of clay; about 6, 8 and 12 days of shaking time were necessary for chlorite-illite mixed clay, kaolinite and montmorillonite respectively. Shaking rate affected only the rate of sorption and not the saturaton RD values. Sorption was found to be reversible on kaolinite and partly reversible on montmorillonite and chlorite-illite clays. The variation of RD as a function of Ba2+ ion concentration exhibited characteristic inverse S-shaped curves suggesting the presence of at least two different types of exchange sites. Sorption of Ba2+ ion was observed to depend on pH and v/m ratio. The sorption isotherms were found to fit Freundlich and Dubinin-Radushkevich type isotherms well.
Open Access
Wave-packet calculation of sharp-energy S-matrix elements for a three-body system in the breakup regime
(American Physical Society, 1990) Kuruoglu, Z. C.; Levin, F. S.
Sharp-energy S-matrix elements have been successfully extracted from a wave-packet description of three-boson and quartet-spin, neutron-deuteron scattering at energies well above the breakup threshold. Essential to the success of this procedure is use of an expansion basis comprising functions from each of the three two-cluster arrangements. © 1990 The American Physical Society.
Open Access
Sorption Studies of Radioiodine on Soils with Special References to Soil Microbial Biomass
(1991) Bors J.; Erten H.; Martens, R.
In batch experiments with two types of soils, chernozem and podzol, radioiodine (125I) showed an initial rapid sorption, followed by a long and slow further increase. Very little sorption (Rd < 1) was detected in clay minerals. Generally, higher. Revalues were observed for the chernozem soil, characterized by a higher amount of organic substance and of soil biomass. The sorption process was predominantly irreversible, the isotherms were linear at low ion concentrations and deviated from linearity starting at 10-5 mmol - ml-1. Sorption ratio was found to increase with increasing volume to mass ratio. The composition of liquid phases (bidistilled water, synthetic soil water, rain water) highly affected iodine sorption. In experiments with KBr solution, the sorption of I “ was found to be strongly preferred to Br”. Incubation of soil samples under varied conditions (decreased or increased soil biomass, 02-concentration, incubation temperature, soil water content and storage conditions) delivered indications for the participation of soil microflora in iodine immobilization. Test with isolated soil bacteria and fungi showed that radioiodine can be incorporated by soil microorganisms under certain conditions only: Considerable uptake of radioiodine was found in washed (NaCl, CaCl2) cells with both bacteria and fungi, but no incorporation was detected into cells incubated with radioiodine in the culture medium. © 1991, Walter de Gruyter. All rights reserved.
Open Access
Theories of intramolecular vibrational energy transfer
(1991) Uzer, T.; Miller, W. H.
Intramolecular vibrational energy transfer is a process central to many physical and chemical phenomena in molecules. Here, various theories describing the process are summarized with a special emphasis on nonlinear resonances. A large bibliography supplements the text. © 1991.
Open Access
Simulation of the breakup channel in three-particle collisions with pseudoreaction channels
(1991) Kuruolu, Z.C.
A pseudochannel extension of the coupled-reaction-channel (CRC) method is investigated formally and numerically as a means of simulating the effect of the breakup channel on the rearrangement amplitudes. The equations of the pseudostate-augmented CRC method are derived within a two-Hilbert-space approach. The connection of the effective CRC transition operators with the postform transition operators of the formal scattering theory is established. Alternative formulations of the method corresponding to different ways of treating the nonorthogonality interaction are given. Convergence with respect to the number and nature of the pseudostates are investigated numerically on a solvable three-particle model. It is observed that the results obtained with six distinct sets of pseudochannels that have considerably different threshold energies converge toward the exact ones. © 1991 The American Physical Society.
Open Access
Pseudostate description of breakup in the coupled-reaction-channel method: Numerical study of nonorthogonality effects
(1991) Kuruolu, Z.C.
To simulate the effects of the breakup channel on rearrangement amplitudes, the conventional coupled-reaction-channel (CRC) expansion is augmented by pseudoreaction channels. The construction of the projector for the extended CRC space is discussed, and transition-operator equations on this space are given. By solving the full and post-approximation forms of the CRC equations for a model three-particle problem, the crucial role played by the nonorthogonality terms is demonstrated. © 1991 The American Physical Society.
Open Access
Coupled-reaction-channel calculation of a model n-d scattering problem above the breakup threshold
(1991) Kuruolu, Z.C.
An s-wave local potential model of n-d scattering at collision energies above the breakup threshold is solved using a pseudochannel extension of the coupled-reaction-channel method. Results obtained for both quartet and doublet scattering agree within a few percent with the benchmark solutions of Friar et al., Phys. Rev. C 42, 1838 (1990), for the same model. © 1991 The American Physical Society.
Open Access
Isomeric yields of130Sb, 132Sb, 134I, and 136I in the thermal neutron fission of235U
(Kluwer Academic Publishers, 1992) Erten, H. N.
