<p> Historically, the thermal photon inverse slope parameter has been interpreted as the thermalization temperature of the QGP. Observation of the thermal photon spectrum in nucleus-nucleus collisions at the ALICE and PHENIX experiments obtain the inverse slope parameter, but the obtained values are inconsistent with the thermalization temperature predicted by the hydrodynamic model. It has therefore been argued that the inverse slope parameter is not representative of the true QGP thermalization temperature because not all thermal photons are emitted at thermalization. This research will probe this assertion using an investigation of flow and nuclear suppression of thermal photons from ALICE Pb-Pb collisions at &radic;<i>s_NN</i> = 2.76 TeV and comparison to p-p data at &radic;<i>s_NN</i> = 2.76 TeV.</p>

The gamma-ray transitions from the states populated in ⁵⁶Fe, ⁷⁵As and ¹⁵⁶Gd by the decay of ⁵⁶Co, ⁷⁵Se and ¹⁵⁶Eu were investigated using six Ge(Li) detectors and an intrinsic Ge detector. Coincidence studies were undertaken with a Dual-Parameter Energy-Time Spectrometer employing a fast-plastic scintillator detector and two large volume Ge(Li) detectors. The energies and intensities of measured gamma-rays were determined. The lifetime of energy levels in the n sec. range belonging to ⁷⁵As and ¹⁵⁶Gd were measured. The level schemes were constructed; log ft values, transition multipolarities, spins and parities were deduced. Different shell-model calculations were discussed and compared with experimental results.

The purpose of the work was a study of autoionization phenomenon following nuclear beta^--decay. Three approaches have been adopted in this respect, first, a study of total internal ionization probability and internal ionization probability as a function of beta^--particle energy, using a coincidence technique between emitted electrons (beta^--particles + orbital electrons) and subsequent K X-rays. Two isotopes have been studied using this approach, thallium-204 and promethium-147, where measurements of internal ionization probabilities for K-electrons are presented and results are discussed in terms of available theoretical treatments on total internal ionization. A second approach was applied in the case of thallium-204 where the internal ionization probability for K-electrons is deduced by comparison of mercury K X-rays resulting from an electron capture process with lead K X-rays due to the studied phenomenon. The third approach was applied in a measurement on erbium-169 using the straight forward technique of comparing the 118 Kev gamma-ray transition with thulium K X-rays and cn upper limit for K-shell internal ionization probability has been estimated. Difficulties and drawbacks of the experiment have been discussed. The two solid state detectors used in this work were a lithium drifted silicon detector for electrons and lithium drifted germanium X-ray detector for photons.

The Doppler-broadening technique has been applied to positron annihilation studies in plastically deformed and annealed specimens of zinc, indium, cadmium, lead, gold, and silver in the temperature range down to 4.2 K. Annealing studies in metals deformed at room temperature or under liquid nitrogen provided information on recrystallisation and on the nature of defects produced by plastic deformation. It has been shown that the specific trapping rate of positrons by deformation-induced dislocations is temperature independent. The equilibrium measurements, which extended up to their melting points in well annealed samples (except for gold and silver), enabled us to compare the models proposed to take into account the intermediate temperature dependence of the line-shape parameter. Also the mono-vacancy formation energies could be determined. The model fittings to the annihilation gamma-ray peak, which consisted of a Gaussian and an inverted parabola convoluted with the instrumental resolution function, provided the probabilities of positron annihilation with core and conduction electrons in the deformed and annealed samples. The annihilation spectra were recorded with a high resolution Ge(Li) detector whose resolution at a count rate of 5000 cps was 1.15 keV for the 514 keV line in ⁸⁵Sr. Further results on the temperature dependence of the width parameters of the Gaussian and parabolic distributions which characterise the momentum distributions of the core and conduction electrons, respectively, are presented.

An investigation is undertaken into methods of fast modulation and detection of submillimetre radiation. Detection at room temperature was achieved with travelling wave antennae coupled to a crystal rectifier. Metal-oxide-metal and metal-oxide-semiconductor rectifying junctions were studied. Generation of submillimetre radiation was performed by means of a hydrogen cyanide laser, operating primarily at a wavelength of 337 mum. The investigation was motivated by a need for an increase in output power from the laser which requires a fast switch operative at submillimetre wavelengths. Evaluation of a Q-switching technique, utilizing the near coincidences between absorption features in various vapours and the 337 mum emission line of the HCN laser was made. Further investigations were carried out on the transient properties of the plasma that forms the active medium of a pulsed excited HCN laser. Shift of the resonance condition by means of an ancillary discharge is undertaken as a Q-switching technique. Magneto-optical modulation as an alternative switching technique was also studied. To this end, the temperature-dependence of the magneto optical constants of seven different rare-earth iron garnets were studied at a wavelength of 337 mum. The properties investigated include the Faraday rotation, absorption coefficient and the room temperature refractive index. The theory of the magneto-optical effects at microwave and optical frequencies is reviewed and extended into the sub-millimetre region. Effects of magnetic anisotropy are discussed.

