Determination of 129I/127I ratios in environmental samplesusing neutron activation analysis

Studies on the behavior of ¹²⁹I in the environment are greatly enhanced when the concentration of the radioiodine can be related to stable ¹²⁷I. The background ratios of ¹²⁹I/¹²⁷I of 10^-10 and lower, found in uncontaminated areas, are best measured using accelerator mass spectrometry. However, there are many examples of studies where ratios higher than 10^-8 have been measured, even in places located remotely from nuclear reprocessing activities. In the vicinity of reprocessing plants it is possible to find ratios between 10⁰ and 10^-7, which can be detected easily using neutron activation analysis (NAA). Stable iodine is readily determined at concentrations below 1 mg/kg in environmental materials with instrumental NAA and radiochemical techniques can be used to measure ¹²⁹I to below mBq concentrations. Therefore, where there are elevated concentrations of ¹²⁹I it is possible to use a combination of neutron activation techniques to determine ¹²⁹I/¹²⁷I ratios. This paper describes how NAA is used to measure ¹²⁹I/¹²⁷I ratios in milk, vegetation, and atmospheric samples. Instrumental NAA is used to measure both ¹²⁹I and ¹²⁷I where the ratio is between 10⁰ and 10^-3. A radiochemical procedure is used to measure ¹²⁹I at ratios between 10^-3 and 10^-7, with a thermal neutron flux of 10¹⁶ m^-2·s^-1.     

Extractive spectrophotometric determination of nitrite in polluted waters

Nitrite is diazotised with p-nitroaniline in hydrochloric acid and coupled with 8-quinolinol in alkaline medium to give a purple azo dye (λ_max = 550 nm, ? = 3.88 × 10⁴ l mol^-1 cm^-1). Extraction of the dye into 3-methyl-1-butanol shifts the absorption maximum to 570 nm and improves the apparent molar absorptivity to 5.852 × 10⁴ l mol^-1 cm^-1. Beer's law is obeyed for 0.01–0.06 ppm nitrite. The Sandell sensitivity is 0.00078 μg cm^-2. The method is applicable to polluted waters.     

Extraction—spectrophotometric determination of boron with naphthalene-2,3-diol and crystal violet

Boron reacts with naphthalene-2,3-diol to form a complex anion extractable into benzene with crystal violet and is determined indirectly by measuring the absorbance of the crystal violet in the extract at 610 nm. The calibration graph is linear for boron over the range 8.0 × 10^-7–8.0 × 10^-8 mol l^-1; the apparent molar absorptivity is 8.8 × 10⁴ l mol^-1 cm^-1. The method is applied to the determination of boron in natural waters.     

Concentration, distribution and characteristics of depleted uranium (DU) in the Kosovo ecosystem: A comparison with the uranium behavior in the environment uncontaminated by DU

The smear samples of the penetrator were analyzed for the determination of the uranium composition. The obtained relative composition (m/m) of uranium isotopes in all the smear samples is in the range of 99.76-99.78% for ²³⁸U, 0.000659-0.000696% for ²³⁴U, 0.213-0.234% for ²³⁵U, and 0.00274-0.00328% for ²³⁶U, showing characteristics of depleted uranium (DU). The uranium concentrations in Kosovo soil and water samples as well as biological samples were investigated. It was found that the uranium concentrations in the Kosovo soil samples are in the range of 11.3-2.26·10⁵ Bq·kg^-1 for ²³⁸U, 10.3-3.01·10⁴ Bq·kg^-1 for ²³⁴U, 0.60-3251 Bq·kg^-1 for ²³⁵U, and ￡0.019-1309 Bq·kg^-1 for ²³⁶U. The obtained activity ratios are in the range of 0.112-1.086 for ²³⁴U/²³⁸U, 0.0123-0.1144 for ²³⁵U/²³⁸U, and 0-0.0078 for ²³⁶U/²³⁸U, indicating the presence of DU in about 77% of the surface soil samples. At a specific site, the DU inventory in the surface soil is about 140 mg·cm^-2, which is 1.68·10⁶ times higher as the estimated mean DU dispersion rate in the region. The uranium concentrations in Kosovo lichen, mushroom, bark, etc., are in the range of 1.97-4.06·10⁴ Bq·kg^-1 for ²³⁸U, 0.48-5158 Bq·kg^-1 for ²³⁴U, 0.032-617 Bq·kg^-1 for ²³⁵U, and ￡0.019-235 Bq·kg^-1 for ²³⁶U with mean activity ratios of 0.325±0.0223 for ²³⁴U/²³⁸U, of 0.0238±0.0122 for ²³⁵U/²³⁸U, and 0.0034±0.0028 for +U/²³⁸U, indicating the presence of DU in the entire sample. On the contrary, the uranium concentrations in Kosovo water samples are low, compared with the water samples collected in central Italy, indicating the presence of negligible amount of DU. The uranium isotopes in Kosovo waters do not constitute a risk of health at the present time. This revised version was published online in July 2006 with corrections to the Cover Date.     

