A method for the simultaneous estimation of228Th and229Th

A simple method is reported in this paper to estimate²²⁹Th in the presence of²²⁸Th. The total activity of²²⁹Th and²²⁸Th was determined by following the alpha activity growth (using a liquid scintillation counter and proportional counter) of purified thorium samples. The activity ratio of²²⁹Th/²²⁸Th was determined by alpha spectrometry. From the initial total activity and ratio, disintegration rates of²²⁹Th and²²⁸Th were calculated. The values obtained for the activities have a precision better than ±2%.     

Mass yields in 229Th(n,f)

Cumulative yields of 27 fission products have been determined in ²²⁹Th(n,f) by recoil catcher technique followed by gamma-ray spectrometry. Absolute fission yields were arrived at from the fission rate measured by track etch counting method. Mass yields were obtained from the cumulative yields using the charge distribution parameters reported in the literature. The values agree well with the reported values obtained both by physical and radiochemical methods. The resulting asymmetric mass distribution shows strong fluctuation in the yields in the light and heavy wings with a periodicity of five mass units.     

Dissolution of ThO2: study of dissolution process with initial 229Th spike

Journal of Radioanalytical and Nuclear Chemistry - The sparingly soluble ThO2 dissolution behaviour was studied under conditions that are expected to prevail in bedrock after the closure of the...     

Spanning set of silica cluster isomer topologies from QTAIM

Structural and chemical properties of the building block of silica nanowires, (SiO(2))(6), are investigated with the theory of atoms and molecules (QTAIM). Twenty-five conformers have been analyzed, ten of which have not been reported before. We extend the silica (SiO(2))(6) topology phase space using QTAIM; the Poincaré-Hopf topological sum rules are applied and used to identify the spanning set of topologies, and this includes finding eight new distinct topologies that satisfy the Poincaré-Hopf relation. A simple phase diagram of the solutions of the Poincaré-Hopf relation is created with the aid of a new classification scheme to determine the boundary between topological stability and instability. Sum rules are then found to be applicable to any set of isomers. We determine that O-O bonding interactions exist for the silica (SiO(2))(6) conformers in regions where the energy surface is flattest. In addition, we identify unstable local minima in the topology of the charge density in order to further compare conformer instabilities. We quantify the dimensionality of a molecule using the Poincaré-Hopf relation instead of Euclidean geometry. This quantum topological definition of geometry shows that the four most energetically stable (SiO(2))(6) conformers are quantified as two-dimensional within the new quantum topology.     

Dihydroagarofurans: the fourth isomer isolated from Cedrelopsis grevei bark oil

4-Epi-cis-dihydroagarofuran was isolated from the bark oil of Cedrelopsis grevei and its structure was elucidated by 1D and 2D-NMR spectroscopy.     

Synthesis of an isomer of the renieramycin skeleton from L‐tyrosine

A new approach that tried to obviate the use of bromine protection groups was studied to synthesize (?)‐renieramycin G from L ‐tyrosine. It was found that the first intermolecular Pictet–Spengler reaction proceeded successfully to give the correct tetrahydroisoquinoline precursor 6 . However, the second intramolecular Pictet–Spengler cyclization step failed to give the desired product, and an isomer of the skeleton of the renieramycins was obtained via 12 steps starting from L ‐tyrosine. J. Heterocyclic Chem., (2011).     

Structure of an unsymmetrical isomer from the attempted synthesis of 1,8-dicyclooctatetraenylnaphthalene.

Attempted synthesis of 1,8-dicyclooctatetraenylnaphthalene (1) by the palladium(0)-catalyzed coupling of 1,8-dibromonaphthalene with cyclooctatetraenyltrimethylstannane afforded a single unsymmetrical isomer of 1 in 88% yield. Two-dimensional NMR methods and spectral synthesis were employed to assign the structure of the isomer (2). AM1 geometry-optimized structures of 2 and its isomers showed that the unexpected unsymmetrical structure of 2 results from the minimization of repulsive inter-ring H-H interactions. Compound 2 is postulated to arise via tandem [2 + 2] cycloaddition and 6 pi --> 4 pi + 2 sigma electrocyclization reactions of 1.     

Photodimers of a soluble tetracene derivative. excimer fluorescence from the head-to-head isomer

[reaction: see text] Irradiation of 5,12-didecyloxytetracene (1) leads to photodimers P(1) (planosymmetric) and P(2) (centrosymmetric). P(1) is characterized by naphthalene excimer fluorescence, whereas P(2) emits naphthalene monomer fluorescence.     

An isomer of coronopilin

Conclusions From the racemes ofC. xanthifolia Fresen. have been isolated a sesquiterpene lactone C₁₆H₂₀O₄, the structural (+)-isomer of (–)-coronopilin, which has not been studied previously; structure I has been proposed for it.Khimiya Prirodnykh Soedinenii, Vol. 5, No. 5, pp. 375–377, 1969     

Synthesis of an isomer of the germacranolide isoaristolactone

Photocycloadditlon of (+)-isoplperltenone and cyclobutene-1-carboxylic acid gives an adduct which upon reduction with NaCNBH₃ followed by thermolysis yields an isomer of isoaristolactone in an overall yield of 26%.     

如何求解同分异构体计数问题

用浅显的方法具体实例化地介绍了求解同分异构体计数问题的图论及群论的数学抽象表示和数学原理,以及从生成函数及树型结构计数的概念到结构异构和立体异构两类同分异构体计数问题的求解。最后通过数学软件Maple16的简单编程,给出了具体实现的方法。     

Determination of228Th,230Th,and232Th in environmental samples from uranium mining and milling operations

A method is described for the determination of²²⁸Th,²³⁰Th, and²³²Th in environmental samples from uranium mining and milling operations. The analytical procedure is based on the direct determination of²²⁸Th in the sample by high resolution γ-spectrometry followed by extraction and purification of the thorium fraction using high molecular weight amines and an anion-exchange technique, respectively, prior to α-spectrometry to determine isotopic ratios. The lowest level of detection for each thorium isotope is 0.01 pCi/g for solid samples and 20 pCi/l for aqueous samples. Replicate analyses of a typical mine waste stream gave a standard deviation of ±3% for²²⁸Th. Standard deviations of the²³⁰Th and²³²Th increased to ±11% apparently due to traces of²¹⁰Po interfering in the α-spectrometry.     

Laboratory detection of the elusive HSCO+ isomer

The rotational spectrum of protonated carbonyl sulfide, HSCO(+), has now been detected in the centimeter-wave band in a molecular beam by Fourier transform microwave spectroscopy. Rotational and centrifugal distortion constants have been determined from transitions in the K(a)=0 ladder of the normal isotopic species, and DSCO(+) and H(34)SCO(+). HSCO(+) is systematically more abundant by a factor of three than HOCS(+), the isomer obtained by attaching the H(+) to the other end of the molecule, which ab initio calculations long predicted to be higher in energy by 4-5 kcalmol. Because HSCO(+) is comparable in polarity to HOCS(+) and is apparently more stable and because OCS is widely distributed in astronomical sources, HSCO(+) is a good candidate for detection with radio telescopes.     

Selective catalytic hydrogenation of the trans,trans isomer from a mixture of 2,4-hexadienes.

trans, trans-2,4-hexadiene is quantitatively converted into cis-3-hexene by photoinduced hydrogenation catalyzed by chromium carbonyl complexes in presence of acetone which allows both acceleration and selectivity.