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The surface reactivity of thorium, uranium, neptunium and americium has been investigated under UHV conditions using X-ray photoelectron spectroscopy (XPS) and ultra violet photoelectron spectroscopy (UPS). Oxygen, nitric oxide, nitrogen dioxide and nitrous oxide adsorption on a polycrystalline thorium surface has been investigated at 298 K. 02 dissociatively adsorbs on the surface resulting in the growth of Th02. All three of the nitrogen oxides adsorb dissociatively with both oxygen and nitrogen adsorbed on the thorium surface. The formation of thorium oxynitride (ThOxNy) is proposed. Reaction of NO, NO2 and N20 with a polycrystalline uranium surface has also been investigated at 298 K. N2O adsorbs dissociatively leaving only oxygen adsorbed on the uranium surface. NO and N2O also adsorb dissociatively but in these cases both oxygen and nitrogen remain on the surface. The formation of uranium oxynitride (UOxNy) is proposed. For exposures >350 L the rate of reaction of NO with the oxynitride surface decreases significantly. In contrast, NO2 continues to react with the surface and a further increase in surface oxygen concentration is observed. Adsorption of O2, NO and CO on thin films of neptunium metal has been studied at 80 and 300K. Following exposure to 02 at 80 and 300K, an intermediate surface oxide of Np is formed which is unstable with respect to the formation of Np02. This intermediate oxide is proposed to be associated with the chemisorption phase, NpO(chem). Dissociative adsorption of CO and NO is observed at 80 and 300K. A surface oxidic compound is formed which is not a simple neptunium oxide. NpO(chem) states are proposed to be stabilized by the presence of carbon/nitrogen as neptunium oxycarbide and oxynitride respectively. The interaction of O2 and NO with americium thin films has also been investigated. The formation of A1TI2O3 is proposed and it was found that it is not thermodynamically viable to produce a higher oxidation state of americium via gas dosing (at 300 K under UHV). Adsorption of NO on the surface results in the dissociative adsorption of N and O, and in the formation of a surface compound.

A range of new lanthanide complexes have been synthesised. The ligands and ligand precursors were characterised by NMR (1H, 13C), electrospray mass spectrometry, UV-Vis and IR spectroscopy. Several ligands or ligand precursors have been crystallised and analysed by X-ray crystal diffraction. The complexes were characterised by electrospray mass spectrometry, UV-Vis, IR spectroscopy and luminescence spectroscopy. In Chapter 2 a quinoxaline chromophore was incorporated in a macrocyclic ligand and it was shown that quinoxaline was capable of sensitising Ln(III) luminescence in the visible and NIR region. The Eu(uT) emission intensity and lifetime were shown to be responsive to pH. In Chapter 3 two N-(2-nitrophenyl)acetamide-derived chromophores were incorporated into macrocyclic ligands and shown to be capable of sensitising Ln(III) emission. A combined structural, spectroscopy and computation study was undertaken to investigate the spectral differences between the ligands. In Chapter 4 a synthetic strategy towards the synthesis of metal-ion responsive lanthanide complexes is detailed. The Eu(III) complexes were titrated against various metals and it was shown that the metal-based luminescence was sensitive to the concentration of Hg(II) and Cu(II). Hydroxyquinoline, aminoanthracene, amidopyrene, amidoquinoline and amidoanthraquinone chromophores were incorporated into macrocyclic ligands in Chapter 5 in order investigate the feasibility of adapting the synthetic strategy presented in Chapter 4 to synthesise responsive probes containing long-wavelength absorbing chromophores. Binding studies demonstrated the potential for these complexes to respond to the presence of Group 12 metals with changes in the overall emission intensity, relative intensity of hyperfine transitions and luminescence lifetimes. In Chapter 6 the synthetic strategy presented Chapter 4 was utilised to synthesis a ligand capable of forming bimetallic complexes with Ln(III) ions. Combined luminescence and relaxivity studies indicated that the binding of Hg(II) resulted in a change in Ln(III) coordination environment, whereas the binding of Cu(II) caused quenching of emission without increasing q.