The determination of trace levels of aluminium by differential pulse polarography

The direct determination of aluminium in aqueous solutions by differential pulse polarography is described. If the pH is carefully controlled to 4.00 ± 0.01, there is a linear relationship between the peak height of the polarographic wave and the aluminium concentration up to 2.5 × 10^-5 mol dm^-3. The coefficient of variation is about 4% at the 10^-5 mol dm^-3 level. With increasing aluminium concentrations, the relationship ceases to be linear, and above 9 × 10^-5 mol dm^-3, the peak splits, probably because of hydrolysis and polymerisation. Na⁺, NH₄⁺, Mg²⁺ and Ca²⁺ interfere at levels 100 times greater than that of the aluminium whereas Fe²⁺, Fe³⁺, Cu²⁺, Zn²⁺, Ni²⁺, NO₃^-, ClO₄^-, Cl^- and SO₄^2- do not interfere.     

Extraction—spectrophotometric determination of palladium(ii) with 2-nitroso-5-diethylaminophenol

An extraction—spectrophotometric determination of palladium(II) with 2-nitroso-5-diethylaminophenol is described. Complex formation and extraction of the complex with chloroform are possible with aqueous phases of about 2.5 M sulfuric acid. The molar absorptivity of the complex is 4.38 X 10⁴ l mol^-1 cm^-1 at 486 nm. Few of the common ions interfere at concentrations of 10^-4–10^-3 M; more than 10^-5 M Ir(IV), 10^-5 M W(VI), 5 × 10^-6 M Au(III) and 10^-6 M iodide cause negative errors. The method can be applied to the determination of palladium in catalysts for automobile exhaust purifiers.     

Determination of uranium isotopes in environmental samples by alpha-spectrometry

A new and accurate method for the determination of uranium isotopes (²³⁸U, ²³⁴U and ²³⁵U) in environmental samples by alpha-spectrometry has been developed. Uranium is preconcentrated from filtered water samples by coprecipitation with iron(III) hydroxide at pH 9-10 using an ammonia solution and the precipitate is dissolved in HNO₃ and mineralized with H₂O₂ and HF; uranium in biological samples is ashed at 600 °C, leached with Na₂CO₃ solution and mineralised with HNO₃, HF and H₂O₂; uranium in soil samples is fused with Na₂CO₃ and Na₂O₂ at 600 °C and leached with HCl, HNO₃ and HF. The mineralized or leaching solution in 2M HNO₃ is passed through a Microthene-TOPO (tri-octyl-phosphine oxide) column; after washing, uranium is directly eluted into a cell with ammonium oxalate solution, electrodeposited on a stainless steel disk and measured by alpha-spectrometry. The lower limits of detection of the method is 0.37 Bq^.kg^-1 (soil) and 0.22 mBq^.l^-1 (water) for ²³⁸U and ²³⁴U and 0.038 Bq^.kg^-1 (soil) and 0.022 mBq^.l^-1 (water) for ²³⁵U if 0.5 g of soil and 1 litre of water are analyzed. Five reference materials supplied by the IAEA have been analyzed and reliable results are obtained. Sample analyses show that, the ²³⁸U, ²³⁴U and ²³⁵U concentrations are in the ranges of 0.30-103, 0.49-135 and 0.02-4.82 mBq^.l^-1 in waters, of 1.01-7.14, 0.85-7.69 and 0.04-0.32 Bq^.kg^-1 in mosses and lichens, and of 25.6-53.1, 26.4-53.8 and 1.18-2.48 Bq^.kg^-1 in sediments. The average uranium yields for waters, mosses, lichens and sediments are 74.5±9.0%, 80.5±8.3%, 77.8±4.9% and 89.4±9.7%, respectively.     

