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  • Author or Editor: P. Aggarwal x
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Abstract  

234U/238U α-activity ratios determined by α-spectrometry (AS) and those calculated from the atom ratio data using the half-life values are compared in some of the isotopic reference materials of uranium and a few other uranium samples. For α-spectrometry, electrodeposited sources were prepared and a large area passivated ion implanted (IPE) detector (450 mm2) was used for recording the α-spectra. The isotopic composition of U was determined by thermal ionisation mass spectrometry (TIMS) and the recommended half-life values of234U and238U were used to calculate the α-activity ratio. It is observed that234U/238U α-activity ratios calculated from the atom ratio data are consistently high, with a mean difference of about 5%, when compared to the α-spectrometry results. This discrepancy warrants confirmation by a few more laboratories and suggests redetermination of the half-life values of234U and238U.

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Abstract  

Corn cobs obtained as waste from the corn industry, were analyzed by a TG-DTA unit in an atmosphere of flowing nitrogen. The carbonaceous products so formed were then produced on a preparative scale and activated chemically using potassium hydroxide. This resulted in the formation of a carbon with a very high surface area. The active carbon produced was then examined using thermal analysis in the temperature jump mode on a thermogravimetry unit. From this data the kinetics of degradation of the active carbon was determined using zero order rate kinetics. The pore structure of the active material was also examined using SEM. TheE a for activated corn cobs was found to be 106 kJ mol−1.

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Abstract  

Simultaneous TG-DTA units have a work station which allows plots to be made of temperature against time, as well as the conventional TG and DTA plots. These time-temperature plots and their derivatives can be used to show details of both exothermic and endothermic events. The melting behavior of zinc is used as illustrative of endothermic phase changes. Solid-solid transitions are exemplified by noting the transitions in quartz. Examples of chemical reactions being treated to temperature-time plots are the decomposition's of zinc oxalate in nitrogen (an endothermic event) and the oxidation of carbon black in air (a sustained exothermic event). This wide selection of exothermic and endothermic events serves to illustrate the details which can be drawn from any thermogravimetric plot irrespective of the other associated equipment present, which serves to reinforce the data presented in the present study.

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Abstract  

234U of high isotopic purity (>99 atom%) as well as of high radiochemical, purity was separated from aged238Pu prepared by neutron irradiation of237Np. Methodologies based on ion exchange and solvent extraction procedures were used to achieve high decontamination factor from238Pu owing to the very high α-specific activity of238Pu (2800 times) in comparison to that of234U. Isotopic composition of purified234U was determined by thermal ionisation mass spectrometry. Alpha spectrometry was used for checking the radiochemical purity of234U with respect to concomitant α-emitting nuclides. The separated234U will be useful for different investigations using mass spectrometry and alpha spectrometry.

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Abstract  

Ingredients used in the manufacture of perfumes can be investigated by thermogravimetry. In this study the evaporation of methyl benzoate was investigated using a simultaneous TG-DTA unit. A rising temperature method of thermal analysis was used for the study. The rate of evaporation of the ingredient was calculated from a simple plot of percentage mass lossvs. time. A derivative plot of the same was used to calculate the coefficient of evaporation in a controlled atmosphere and regulated air flow rate. In a series of programmed temperature runs on the TGDTA unit it was shown that the evaporation process is zero order, and that the evaporation coefficients at each temperature can be fitted into the Arrhenius equation. The energy of activation, Eact can be calculated from the slope of the line. It was found to be 47 kJ mol−1. This value was compared and shown to approach the enthalpy of vaporization as calculated using the Troutons or Clausius Clapeyron equation

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Abstract  

The degradation of cellulose and starch samples in air and nitrogen has been investigated by thermal analysis techniques. The techniques employed were differential thermal analysis, rising temperature and temperature jump thermogravimetry. Rate data were obtained from these experiments and Arrhenius parameters calculated from these values. This data was used to determine the mechanism by which the cellulose and starch samples degraded. The Arrhenius parameters were also calculated. The behavior of starch and cellulose upon thermal analysis were compared and are reported.E act for corn starch was found to be 474 kJ mol−1 and for a cellulose 242 kJ mol−1.

