No description available.

The relative yields of 19 nuclides* have been measured in the 14-MeV neutron-induced fission of natural uranium, and have been shown to fall on the familiar type of double- peaked mass-yield curve. The measurements on the two xenon isotopes ((^133)Xe and (^135)Xe) indicate the presence of fine structure in the region of the heavy peak. The mean peak-to-trough ratio is 9.1, which is of the order expected for fission at this energy, and the best fit for the mirror-points is obtained when v, the number of prompt neutrons emitted per fission, is taken to be 4. The condition that the sum of the yields of all the fission-products must be 200% enables values for the absolute yields to be determined: the value so obtained for (^99)Mo is (6.31 ± 0.23)%. A Cockcroft-Walton accelerator was used to produce the 14-MeV neutrons by the D+T reaction. At this neutron energy the cross-sections for (^235)U and (^238)U are of the same order of magnitude, so the results are essentially those for the fission of (^238)U.

The first part of the work described in this thesis deals with the preparation of uniformly thin sources suitable for the counting of weak β-emitting radioisotopes. The method developed involved the preparation of a thin sulphonated polystyrene layer supported on a thin VYNS film on which cations were deposited by ion-exchange. The p-counting efficiency of the sources in a 4 II β-proportional counter was determined by coincidence counting. Autoradiography was used to determine the uniformity of the sources. Evaporated gold on the VYNS film support was found to promote the surface diffusion of mercury and investigations led to a procedure applicable to the measurement of the counting efficiency of p-emitting mercury isotopes; a method for the calibration of a proportional counter used in the determination of the Tl(^203)(n,pHg(^203) cross-section was thereby evolved. In Part II preliminary experiments were directed towards finding a suitable "liquid ion exchanger" for an investigation of ion-exchange behaviour, particularly at high electrolyte concentrations; mono-(2-ethylhexyl) phosphoric acid (H(_2)MEHP) in toluene was eventually selected.

No description available.

The photoluminescence properties of cyclometallated second and third row transition metal complexes make them potential candidates for use in a range of applications such as triplet harvesting agents in OLEDS, as photosensitizers, and in solar cells. Also, the strong luminescence of these complexes gives them much potential for use in chemosensing applications and as bioimaging agents. This final topic is an area of increasing study as a result of the diverse and tuneable excited states of such molecules, and their advantages over conventional organic emitters such as reduced photobleaching and long luminescence lifetimes allowing time-resolved imaging to be performed. The synthesis of cyclometallated complexes of the type [Pt(N^C^N)Cl], [Ir(N^C)2(L)Cl], and [Ir(N^C^N)(N^X)Cl]n+ (where N^C^N and N^C are terdentate and bidentate cyclometallating aromatic ligands; L = monodentate pyridine ligand; X = heterocyclic N or cyclometallated aryl C; n = 0,1) is described and their reactions with thiolates are explored with the aim of producing new classes of thiol sensors. Thus, novel monometallic complexes of the type [Pt(N^C^N)(thiolate)] and [Ir(N^C^N)(N^C)(thiolate)] are reported as well as a novel series of dimers with the general structure [Ir(N^C)2(μ- thiolate)]2 and one example of a [Ir(N^C^N)(μ-thiolate)(thiolate)]2 dimer. The effect of the introduction of a thiolate ligand on the excited states of the Pt(N^C^N) complexes is also described. In addition, a series of luminescent compounds based on the dansyl group or iridium complexes are reported for use as bioimaging agents and their utility in cellular assays has been investigated. These probes incorporate molecular structures inspired by the ability of small molecules to mimic the activity of certain redox active proteins and hence have the potential to engage in disulfide exchange processes in vivo. These compounds have been shown to display acceptable uptake into cells without excessive cytotoxicity and have been used to obtain fluorescence microscopy images of live CHO cells.

No description available.