Molekülabsorptionsspektrometrie bei elektrothermischer verdampfung in einer graphitrohrküvette: II. Bestimmung von fluoridspuren in mikrovolumina durch die molekülabsorption von GaF-molekülen

Molecular absorption spectrometry by electrothermal volatilization in a graphite furnace. Part 2. The determination of traces of fluoride by GaF molecular absorption A direct determination of traces of fluoride by measurement of the GaF molecular absorption in a graphite furnace is described. The optimal conditions, for compensation of the non-specific absorption and for temperatures of ashing and volatilization, are discussed. The effects of the Ga³⁺ and Na⁺ concentrations and of several acids on the determination are reported. Increasing concentrations of Ga³⁺ ions increase the concentration of GaF molecules in the graphite furnace plasma. Higher Na⁺-concentrations decrease the loss of HF in the drying time. The detection limit (3 s) is 1.6 ng F^-/10 μl; the sensitivity is 0.8 ng F^-/10 μl for 0.01 absorbance units. The influence of Cl^--, Br^--, J^--, SO₄^2--, BO₃^3--, SiO₃^2--, Li⁺-, K⁺-, Be²⁺-, Mg²⁺-, Ca²⁺-, Al³⁺-, In³⁺-, Zn²⁺-, Cd²⁺- and Fe³⁺- ions on the determination are described.     

Uranium and phosphate behavior in the vadose zone of a fertilized corn field

Phosphate fertilizers contain approximately 200 mg^.kg^-1 of uranium. The uranium and phosphate can move through the vadose zone and reach groundwater. Therefore, the knowledge of the ways in which these two elements are distributed, their partition relationships and their mobility behavior is of great interest. In order to study the latter, suction cup samplers, intended to collect soil water at different depths, were installed in an experimental site in a high plain of Mexico, where corn is cultivated and phosphate fertilizers are systematically applied. It was observed that the vadose zone contains high concentrations of uranium (1-50 mg^.kg^-1) and phosphates (22-33 mg^.kg^-1), which decrease at greater depths. Uranium concentration in the soil water varies between 10 and 3 mg^.l^-1 and phosphates between 1 and 0.3 mg^.l^-1. Their evolution throughout the profile of the vadose zone is determined by the decrease in concentrations, due to the physico-chemical processes involved.     

Spectrophotometric determination of carbon disulphide as the 1,2,3,4-thiatriazol-5-thiolate ion

A simple, precise and selective procedure for the spectrophotometric determination of carbon disulphide in water is described. The method is based on the quantitative formation of the 1,2,3,4-thiatriazol-5-thiolate ion from carbon disulphide and azide. The specific rate for this reaction at ionic strength 4.0 (NaN₃) and 25°C is 8.4·10^-3 mol^-1 s^-1; the kinetic parameters D3H and D3S are 16.7 kcal mol^-1 and —14 cal mol^-1deg^-1, respectively. At the analytical wavelength of 313 nm, the molar absorptivity is 7.27 ·10³ l mol^-1cm^-1. The system obeys Beer's law for 2.3–28.6 g ml^-1 of carbon disulphide. The effects of foreign ions are discussed.     

