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Abstract  

Tracer experiments on the transfer of carbon from culture solution to Daphnia magna through phytoplankton have been carried out using 13C and infrared absorption method. The purpose of this experiment is to investigate the experimental systems for the use of 13C in aquatic system. Daphnia magna was cultured in a 100 ml of solution containing phytoplankton and 20 mg of NaH13CO3 for 24 hours in the light and dark conditions (2000 lux, 14 hour light and 10 hours dark at 25 C). The concentration of 13C in Daphnia magna under light condition was about 2.0% (atom% excess), while in the dark condition 13C tracer was not detected. The concentration of 13C in phytoplankton under light condition was around 20%. It was suggested that 13C added as carbonate in the culture solution was photosynthetically assimilated by phytoplankton and then transferred to Daphnia magna. Using this system, the effect of UV-B exposure on the 13C uptake of Daphnia magna has been examined. The UV-B intensity was 95 mW/cm2 and exposure time was 15, 30, and 60 minutes. The concentration of 13C in Daphnia magna decreased with increasing exposure time. The Daphnia magna exposed to UV-B for 15 minutes intakes phytoplankton as much as control, while 30 minutes and 60 minutes exposures were lower than control. The lower concentrations of 13C observed in Daphnia magna were due to less intake of phytoplankton caused by the UV-B exposure.

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A method has been developed for routine determination of cadmium in zinc ores by thermal neutron absorption analysis, based on the attenuation of a thermal neutron flux passing through a neutron absorbing material. The thermal neutron flux is related to the52V-activity induced in a vanadium detector, surrounded by pellets pressed from a mixture of powdered material with graphite. Besides cadmium, also the major constitutents zinc, iron and sulfur contribute significantly to the total attenuation of the thermal neutron flux. Calibration lines for these elements are worked out. All irradiations are carried out for 200 s in the partially thermalized neutron flux of a 5 Ci227Ac—Be isotope neutron source. After a decay of 30 s, the52V-activity of the vanadium detector is measured for 400 s with a NaI(T1) scintillation detector. The analysis sequence, including the computation of the results from the counting data, is automated by means of a LSI—11 microprocessor with 12K×16 bit memory. Zinc ores, containing 0.02 to 1.45% cadmium, have been analyzed with a precision ranging from 12.6% to 0.54% relative. As a test for the reliability of the method, two NBS standard reference materials were analyzed in the same way as the zinc ore samples.

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Abstract  

A series of different commercial membranes were characterized by their moisture absorption and desorption properties under controlled humidity and temperature conditions. This work was made possible by combining the features of a constant humidity conditioning chamber with those of a thermogravimetric (TG) apparatus. These two modules were interconnected by tubing, rotameters, an atmosphere-recycling microbellows pump and switching valves. Under programmed heating and isothermal conditions reproducible data were obtained in terms of weight-gain or weight-lossvs. time and pore size. Evaluation of the resulting TG curves allowed us to report reasonable differences in the materials, some of which had been previously surface-modified by the manufacturer.

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Summary  

99mTc compounds play a very important role in modern medicine. These compounds are among the most widely used radiopharmaceuticals. Unfortunately, due to the necessity of working with small quantities of materials, the chemistry of these materials is not completely understood. Currently, the structure of the 99mTc-DTPA (a common renal imaging agent) is unknown. In this paper, we show that X-ray absorption spectroscopy (XAS) can be used to determine the structure of Tc ycompounds b comparing XAS results to those from X-ray diffraction (XRD). Specifically, XAS data and fits for TcCl6 2-, TcOCl4-, and TcNCl4- were found to be in excellent agreement with the known structures from XRD. Finally, we show the XAS spectrum from a 77 ng sample of 99Tc-DTPA. To our knowledge this is the first XAS spectrum taken from this material. The near-edge region (XANES) was visible after a single scan on this material. This clearly indicates that we will be able to determine the local atomic structure of this material.

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The absorption kinetics for uranium into blood after deposition as tri-n-butylphosphate (UTBP) in the rat lung were combined with human data on particle deposition and clearance from the ICRP Publication 66 respiratory tract model and information from the most recent ICRP biokinetic model for uranium to predict the consequences for exposure of workers. These predictions suggest that, (1) the biokinetics of UTBP are similar to those for a Type F compound as defined by ICRP, (2) the dose coefficient is essentially independent of the aerosol size and isotopic composition, (3) the mass of uranium equivalent to the ALI can vary by 13 fold depending upon the isotopic composition, (4) intakes of uranium as UTBP other than chronic intakes as highly enriched forms should be restricted on the basis of the chemical toxicity of uranium, (5) the assessment of intake by urine bioassay measurements should be interpreted with caution unless the exposure conditions are well defined and (6) severe kidney damage is unlikely at intakes corresponding to the ALI or daily limit.

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Practical application of oow energy gamma rays and X-rays in I.N.A.A. was restricted because of the complexity of the X-ray spectrum and sample self-absorption. This paper describes a method for the calculation of sample self-absorption on the basis of the actual sample spectra only, as measured with a high resolution semiconductor X-ray detector. In the 20–400 keV energy range, the attenuation coefficient can be represented by a three parameter function of photon energy. This was verified by measuring the transmission of photons of different energies through a range of materials. Experiments with neutron irradiated U.S.G.S. standard reference materials with known major oxide composition showed that self-absorption thus calculated from the observed spectra is in good agreement with the results of theoretical calculations based on known attenuation coefficients.

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The transmission of 0.766 MeV beta-particles emitted from 204Tl through aluminum has been investigated for different arrangements of point source, absorber and detector. In the first arrangement, the mass absorption coefficient (μ m) has been measured as a function of the absorber to the source distance (H AS), when the absorber foil was placed just above the window of a surface barrier solid state detector. In the second arrangement, the mass absorption coefficient has been measured as a function of the absorber to detector distance (H AD), when the absorber foil was placed just on the source. The measured mass absorption coefficients of beta-particles have been compared to the values gained in a previous work.

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In order to investigate the self-absorption of the -rays from 14C in a gel-suspension sample, the Monte Carlo code, simulating the sequence of stages occurring in the sample, has been developed. The trajectory of the electron was calculated by the continuous slowing down approximation and the multiple Coulomb scattering theory. The effects of the self-absorption, strong quenching and particle size distribution of calcium carbonate on the output counting efficiency and the shape of the energy spectrum were evaluated.

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Abstract  

Instrumental neutron activation, atomic absorption spectroscopy and conventional methods of analysis were used on eight different silicate rocks and two minerals. Trace elements and major constituents were determined. It was considered that the methods should be regarded as complementary analytical techniques.

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The diffusive and dynamic mechanical behavior of the DGEBA/1,3-BAC epoxy resin system was studied during water absorption. The diffusion of water was investigated at 100% relative humidity, by immersion of specimens in water at 60, 80 and 100°C. In all absorption experiments, water diffusion followed Fick's law. Diffusion coefficients and saturated water concentrations are given for these temperatures. The activation energy for diffusion was determined from the relationship between the diffusion coefficient and the reciprocal of the absolute temperature. The value obtained was 31.2 kJ mol−1. Dynamic mechanical analysis of samples immersed in 100°C water and with various water contents showed both a shift of Tg, defined by thetanδ peak, to lower temperatures and a slight decrease in the dynamic modulus in the presence of water. These effects are probably a result of plasticization.

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