However, some differences are observed and further investigation is required to understand fully the nature of these differences on the atomic scale.

The investigations described in this thesis relate to the development of an accurate method for the comparison of strengths of weak neutron sources with different spectra. This is part of a programme for the establishment of an absolute neutron standard. A detailed review of the preparation and properties of various portable neutron sources at present in use has been presented. The advantages of the stoichiometric compound, Radium Beryllium Fluoride (RaBeP4 ), as a reproducible neutron standard have been discussed. A survey of the existing methods for the absolute and relative strengths of neutron sources has been made and the need for an accurate method for the comparison of strengths of weak neutron sources with different spectra has been pointed out. The principle of thermalisation followed by physical integration, with a solution of indium sulphate, has been employed for developing a new method for the measurements of relative neutron source strengths. Using this method, the relative strength of the proposed RaBeF 4 standard source with respect to a standard radium-I--beryllium source was determined with an accuracy better than 1%. When the absolute strength of the latter source is determined, the absolute strength of the RaBeF4 source can be given with this accuracy. Investigations were also carried out to estimate the extent of loss of fast neutrons from the radium-(-beryllium sources by reactions with oxygen and sulphur present in aqueous moderator solutions normally used for neutron strength comparisons. The principle involved was to compare the relative strengths in an aqueous medium and an organic medium containing less oxygen, but having the seine hydrogen and indium contents. Since no systematic errors are involved, the value obtained is considered more reliable.

The investigations recorded in this thesis relate to a radiochemical study of the fates of iodine atoms recoiling after undergoing radiative neutron capture. Particular attention has been focussed upon mixtures of alkyl iodides, using the 'quasi-stable' fission product (^129)I (1.72 X l0(^7) y) to fix unequivocally the origin of the recoil iodine found in the products. Techniques have been developed for the synthesis of methyl and propyl iodides labelled with (^129)I on a micro-scale, and mixtures of these with unlabelled alkyl iodides have been irradiated in the Harwell reactor "BEPO". Other irradiations have been made with 14 MeV neutrons from the D+T reaction; with a Ra-ɤ-Be neutron source; and with a 100 curie (^60)Co source. Separation (by gas/liquid chromatography) and measurement techniques have also been perfected. From a study of the distribution of the active iodine between methyl and propyl iodides it seems that the recoiling atom is more likely to appear as methyl than as propyl iodide. In the case of (^130)I recoils this, ratio is about 3:1, for (^128)I it is about 1.8:1 and for (^126)I (produced by n,2n reaction) it is about 2.2:1. The results can only be explained if it is also assumed that about 10% of the neutron captures (in (^129)I) either do not result in bond rupture or lead to an immediate recombination with the residue of the parent molecule. The effect of ɤ-radiation (unavoidably present in neutron irradiations) on the exchange of iodine between methyl and propyl iodides, has been studied with the aid of (^131)I, using a 100 curie (^60)Co source.

The relative yields of 8 mass chains both in the fission of Th(^232) y 3- and 14-Mev. neutrons have been easured radiochemically. The measured relative yields ere corrected to total chain yields by applying the equal charge displacement hypothesis. The relative yields were converted to absolute yields by imposing the condition that the sum of all the fission products must be 200%. Use has been made of the measured relative yields of near complementary fragments to determine the number of secondary neutrons emitted by a few fragment pairs. The number of secondary neutrons emitted by mass number 145 and its complementary fragment in 14-Mev neutron fission was found to be 4.04 and by mass number 132 and its complementary fragment in 3-Mev neutron fission to be 2.30.The mass, yield curves obtained in the present investigations showed the predominance of asymmetric fission at the lower excitation energy. The maxima of the peaks for 14-Mev fission were at mass numbers 91.00 and 137.96, while those for 3-Mev neutron fission were at mass numbers 91.55 and 139.28. An explanation of the relative change of the peak maxima at different energies has been put forward.