The simultaneous determination of As,Cd, Co,Hg, Mo,and Zn in fresh water by neutron activation analysis

A radiochemical neutron activation method for the simultaneous determination of arsenic, cadmium, cobalt, mercury, molybdenum, and zinc in fresh water is described. The method is based on anion-exchange separation in hydrochloric acid media followed by simple precipitations. The determination limits, based on analysis of a 5-ml sample without preconcentration, and with a well-type NaI(Tl) detector, are as follows: As, 10^-3 μg l^-1 ; Cd, 6 × 10^-2 μg l^-1 ; Co, 4 × 10^-3 μg l^-1 ; Hg, 7 × 10^-3 μg l^-1 ; Mo, 10^-1 μg l^-1 ; Zn, 2 × 10^-1 μg l^-1. The method is adequate for the analysis of natural fresh waters.     

COMPLEX FORMATION BETWEEN PYRENE AND THE NUCLEOTIDES GMP, CMP, TMP AND AMP

Pyrene has been found to form ground and excited electronic state complexes of 1:1 stoichi-ometry with GMP, CMP, TMP and AMP. The values of their ground state association constants are 45 M^-1, 13M^-1, 14 M^-1, and 52 M^-1 respectively. The fluorescence of pyrene is strongly quenched by GMP, CMP, and TMP but only slightly by AMP. Fluorescence quenching analysis has yielded the values 87M^-1, 73 M^-1, and 154 M^-1 for the excited state association constants with GMP, CMP, and TMP, respectively. The corresponding values for the excited state second-order rate constant for complex formation are: 3.3 times 10⁹M^-1 s^-1 4.1 times 10⁹M^-1 s^-1, and 4.0 times 10⁹M^-1 s^-1. The probabilities of complex formation per collision between an excited pyrene molecule and a nucleotide are: 0.52, 0.64, and 0.63. The values for the excited state rate constant for dissociation of the complex are: 3.8 times 10⁷s^-1 5.6 times 10⁷s^-1, and 2.6 times 10⁷s^-1. The possibility is discussed that partial transfer of charge from pyrene to nucleotide may be playing a role in the complex formation process.     

Global fallout levels of <Superscript>99</Superscript>Tc and activity ratio of <Superscript>99</Superscript>Tc/<Superscript>137</Superscript>Cs in the Pacific Ocean

Summary Global fallout levels of ⁹⁹Tc and ¹³⁷Cs of surface seawater in the Pacific Ocean were measured. The ⁹⁹Tc concentrations ranged from 0.62 to 3.33 mBq^. m^-3and 5 of 6 samples showed less than 1 mBq^. m^-3except one sample taken in the Great Barrier Reef, Australia. The ¹³⁷Cs concentrations ranged from 2.13 to 3.14 Bq^. m^-3, showing a gradual decrease in the North Pacific toward the equator and a constant level in the South Pacific. The ⁹⁹Tc/¹³⁷Cs activity ratios ranged from 2.5^. 10^-4to 2.9^. 10^-4, which is very close to that calculated theoretically from the fission yield.     

Natural radioactivity distribution in geological matrices around Kaiga environment

Summary The activity and absorbed dose rate of the naturally occurring radionuclides, viz. ²³⁸U, ²³² Th and ⁴⁰K were determined in soil and rock samples collected around Kaiga site. The mean activity levels (Kaiga soil) of naturally occurring ²³² Th are comparable with that in worldwide soil, while concentrations of ²³⁸U and ⁴⁰K are lower than those in worldwide soil. The absorbed dose rate in outdoor air ranged 20-58 nGy ^. h^-1 with a mean of 33.3 nGy ^. h^-1, which is below the world average of 60 nGy ^. h^-1. The total effective dose rate in outdoor air for soils ranged 25.6-74.4 mSv ^. y^-1 with a mean of 43.0 mSv ^. y^-1. The estimated dose rate at Kaiga is comparable with that estimated at Kakrapar and Rawatbhata and much less than that estimated at coastal sites of India.     