Isomer yield ratios of130Sb,132Sb,134I and136I isomers formed in the thermal neutron fission of235U have been calculated from our previous experimental studies that led to the identification of these species. In those studies the iodine and antimony fractions formed in fission were rapidly separated and the decay of γ-rays belonging to each isomer pair were followed using Ge(Li) detectors and a multichannel analyzer. The isomer ratios were calculated from growth and decay considerations of these γ-rays. The results are compared with the recently published values obtained with an on-line isotope separator, those from LOHENGRIN, and those from model calculations. Angular momenta of fission fragments corresponding to the measured isomer yields have also been calculated.
Open Access
Fine structure of mass and charge distribution in low energy fission
(Akademiai Kiado Rt., 1992) Erten, H. N.; Aras, N. K.
Studies of finer details in mass and charge distribution fission leads to a better understanding of the fission process. Experimental determination of independent and cumulative yields using radiochemical techniques as well as mass spectrometers and fission product recoil separators form the basis of such studies. It has been established that closed shells as well as an even number of nucleons influence both mass and charge distributions. The magnitudes of these effects may be estimated from existing experimental yield data and various fission models. Using our measurements of several fission yields and those existing in the literature we have calculated even-odd proton and neutron effects for various low energy fissioning systems. Where enough data existed, direct calculations were made, whereas for other cases the Zp-model of WAHL has been used. It is found that the even-odd proton effect is well established and pronounced in thermal neutron fission of235U and233U. Lesser effects were found for reactor neutron induced fission of232Th, thermal neutron fission of239Pu and spontaneous fission of245Cm and249Cf. No effect seems to exist in the thermal neutron fission of241Pu and the spontaneous fission of252Cf. The even-odd neutron effect is found to be much lower than the corresponding proton effect in235U and233U fissions and is nonexistent in the rest of the fissioning systems.
Open Access
Wave-packet propagation in momentum space: Calculation of sharp-energy S-matrix elements
(1992) Kuruoǧlu, Z.C.; Levin F.S.
This paper examines momentum-space methods as a means of implementing a scattering-theoretic, long-time lemma on the extraction of sharp-energy S-matrix elements from a wave-packet description of collisions. In order to concentrate on the momentum space and computational aspects, the collision system studied is that of two particles; each has the mass of a nucleon. The formulation of the problem in momentum space avoids any spreading of the packets and allows for a straightforward analysis, which proceeds as follows. First, a time discretization is introduced, so that a conditionally stable, recursive, time-evolution scheme can be employed. The momentum dependence of the full wave packet is next expressed via an expansion in locally defined interpolating polynomials (here, piecewise quadratics), as in the finite-element method. Once the time evolution has progressed sufficiently, the S-matrix element S0(q) can be extracted from the ratio of the qth momentum components of the full and free wave packets. It is essential here that the numerically propagated free wave packet be used in this ratio, since otherwise numerical errors induced in the full wave packet are not canceled, and S0(q) can become as large as 2 or more. Wave packets with central momenta q0 equal to 1, 2, and 4 fm-1 (energies ranging from about 30 to 500 MeV) have been studied, and the behavior of the wave packets and S0(q) for several time intervals, extraction times, numbers of mesh points, etc., have been explored. In general, results with errors of less than at most a few percent are easily obtainable. © 1992 The American Physical Society.
Open Access
Determination of electron affinity of phenyl radical by dissociative electron attachment technique
(John Wiley & Sons, 1993-03) Hacaloglu, J.; Gaines, A.; Süzer, Şefik
Open Access
Analysis of polymers using evolved-gas and direct-pyrolysis techniques
(Royal Society of Chemistry, 1994) Fares, M. M.; Yalcin, T.; Hacaloglu, J.; Gungor, A.; Süzer, Şefik
Thermal analysis of polystyrene, poly(p-methylstyrene) and poly(α-methylstyrene) has been carried out using evolved-gas analysis by infrared and mass spectrometry, and direct-pyrolysis analysis by mass spectrometric techniques. Evolved-gas analysis, both by infrared and mass spectrometry, reveals features due mainly to the corresponding monomers or stable, volatile, and low relative molecular mass degradation products. In direct-pyrolysis mass spectrometry, however, primary decomposition products and heavier fragments such as dimers and trimers can also be detected. The ion-temperature profiles of the corresponding monomer ions reveal information about the thermal stability of the polymers.
Open Access
Radiochronology of sediments from the Mediterranean sea using natural 210Pb and fallout 137Cs
(Kluwer Academic Publishers, 1994) Tadjiki, S.; Erten, H. N.
The210Pb and137Cs profiles of sediment cores from two locations in southern Spain, three locations in southern Turkey and two locations in northern Cyprus were determined by direct γ-ray spectroscopy. Sedimentation rates were derived for all locations using the210Pb data. The rates range from 1.39±0.12 cm · y-1 (0.50±0.04 g · cm-2 · y-1) to 0.08±0.01 cm · y-1 (0.039±0.003 g · cm-2 · y-1). Except for one core, the137Cs profiles were also used to compute sedimentation rates. The results are in good agreement with those of210Pb values. The results of the Constant Initial Concenration and Constant Rate of Supply dating models are in good agreement with each other. The flux of unsupported210Pb varies between 0.11±0.03 to 0.74±0.01 pCi · cm-2. The average depositional flux was found to be considerably lower for cores from the Eastern Mediterranean. © 1994 Akadémiai Kiadó.