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Ethylenebisdithiocarbamate fungicides
Differential thermal analysis
Abstract
DTA curves were run for the ethylenebisdithiocarbamate fungicides maneb, mancozeb and zineb in a nitrogen atmosphere. Zineb produces a curve quite different from the others, with weak endothermic peaks at 166°C, 252°C and 293°C. Maneb and mancozeb have a relatively strong endothermic peak at 185–190°C corresponding to carbon disulphide evolution and a weaker endothemic peak at 290°C corresponding to hydrogen sulphide evolution. Maneb samples and some mancozeb samples also had a minor endothermic peak at 235°C, but this peak was lost after solvent extraction, which proved that it was due to an impurity or impurities. Elemental sulphur was found in the extract and on mixing sulphur with mancozeb, the peak at 235°C made its appearance. There is no distinguishing feature between the DTA curves for maneb and mancozeb. The shapes of the curves are, within experimental limits, indistinguishable, which means that the temperatures and energies of decomposition are the same. The chemist is left with the question whether differences in structure between maneb and mancozeb should lead to different DTA curves.
Abstract
A radiometric study of the kinetics of the displacement reaction between nickel(II) and65Zn-labeled zinc salt of ethylenediaminetetraacetic acid, which was previously used by the authors for the analysis of trace quantities of nickel, has been carried out under varying conditions of temperature, pH etc. The above reaction was confirmed to be first order with respect to both Ni2+ and to*ZnEDTA. The overall reaction rate constant, kf, has been shown to be inversely proportional to the concentration of Zn2+ and directly proportional to the concentration of H+. From the dependence of the rate constant on the concentration of Zn2+ and H+ a three-step mechanism is proposed for the above reaction. The values for Ea, ΔH‡, ΔG‡ and ΔS‡ for the overall reaction have been computed from the experimental data.
Abstract
Heteropolymolybdic acid species of a variety of elements bind to Sephadex (dextran cross-linked by epichlorohydrin). Solution pH can be used as a variable to influence the formation of heteropolymolybdates and thus their affinity for Sephadex. Therefore this material may be used to chromatographically separate certain elements which have been reacted with molybdate in solution. In this paper we report the measurement of distribution coefficients on Sephadex for heteropolymolybdates of As, P, Ge, Si, and Se for solutions of varying pH. We also describe the application of the technique to the recovery of32Si from proton-irradiated KCl targets and68Ge from proton-irradiated molybdenum targets.
Abstract
The Esk estuary, U.K. receives inputs of dissolved and particulate plutoniun from discharges of waste into the Irish Sea from the Sellafield nuclear fuel reprocessing plant. Field and laboratory methods have been developed to examine the phenomenon of rapid plutonium remobilization from contaminated Esk sediments during estuarine mixing which was first identified in 1981.Both types of studies have shown comparable, non-conservative behavior for the two oxidation state categories of238Pu and239,240Pu (i.e. Pu (III/IV) and Pu (V/VI)) with enrichment in low salinity waters due to desorption of plutonium from resuspended sediments.
Abstract
The178m2Hf nucleus, with its long half-life (31 y) and high-spin isomeric state (16+) is desired for new and exotic nuclear physics studies. The Los Alamos Radioisotope Program irradiated a kilogram of natural tantalum at the Los Alamos Meson Physics Facility in early 1981. After fifteen years of decay, this target was ideal for the recovery of178m2Hf. There was more than a millicurie of178m2Hf produced during this irradiation and there has been a sufficient period of time for most of the other hafnium radioisotopes to decayed away. Traditionally, separation techniques for recovering hafnium isotopes from tantalum targets employ solvent extractions with reagents that are considered hazardous. These techniques are no longer condoned because they generate a mixed-waste (radioactive and hazardous components) that can not be treated for disposal. In this paper we describe a new and unique procedure for the recovery of hafnium radioisotopes from a highly radioactive, proton irradiated, tantalum target using reagents that do not contribute a hazardous waste component.
Summary
Germanium-68 (270.8 d, EC 100%) is the parent nuclide of 68Ga, a β+ emitter important to positron emission tomography (PET). 68Ge is obtained by a (p,x) induced nuclear reaction on natural Ga. A typical Ga target assembly consists of liquid Ga contained in a Nb capsule, since Nb is one of the few metals resistant to liquid Ga. Zirconium-88 (83.4 d, via 93Nb(p, α2n)) is one longer-lived radioisotope generated by the proton irradiation of naturally mono-isotopic 93Nb. It decays into 88Y, which, in turn, has been considered a useful radiolabel surrogate for 90Y in the investigation of radiolabeled compounds for cancer radioimmunotherapy. This paper introduces a wet chemical procedure for the processing of Nb/Ga target capsules and the simultaneous recovery of 68Ge and 88Zr.
Abstract
Since the mid-1970s the Los Alamos Medical Radioisotope Program has been irradiating target materials to produce and recover radioisotopes for applications in medicine, environmental science, biology, physics, materials research, and other disciplines where radiotracers find utility. By necessity, the chemical processing of targets and the isolation of radioisotopes generates radioactive waste materials. In recent years there have been federal mandates requiring us to discontinue the use of hazardous materials and to minimize radioactive waste volumes. As a result, substantial waste reduction measures have been introduced at the irradiation facility, in processing approaches, and even in the ways the product isotopes are supplied to users.
Abstract
This study investigates two lanthanide compounds (La3+ and Sm3+) obtained in water/ethyl alcohol solutions employing the anionic surfactant diphenyl-4-amine sulfonate (DAS) as ligand. Both sulfonates were characterized through IR, TG/DTG (O2 and N2). The thermal treatment of both compounds at 1273 K under air leaves residues containing variable percentages of lanthanide oxysulfide/oxysulfate phases shown by synchrotron high-resolution XRD pattern including the Rietveld analysis. The phase distributions found in the residues evidence the differences in the relative stability of the precursors.
Summary
As a follow up to the initial 1998 intercomparison study, a second study was initiated in 2001 as part of the ongoing evaluation of the capabilities of various ultra-sensitive methods to analyze 239Pu in urine samples. The initial study1 was sponsored by the Department of Energy, Office of International Health Programs to evaluate and validate new technologies that may supersede the existing fission tract analysis (FTA) method for the analysis of 239Pu in urine at the µBq/l level. The ultra-sensitive techniques evaluated in the second study included accelerator mass spectrometry (AMS) by LLNL, thermal ionization mass spectrometry (TIMS) by LANL and FTA by the University of Utah. Only the results for the mass spectrometric methods will be presented. For the second study, the testing levels were approximately 4, 9, 29 and 56 µBq of 239Pu per liter of synthetic urine. Each test sample also contained 240Pu at a 240Pu/239Pu atom ratio of ~0.15 and natural uranium at a concentration of 50 µBq/ml. From the results of the two studies, it can be inferred that the best performance at the µBq level is more laboratory specific than method specific. The second study demonstrated that LANL-TIMS and LLNL-AMS had essentially the same quantification level for both isotopes. Study results for bias and precision and acceptable performance compared to ANSI N13.30 and ANSI N42.22 have been compiled.