A sequential repair model of photoreactivation in bacteria

Abstract— Kinetics of photoreactivation were studied in E. coli WP2 hcr^-, a strain deficient in dark repair. Cells in aqueous suspension were subjected to u.v.-irradiation, then exposed to photoreactivating light for different periods. Survival curves, with samples at a minimum of six u.v. doses, were obtained at several periods of photoreactivation ranging from zero to maximum. The surviving fractions do not conform to a dose-reduction model, but instead, they fit a ‘sequential repair’ model that assumes as a limiting condition that the number of active enzyme molecules is small. The model used assumed: (1) a single enzyme molecule is active at any one time; and (2) inactivating events are nullified consecutively around the DNA molecule. The mathematics of the model are derived and presented. Photoreactivation is attributed to the action of two processes. (1) A photochemical process, that is rate limiting below 1000 ergs mnr^-2 sec^-1, was measured at a photoreactivating irradiance of 60 ergs mm^-2 sec^-1. This has a rate constant of 5 × 10^-5‘events’ erg^-1 mm². (2) A dark process, measured at photoreactivating irradiances of 4000 and 6000 ergs mm^-2 sec^-1, has a rate constant of 2.2 ‘events’ min^-1.     

The photoperoxidation of unsaturated organic molecules--XV. O21Delta g quenching by bilirubin and biliverdin.

Abstract —The use of competitive methods with rubrene as reference acceptor provides values of the rate constants k^B_Q= 2.3 times 10⁹/ mol^-1 s^-1 and k^v_q= 3.3 times 10⁹ mol^-1 s^-1 for the physical quenching of O₂¹δg, by bilirubin (in CCl₄) and biliverdin (in CHCl₃) respectively attributed to electron and energy transfer processes. The rate constant k^B_R= 1.7 times 10⁸/ mol^-1 s^-1 for bilirubin reaction with O₂¹δg is considerably greater than that k^v_R 3 times 10⁸ mol^- s^-1 for the reaction of biliverdin which has identical O₂¹δa, acceptor sites, and is attributed to a primary Type I oxidation process followed by a slower Type II addition of O₂¹δg to the primary products.     

Determination of copper with neocuproine by thermal-lens spectrometry

Conditions for the spectrophotometric determination of copper with 2,9-dimethyl-l,10-phenan-throline (neocuproine) in the presence of ascorbic acid in a water-ethanol solution (9 : 1) at pH 4.5–5.0 have been found. The detection limit is 3 x 10^-6 M. The concentration range is from 4.4 x 10^-6 to 3 x 10^-4 M. Conditions for the determination of copper(I) with neocuproine by thermal lens spectrometry have been proposed. The detection limit is 4 x 10^-7 M. The concentration range is from 7 x 10^-7 to 6 x 10^-5 M. Iron(II) at concentrations as high asn x 10^-4 M does not interfere with the determination of copper. Changes in the conditions for the photometric reaction associated with passing from spectrophotometric measurements to thermal lensing are discussed.     

Theoretical exploration of structure-reactivity relationships in organometallic chemistry: butadiene insertion into the organyltransition-metal bond and conversion of the allyltransition-metal fragment in the [Ni(η-Cp)(η-phenyl)(η-butadiene)] complex

We have theoretically examined the reaction course of the butadiene insertion into the arylNi^II bond in the [Ni^II(η⁵-Cp)(η¹-phenyl)(η²-butadiene)] complex (1), by employing a gradient-corrected DFT method. Critical elementary processes have been scrutinized, viz. monomer insertion, rotational allylic isomerization and allylic η¹-σ→η³-π rearrangement. The first mechanism suggested by Lehmkuhl et al. was refined and supplemented with important details. The critical factors that determine the generation of anti-η³- and syn-η³-allyl isomers of the [Ni^II(η⁵-Cp)(1-benzyl-allyl)] product have been elucidated. This let us to rationalize the experimentally observed, almost exclusive formation of the anti-η³-allyl isomer. Butadiene preferably inserts in η²-mode into the η¹-phenylNi^II bond, initially giving rise to the η¹(C³)-allyl product species, 3σ. The direct formation of the η³-allyl product species, 3π, along the alternative path for η⁴-butadiene insertion, however, is found to be almost entirely disabled kinetically. The thermodynamically favorable η²-trans form of 1 is also shown to be more reactive in accomplishing CC bond formation. Species 3σ is indicated to be a metastable intermediate, occurring in an appreciable stationary concentration. Its respective anti and syn isomeric forms are likely to be in equilibrium, due to the facile rotational isomerization. The subsequent allylic rearrangement into the thermodynamically strongly favorable η³-allylNi^II coordination mode is shown to be the crucial elementary step that discriminates which of the isomeric η³-allyl forms is preferably generated. The higher reactivity of the anti isomer in this process decisively determines the almost exclusive formation of the anti-η³-allyl product species under kinetic control. The requirement of elevated temperatures for the anti-η³-allyl→syn-η³-allyl isomerization to occur, as revealed from experiment, is attributed to the pronounced thermodynamic stability of the η³-allylNi^II coordination.     

Einbauversuche mit (3H und 14C)-doppelmarkiertem Farnesol in Cantharidin. 5. Mitteilung zur Biosynthese des Cantharidins

Incorporation experiments with (³H and ¹⁴C) doubly labelled farnesols into cantharidin After injection of 11′, 12-[³H]-7-[¹⁴C]-farnesol or 11′, 12-[³H]-5,6-[¹⁴C]-farnesol, the ³H-label is located specifically in the C(9)-methyl-group of cantharidin, whereas the ¹⁴C-labelling pattern follows an incorporation via acetic acid (Scheme 4). C-Atoms 5, 6 and 7 from the middle part of the farnesol molecule are utilized for cantharidin biosynthesis to an extent that is about 2.1–11% of the incorporation rate of the methyl groups C(11′) and C(12), depending on the position of the ¹⁴C-label in farnesol. These results confirm our earlier hypothesis [1] that the C₁₀-molecule cantharidin is biosynthesized from the C₁₅-precursor farnesol which is cleaved between C(1)–C(2), C(4)–C(5), and C(7)–C(8). The synthesis of 7-[¹⁴C]-farnesol and of 5,6-[¹⁴C]-farnesol is described.     

STEREOELECTRONIC PROPERTIES OF PHOTOSYNTHETIC AND RELATED SYSTEMS—VII. AB INITIO QUANTUM MECHANICAL CHARACTERIZATION OF THE ELECTRONIC STRUCTURE AND SPECTRA OF CHLOROPHYLLIDE a AND BACTERIOCHLOROPHYLLIDE a CATION RADICALS

Abstract— Ab initio configuration interaction wavefunctions and energies are reported for 29 doublet states and three quartet states of the cation radicals of ethyl chlorophyllide a (Et-Chl a⁺) and ethyl bacteriochlorophyllide a (Et-BChl a⁺). In Et-Chl a.⁺ I the lowest excited doublet state D₁ is estimated to lie 5220 cm^-1 above the ground state D₀, with a negligibly small D₁← D₀ transition probability. The lowest quartet state, Q₁, is estimated to lie 7980 cm^-1 above D₁. The absorption spectrum up to 20,000cm^-1 is shown to consist primarily of numerous low-intensity ‘background’ transitions, with transitions to D₅ and D₁₁ accounting for the observed peaks at 12,200cm^-1 and 17,500cm^-1, respectively. The large intense band at 25,000cm^-1 is due primarily to transitions to D₂₂ and D₂₃, with numerous lower-intensity transitions to neighboring states. In Et-BChl a.⁺ D₁ is estimated to lie 7112 cm-¹ above D₀, and Q, is approximately 5725 cm^-1 above D. A pair of states, D₃ and D₅, account for the absorption at 11,000 cm^-1, while another pair of states, D₁₃ and D₁₄, are associated with the broad, weak absorption near 20,000 cm^-1. The two prominent intense peaks at 23,700 cm^-1 and 27,700 cm^-1 are assigned to D₂₃ and D₂₈, respectively, while the shoulder located at 25,500cm^-1 is attributed to transitions to D₂₄ and D₂₆. As in Et-Chl at, numerous background transitions are found throughout the spectrum. The π spin density distribution in D₀ of both molecules is similar, with spin density found predominantly on the α-carbon atoms. In both systems, approximately 65% of the π spin density in D₁ is found on the methine carbon atoms, with the remainder found largely on the nitrogen atoms.