A radiochemical study has been made of complex formation in aqueous solutions containing trivalent lanthanide and actinide metal ions and selected ligands. Partition methods using a cation-exchanger and a liquid extractant (di(2-ethyIhexyl)phosphoric acid [HY](_2), in toluene) as the second phase were developed and measurements carried out with La, Ce, Eu, Gd, Am and Cm with one or more of the ligands, a-hydroxy-isohutyrate, fluoride, sulphate and oxalate. The isotopes La(^140), Ce(^144)/Pr(^144), Eui(^152), Gd(^153) and Am(^241) were used in conjunction with conventional methods of measurement of β- and ϒ-emitters. Liquid-scintillation counting procedures were developed for the measurement of the α-activity from Cm(^244). It was found that in the presence of a constant and representative concentration of each of the ligands used only M(HY(_2))(_3); extracts into the toluene phase and metal ion complexed by the ligands concerned does not partition. A cation-exchange resin on the other hand is known to take up partially complexed species in addition to 'free' metal ions. A method was evolved whereby data obtained separately by the ion-exchange and solvent- extraction methods could be used to calculate distribution coefficients of partially complexed species partitioning into the resin phase. The results showed that residual cation charge as well as the size of the exchanging species are important in determining the extent to which ion-exchange partition occurs. It was also found that the Pronaeus' method of treatment of ion-exchange data where more than two ligands are attached to a metal ion may be Inadequate and that assumptions frequently necessary regarding the distribution coefficient of partially complexed species may be considerably in error depending on the ligand. The investigations carried out in this work have indicated the application of HDEHP to the determination of equilibrium constants particularly of α-emitting higher actinides and in studies where more than two complexes are formed. Equilibrium constants for the complexes formed were computed and various tests applied to the method of computation from ion-exchange distribution data. Equilibrium constants obtained are generally in good agreement with relevant published data.

A study has been made of the application of N-benzoyl-N-phenylhydroxylamine (NBPHA) to separations of a number of transition and main group elements by liquid-liquid extraction methods. In general the partition of each element from aqueous hydrochloric or perchloric acid has been examined as a function of acidity, reagent concentration in chloroform (the second phase), rate of extraction and range of metal ion concentration. Where extraction occurred only at low hydrogen ion concentrations an aqueous acetate buffer was employed. Back-extraction into aqueous phases of various compositions was also investigated. Niobium is thus separated from zirconium; niobium, tantalum, protactinium from each other; protactinium from uranium, thorium and its fission products and gallium, indium, thallium, germanium, tin and lead from each other, A comparative study of KBPHA and the ammonium salt of N-nitroso-phenylhydroxylamine (cupferron) in the extraction of tin, antimony, arsenic and bismuth has also been carried out and potential separations with NBPHA noted. Depending on the valency state of tin, cupferron gives two distinct products, while NBPHA gives only a single product in which the valency state of the tin has previously been in some doubt. Partition studies have been devised to examine the dependence of extraction on reagent, chloride ion (a constituent of the product precipitated from hydrochloric acid) and hydrogen ion concentrations. The results in combination with those from infra-red and nuclear magnetic resonance examinations of the product of precipitation show that the substance extracted from 1 M hydrochloric acid is the same as that obtained by precipitation under similar conditions. It is Sn(C(_13)H(_10)O(_2)N)(_2)Cl(_2) which contains tin-(IV). Decomposition products of cupferron were examined using vapour phase chromatographic methods. Some polarographic work on the behaviour of tin and antimony in the presence of KBPHA has been carried out. Methods for the determination of these two elements in mixtures are presented using NBPHA.

No description available.

The relative yields of 14 mass chains in the fission of thorium by 14 MeV neutrons have been measured radio- chemically. Fission-product sources were counted with an end-window β-proportional counter which was- absolutely calibrated for as many of the nuclides measured as was, practicable. The measured relative yields were corrected to total chain yields on application of the equal charge displacement hypothesis, and a mass-yield curve produced with two narrow peaks and a broad trough. Peak maxima occur at mass numbers 91 and 137.4, with a peak width at half-height of 12.5 mass units. The occurrence of a subsidiary maximum in the centre of the trough is considered, although insufficient evidence is, available to delineate this completely. The relative yields were converted to absolute yields on imposition of the condition that the sum of the yields of all the fission-products must be 200%. The value obtained, for the absolute yield of mass number 91 is 6.48 + 0.33?%. *Mass Numbers: 83, 84, 91, 93, 97, 99, 105, 111, 112, 113, 129, 132, 139, 143.