The experimental process for measuring the elastic and inelastic differential cross-sections for the scattering of helium-3 ions from 148, 150, 152 and 154 Samarium isotopes at 53 MeV is described. These results complement the data taken with helium-3 on ¹⁴⁴Sm, and with protons and deuterons on all the even Samarium isotopes at the same energy. The properties of the Samarium isotopes permit a study of the sensitivity of optical and collective model analyses on nuclei, whose characteristics change from spherical and vibrational (A = 144) to the region of permanent deformation where the nucleus is rotational (A = 154). These data are used to investigate the isotopic dependence of the optical model, particularly the recent folding models where an effective two-body interaction is folded in with the nucleonic density distribution. The data are also used to test the nucleus-nucleus model or "double folding" model, where an effective interaction is first folded with the target density and then with the projectile density. The scattering of the incident projectiles, ³He, ⁴He, ¹²C and ¹⁶O, from Samarium isotopes is tested with this theory. The importance of using an effective interaction with the correct "saturation" properties is also shown. D.W.B.A. and S.C.A. analyses of the data are performed, and the need for coupling low lying states to the elastic scattering is shown.

The carbon-13, tin-119 and deuterium MR spectra of a number of organo tin compounds have been detected by direct observation. The compounds fall into two main classes consisting of organo tin hydrides and organo tin chlorides. Tin-119 spin-lattice relaxation data for and nBu.Sn were measured, the first three over a temperature range. Measurements of tin-119 values were carried out with proton decoupling using, the inversion-recovery technique. NOE factors were measured by comparing spectra resulting from continuous and gated proton decoupling. For the n-alkyl tin compounds the T1 and HOE data indicated contributions to the total rate arising from the dipole-dipole interactions of tin-119 with remote protons. The competing mechanism was spin-rotation. T1 values were typically less than 5 seconds. Measurements of tin-119 T1 values in the hydrides were complicated by the magnitude of ( >1500 Hz) and only for nBuuSnH and Ph SnH have T and HOE factors n been determined. Carbon-13 T measurements have been made for factors have been determined for the last four molecules. Segmental motion was apparent in the n-alkyl chains. For rotation of the phenyl groups about the tin-carbon bond was indicated and the ratio of D /D has been determined.2The spin-lattice relaxation time of over a range of temperature was measured and the quadrupole coupling ponstant of deuterium in the bond was estimated as 88 +/- 10 kHz. The variation of the tin-119 chemical shift of with temperature and concentration has been investigated and the data can be adequately explained in terms of monomer-dimer equilibrium. Equilibrium constants and the enthalpy for the dissociation of the dimer have been evaluated. The tin-119 T1 and NOE data for this molecule at 1.4 and 2.3 T indicated a significant contribution to the relaxation from a field dependent mechanism.

<p> A study of ground state binding energy values listed in the Atomic Mass Evaluation 2012 (AME2012) using an interpretive approach, as opposed to the exploratory methods of previous models, is presented. This model is based on a postulate requiring all protons to pair with available neutrons to form bound alpha clusters as the ground state for an <i>N = Z</i> core upon which excess neutrons are added. For each core, the trend of the binding energy as a function of excess neutrons in the isotopic chain can be fit with a three-term quadratic function. The quadratic parameter reveals a smooth decaying exponential function. By re-envisioning the determination of mass excess, the constant-term fit parameters, representing <i>N = Z</i> nuclei, reveal a near-symmetry around <i>Z</i> = 50. The linear fit parameters exhibit trends which are linear functions of core size. A neutron drip-line prediction is compared against current models. By considering the possibility of an alpha-cluster core, a new ground-state structure grouping scheme is presented; nucleon-nucleon pairing is shown to have a greater role in level filling. This model, referred to as the Alpha-Deuteron-Neutron Model, yields promising first results when considering root-mean-square variances from the AME2012.</p><p> The beta-decay of the neutron-rich isotope ⁷⁴Cu has been studied using three high-purity Germanium clover detectors at the Holifield Radioactive Ion Beam Facility at Oak Ridge National Laboratory. A high-resolution mass separator greatly improved the purity of the ⁷⁴Cu beam by removing isobaric contaminants, thus allowing decay through its isobar chain to the stable ⁷⁴Ge at the center of the LeRIBSS detector array without any decay chain member dominating. Using coincidence gating techniques, 121 gamma-rays associated with ⁷⁴Cu were isolated from the collective singles spectrum. Eighty-seven of these were placed in an expanded level scheme, and updated beta-feeding level intensities and log(<i> ft</i>) values are presented based on multiple newly-placed excited states up to 6.8 MeV. The progression of simulated Total Absorption gamma-ray Spectroscopy (TAGS) based on known levels and beta feeding values from previous measurements to this evaluation are presented and demonstrate the need for a TAGS measurement of this isotope to gain a more complete understanding of its decay scheme. </p>

