The reaction 15 O(alpha; gamma) 19 Ne is one of the potential break­out reactions from the Hot CNO cycle to the rp­process. As such, it may play an important role in nuclear astrophysics for the understanding of energy generation rates and the synthesis of proton­rich nuclei in sites of explosive hydrogen burning, such as novae and X­ray bursters. Experiments were performed at the radioactive ion beam facility, at Louvain­la­Neuve, Belgium, to test the validity of measuring indirectly the 15 O(alpha; gamma) 19 Ne reaction rate. The method utilised was the population of ex­ cited states in 19 Ne and the observation of their ff­decay. Information on the alpha branching ratios of the states of astrophysical interest, just above the alpha­ threshold, allows the reaction rate to be calculated, provided other resonance properties, i.e. T , ER and J , are known. Excited states in 19 Ne were populated via an inverse 18 Ne(d,p) reac­ tion on a deuterated polyethylene target. The reaction and decay products were measured in an experimental set up that comprised three silicon strip detector arrays, with a total of 320 detector elements. Two experiments were performed at E lab = 44.1 MeV and E lab = 54.3 MeV. The recoiling protons tagged the populated state and the detection of a coincident ff­particle and heavy residue pair identified its decay. Branching ratios for several states in 19 Ne were determined, showing the viability of this experimental approach. Optical model parameters were de­ termined from 18 Ne elastic scattering on deuterons. DWBA calculations were performed and compared with experimental angular distributions to yield spectroscopic factors. The results were comparable with a previous meas­ urement using a stable beam, despite the significantly lower beam intensity, and indicated that, provided the necessary beam intensity was available, this method would allow the measurement of the alpha branching ratio of the reson­ ance of most astrophysical interest at 504 keV and thus the determination of the 15 O(alpha; gamma) 19 Ne reaction rate.

It is now largely accepted that dark matter, and more specifically, Weakly Interacting Massive Particles (WIMPs), constitute the majority of the mass in our Universe. Within this thesis are presented: (i) an overview of the motivation and evidence for the existence of dark matter; (ii) a detailed discussion of direct detection techniques and a worldwide review of WIMP search experiments; and (iii) new experimental measurements and complementary detailed numerical simulations, carried out by the author, to determine the performance of DRIFT experimental technology. Collectively, this work explores the capability of DRIFT technology to detect dark matter, and in doing so, to resolve one of the key open questions of contemporary science. The DRIFT programme consists of an array of direct dark matter search detectors located in the Boulby mine. An important limitation to the experiment is the neutron and gamma-ray background. Experimental work presented here has determined the U and Th content of the cavern rock to be 66±6 ppb and 145±13 ppb respectively, clarifying ambiguities in previous estimations. Through the use of a Monte Carlo simulation the neutron and gamma-ray background experienced by DRIFT has been determined and the experimental implications assessed. In addition, the activity of the main neutron calibration source used to calibrate DRIFT modules has been measured and was found to be 11600 n s−1±5% on the date of exposure, resolving an earlier discrepancy. Analysis of experimental data has confirmed that the technology employed by DRIFT detectors has the capability to provide directional information of recoiling nuclei at the low energies of interest to dark matter searches. A Monte Carlo simulation has then been employed to determine the WIMP-nucleon sensitivity achievable using DRIFT detectors of the present performance, also examining what would be achievable if this was supplemented by a realistic active neutron veto detector. It is found that a CS2-filled DRIFT type detector running at a 500 NIP threshold ( 16 keV and 27 keV for C and S recoils respectively) for 300 kg years, and surrounded by the proposed veto scheme, would expect to observe a background of six un-vetoed events. The minimum positive signal above this background (90% C.L.) would correspond to a WIMP-nucleon sensitivity limit of 1.75×10−9 pb. This identifies the realistic limit of what can be achieved using gaseous CS2 as a target medium. An investigation into the limits achievable using a similar array in which DRIFT modules act as self-vetoing detectors is also examined providing insight into the future development and operation of the DRIFT programme.

A search for new examples of proton emission from ground and low lying states was conducted at Argonne National Laboratory. Of particular interest were examples of proton emission from nuclei which were deformed or had an odd number of neutrons, the majority of known proton emitters being odd-even and near-spherical. Candidate nuclei were created via fusion evaporation, these recoils then being separated according to their mass to charge ratio by the Fragment Mass Analyser, before being implanted into a Double Sided Silicon Strip Detector. Any subsequent alpha or proton decays were then recorded.

No description available.

<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.