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Abstract  

Determination of americium is one of the requirements of chemical quality assurance of plutonium bearing fuel materials. Alpha-spectrometry is generally used for the determination of 241Am in Pu bearing fuels since the efficiency of semiconductor detector used for alpha-spectrometry is independent of the alpha-particle energy in the 4 to 8 MeV range. However, this method has limitations for Pu samples containing extremely small or very large amounts of 241Am. Thus an alternative methodology based on alpha/gamma (α/γ) activity ratio was developed and tested using different samples. The method is based on the determination of total γ-activity (of 60 keV peak) of an aliquot of the solution and the total α-activity present in the aliquot. The method is fast as it does not involve chemical separation of Pu and Am as required in the alpha-spectrometric method. Data obtained on synthetic and real life samples demonstrates the usefulness of the developed alpha/gamma ratio method for the determination of 241Am in Pu bearing fuel samples.

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Abstract  

Determination of 238Pu in plutonium bearing fuels is required as a part of the chemical quality assurance of nuclear fuels. In addition, the determination of 238Pu is required in nuclear technology for many other applications, e.g., for developing isotope correlations and while using 238Pu as a spike (tracer) in isotope dilution α-spectrometry (IDAS). This determination usually involves the use of α-spectrometry on purified Pu sample. In view of the random errors associated with the counting statistics and the systematic errors due to (1) in-growth of 241Am in purified Pu sample and (2) tail contribution correction methodology in α-spectrometry, the precision and accuracy obtainable by α-spectrometry are limited. Thermal ionization mass spectrometry (TIMS) is generally used for the determination of different Pu isotopes other than 238Pu. This is due to the ubiquitous isobaric interference from 238U at 238Pu in TIMS. Recently, we have carried out studies on the formation of atomic and oxide ions of U and Pu by TIMS and developed a novel approach using interfering element correction methodology to account for the isobaric interference of 238U at 238Pu in TIMS. This methodology is based on the addition of 235U (enrichment >90 atom%) to Pu sample followed by the determination of 238U/235U atom ratio using UO+ ion and determination of Pu isotope ratios using Pu+ ion, from the same filament loading. The TIMS methodology was used for the determination of 238Pu in different Pu samples in U based nuclear fuels from PHWRs with 238Pu content about 0.2 atom%. The 238Pu determination was also carried out using α-spectrometry. This paper reports the results obtained by the two methods and presents the ments and shortcomings of the two approaches.

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Bipolaris sorokiniana, causal agent of spot blotch of wheat is a hemibiotrophic pathogen. This fungus produced a toxin in culture that induced necrosis not only in wheat but also in barley, sorghum and some weeds. The toxic compound purified by prep TLC from culture filtrate of virulent strain BS-75, characterized using NMR and GC-MS techniques, was identified to be ‘Bipolaroxin’, which is a first report of its production by B. sorokiniana infecting wheat. It is a bicyclical sesquiterpene belonging to family Eremophilane. Besides producing necrotic lesions on wheat, toxin (30 ng/ml) caused necrotic lesions on barley, maize, sorghum, Phalaris minor, Avena sativa and Cynodon dactylon as studied using leaf infiltration bioassay. Qualitative and quantitative differences among the pathogenically variable isolates were observed with respect to toxin production by TLC and HPLC. Different isolates produced bipolaroxin in the range of 0.05 µg/ml (BS-41) to 1.4 µg/ml (BS-75).

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Abstract  

Experimental evaluation of a commonly used silicon surface barrier detector and of the recently introduced passivated ion implanted detector for alpha spectrometry is reported in terms of FWHM, peak to valley ratio, tail parameter and % tail contribution per unit alpha activity ratio using electrodeposited sources of plutonium prepared on platinum backing material. For this purpose, detectors of nearly the same diameter were employed (100 mm2 silicon surface barrier detector with a diamater of 1.13 cm and 80 mm2 passivated ion implanted silicon detector with a diameter of 1.01 cm). It is shown that the recently introduced passivated ion implanted detectors give smaller tailing effects. But there is no significant difference between the two detectors used in the present work w.r.t. FWHM and peak to valley ratios. Further, it is observed that the peak to valley ratio can be used to get an idea about240Pu/239Pu and241Am/238Pu alpha-activity ratios in the sample.

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