The object of this work was first to investigate, by the ionization method the dependence on the wall material of the ionization produced within chambers by high voltage-radiations of wave lengths from 0.013 A.U. to 0.5 A.U. The ionization chambers were pressed from mixtures of bakelite powder and graphite powder either with vanadium or cerium oxide. Secondly to investigate the possibility of measuring the quality of radiation by means of the ratio of ionizations in two chambers one of them is air walled and the other of higher atomic number. A study was also made of the validity of Gray's theory for calculating the ratio of ionization in such small chambers. The results of these investigations have shown that: I- Chambers moulded from the above mentioned mixtures are satisfactory electrical conductors and behave consistently in their interactions with the radiations used. The method may be useful in examining the quality of the scattered radiations from harder beams of X-rays generated at say between 400 and 1000 KV. The ratio of ionisation calculated according to Gray's theory agrees with the experimental one up to a wave length of 0.08A.U. The effective wave lengths of the X-ray beams were obtained from the complete spectral distribution of the energy and from measurement of the half value layers of the beams. It was found that in most cases it is sufficiently accurate, when considering the calculation of the ratio of ionizations in two chambers, to regard the beam as having that effective wave length corresponding to its half value layer.

This experimental and theoretical study aims at further investigation, by means of an extrapolation type of ionization chamber, of the ionization measurement of energy absorption from high-voltage radiations within a medium. Wavelengths ranging between 0.08 and 0.5 A0 were used. The walls of the ionization chamber were made of simple elements (graphite, aluminium and copper) or pressed bakelite - graphite mixtures which were loaded with cerium oxide in order to control the effective atomic number of the mixtures. A distinct advantage of the experimental arrangement used is the possibility of measuring the ionization per unit spacing when the air space is vanishingly small which thus eliminates the variable effects of chamber size. The results of earlier workers with chambers of fixed finite dimensions have been difficult to interpret in terms of theoretical considerations because of these effects. Furthermore, by varying the thickness of the upper plane electrode of the chamber, correction could be made for absorption of radiation in this electrode, which, at long wavelengths, maybe considerable in the media of higher atomic number. The results obtained with a chamber of graphite walls show that graphite behaves approximately as air walled material, the ionization per unit volume is constant i.e. the ionization I0 being proportional to V where V is the air volume. With walls of atomic number greater than that of air the ionization per unit spacing increases slightly as the spacing decreases up to a certain threshold spacing blow which it increases very rapidly. The ionization per unit spacing and the threshold spacing both depends upon the material of the electrodes and the wavelength of the radiation. The ionization per unit spacing at zero dimensions may be measured in two ways. Firstly, by drawing at the origin a tangent to the ionization - spacing curve and secondly by extrapolation to zero dimensions of the ionization per unit spacing - spacing curve. It was thus possible to compare these experimental observations with expectations based upon the Bragg -Gray theory of ionization within a cavity. This comparison suggests that the Bragg - Gray theory may be regarded as a satisfactory description of the facts for the range of wavelengths studied, at least for elements of atomic number up to that of aluminium (Z = 13). For copper (Z = 29) and the mixtures (depending upon the electron emission from Ce of Z = 58) the experimental results disagree with the theory except for the shortest wavelengths, and the disagreement increases with increase of wavelength. Suggestions are advanced and a modification made to Gray's equation in an attempt to correct for this disagreement. These are based upon a consideration of the sources and the energy of the photoelectrons omitted from the wall materials.