Studies Using Separated Isotopes

2 PVT Isotope Effects for Liquids, Vapors, and VPIE at LV Equilibrium 

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A number of other reactions have been studied using orthodox isotopic tracer techniques for which complete exchange in the time of separation was observed. The lower limits for the specific rates that can be calculated are considerably smaller than those to which we have referred, and since in many cases no proof could be adduced that the separation method did not cause the exchange, these results are not reported. The review by Amphlett (5) gives references to many of the literature reports on these and other reactions in the entire field. 

MeV. It has a half-life of 34 5 s and decays with 67% by emission of two sequential a particles via Lr T1/2 = 4.4 s) to the long-lived Ti/2 =28 min). In addition, Db shows spontaneous fission with a decay branch of 33% possibly from the short-lived EC-decay daughter Rf. Hence, identification of each separated labeled molecule is based on either detection of two characteristic a-particles and their lifetimes or on the detection of a spontaneous fission decay. A more recent chemical study used the isotope Db formed in the reaction Am( e, 5n) Db at a beam energy of about 120 MeV [23]. Db has a half-life... 

It is a simple matter to determine the forward (exothermic) and reverse (endothermic) rate coefficients, and for such reactions using the SIFT technique (ideally suited for such studies because separate isotopic ions can be injected and the reaction temperature can be accurately controlled even down to 80 K). For reactions [16] it is observed that increasingly exceeds as the temperature is reduced. This is because the reverse reaction is endothermic by 39.8 meV (3.84 kj mol ), by virtue of the zero-point-energy difference between H2 and HD, and the ionization energies of H and D differ by 4 meV (0.38 kJ mol" ). Hence in cold ISC the reverse reaction is effectively stopped whilst the forward reaction proceeds at the gas kinetic rate. This effectively ensures that much of the deuterium in dense interstellar... 

Barker and Kahn have made a detailed study of the exchange in carbon tetrachloride media using the isotope " Sb to label the Sb(III) species. The reaction was carried out in sealed ampoules covered with A1 foil in the presence of an atmosphere of He or Ar gas. The separation method used involved complexing the Sb(V) with fluoride (brought about by addition of ethanol, HCl and HF) followed by precipitation of the Sb(III) with H2S and finally addition of boric acid and HCl, removal of the CCI4, and treatment with H2S to remove the Sb(V). Zero-time exchange was 5 %. 

Anderson and Bonner made the first detailed kinetic study on the exchange using the isotopic method ( Cr) and a separation method based on the conversion of Cr(II) into Cr(IIl) oxalate and an ion-exchange treatment. To prevent oxidation of Cr(II) during exchange a hydrogen atmosphere was maintained over the reaction mixture. The rate law found to be obeyed for the concentration ratio range Cr(III)/Cr(II) of between 3.3 x 10 and 2.0 in perchlorate media was... 

Carbon-13 relaxation depends predominantly on intramolecular contributions, whereas proton relaxation is sensitive to inter-molecular as well as intramolecular interactions. However, by use of isotope dilution— the two types of interactions may be separated. Studies utilizing both nuclei can thus yield complimentary information. 

Aston, with experience in chemistry as well as physics, began working at the Cavendish Laboratory in 1909 on separating isotopes using mass spectrography. He started to assist Thomson in his study on positive rays. Together they improved on Thomson s original apparatus. 

A multiple ion collector device is required for the simultaneous determination of separated ion beams in precise and accurate isotope ratio measurements in order to study, for example, isotope fine variation in Nature or during tracer experiments using enriched stable isotope tracers. In thermal ionization mass spectrometers or in ICP-MS, mostly a system of several Faraday cups (up to 16) and/or ion counters (electron multipliers) is applied. In the photographs in Figures 4.7 and 4.8 examples of multiple ion collector systems are shown from the mass spectrometers MC-ICP-MS... 

HEVESY, GEORG de (1885-1966). A Hungarian chemist who won the Nobel prize in chemistry in 1943, for his work on (he use of isotopes as tracers in the study of chemical processes. He discovered the element hafnium in 192.7. One of his interesting projects involved the calculation of ihc percentages of chemical elements in the universe. He also was involved in research using radioactive lead and phosphorus traces. His work included the separation of isotopes by physical means. His Ph D was granted ai Freiburg in 1908. 

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