摘要:

Spatial and temporal variations of δD and δ18O in mean monthly precipitation and groundwater are described by means of a simple water vapour advection model, which links the isotope data to the vertically integrated horizontal flow of vapour. This model yields a temperature dependence of the isotope precipitation data, which is compared with the experimental temperature effect. Short-term variations of δD and δ18O in mean daily water vapour reflect the varying influence of different air masses on the local weather. A spectral analysis of these short-term variations yields predominant periodicities of about 10, 20 and 30 days, which are related to the long-wave pattern of the zonal drift in the upper troposphere. δD and δ18O in plant material (tree rings, peat), solids, lake sediments, speleothems and in other carbonates of paleoclimatic interest is primarily influenced by the isotopic composition of local precipitation, atmospheric moisture and by temperature dependent isotope fractionation. The relevance of such fossil material (peleowaters included) fo paleoclimate and in particular for the reconstruction of the water vapour circulation pattern in the past is discussed.

ISSN:0021-1915    

DOI:10.1080/10256018508623487

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Formulae are given for thermodynamic isotope effects of simple fluids. These fluids are here treated as hard-sphere and square-well systems. A special method, the micropotential method, is used for the calculation oj classical thermodynamic functions. Quantum corrections to these functions are also given. Isotope effects due to the variation of the total mass (mass effects) are related to the estimation of quantum corrections of thermodynamic functions. Isotope effects due to the variation of potential parameters (potential effects) are calculated for methane. The potential effects of methnne are of the same order of magnitude as the corresponding mass effects.

ISSN:0021-1915    

DOI:10.1080/10256018508623488

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Influences of operating temperatures and concentrations of feed boric acid solutions were examined on the above titled process over the ranges of 25–70°C and 0.1–1.6 mol/dm3(M), respectively. The ideal displacement chromatography with a very sharp-cut boundary of a boric acid adsorption band was realized at higher temperatures and lower boric acid concentrations within the experimental conditions. The isotope separation coefficient ɛ was found to decrease with increases in either temperature or the boric acid concentration. The observed values of ɛ at 25°C were 0.013, 0.012 and 0.011 depending on the feed boric acid concentrations of 0.1 M, 0.4 M and 0.8 M, respectively. The ɛ's at 70°C were determined as 0.0097 (0.1 M), 0.0086 (0.4 M), 0.0083 (0.8 M) and 0.0073 (1.6 M). The operational condition of temperature 40°C and 0.4 M of the boric acid concentration was proposed as the optimum for the production of enriched10B isotope by using the present process.

ISSN:0021-1915    

DOI:10.1080/10256018508623489

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The pulse radiolysis of hydroquinone solutions in the presence of a mixture of N2O and O2has shown that a transient species is formed by the addition of O2to the trihydroxycyclohexadienyl radical to form a peroxy radical. The G value for this radical is estimated to be ∼6.5 and the rate coefficient of its decay is found to be ∼2.7 × 107M−1s−1.

ISSN:0021-1915    

DOI:10.1080/10256018508623490

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The ability of crown-ethers for selective separation in a few cases is well known. Initial experiments were made to investigate the stability against gamma-irradiation. In tltese experiments l8-crown-6-ethers were used. Irradiation was carried out in the dose range from 5 kGy up to 1 MGy using a60Co-source. Radiolysis products were analyzed by gas chromatography andNMR-spectroscopy. It has been shown that crown-ethers can be used for separation steps in various radiochemical processes not only in a laboratory but also in a technical scale.

ISSN:0021-1915    

DOI:10.1080/10256018508623491

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Gamma radiolysis of aerated and deaerated solutions of di- and trivalent cobalt and 1,2-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (DCTA) was investigated. A radiolytic mechanism has been proposed and discussed. It has been shown that the degradation of the chelate is due to the OH radical while the oxidation of the divalent chelate to the trivalent chelate is due to H2O2.

ISSN:0021-1915    

DOI:10.1080/10256018508623492

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

For99mTc generator activities ranging from 74–92.5 GBq, an adsorbent consisting of a mixture of alumina and silica gel was modified by copper addition. The quantity of copper adsorbed on alumina was in the range of 10–15 mg Cu/g alumina. It was found that saline solution does not influence the performance of the columns. A high elution yield of99mTc and good quality of the eluate was obtained both for the “wet” and “dry” column.

ISSN:0021-1915    

DOI:10.1080/10256018508623493

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The effect of sterilisation of Al2O3(by radiation, thermal treatment and in the autoclave) on its adsorption capacity and efficiency of elution of99mTc has been investigated. No difference has been observed in the adsorption capacity of sterilised and unsterilised Al2O3samples. However, efficiency of elution of99mTc differed in sterilised and unsterilised samples, and even depended on the sterilisation procedure used. The highest elution efficiency was found with unsterilised Al2O3(94%), somewhat lower with thermally sterilised (90%) and the lowest with60Co gamma radiation sterilised Al2O3(85%). Al2O3sterilised at 300°C has slightly higher adsorption capacity with respect to molybdenum.

ISSN:0021-1915    

DOI:10.1080/10256018508623494

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Not only an increased supply of rawwood and woood residues in the form of chips, but also aspects concerning the economic use of material in the enterprises of the woodworking indstry make questions relating to the techniques and methods of measurement an issue of particular interest for specialists on behalf of their high accuracy. In order to elucidate practicable methods for this purpose investigations were carried through using commercial immersion probes, which function on the principle of scattered radiation, and enclosed γ sources operating on the principle of transmission in chips of various dimensions and origin. On the one hand the task consisted in the elaboration of calibration curves and in the collection of factors, which exert an influence on the accuracy of measurement, on the other.

ISSN:0021-1915    

DOI:10.1080/10256018508623495

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

ISSN:0021-1915    

DOI:10.1080/10256018508623496

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor