[en] This thesis describes a set of experiments to investigate the properties of fully relaxed reactions in the mass 80 region. Symmetric and asymmetric entrance channels, leading to similar compound nuclei, have been compared in order to determine the characteristics of the reaction mechanism. The symmetric system ⁴⁰Ca + ⁴⁰Ca has been studied at laboratory energies of 197.3 and 230.5 MeV. The fissionlike products were detected by a series of six time of flight telescopes, placed at angles between 10^o and 52.4^o to the beam and a Bragg curve spectrometer-multiwire proportional chamber telescope, situated at 30^o. Data were collected in both singles and coincidence modes. To complement this measurement, fully damped yields from ²⁸Si + ^50,52,54Cr at 130 MeV and from ²⁸Si + ³⁰Cr at 150 MeV were measured using an array of four avalanche counter-silicon surface barrier detector telescopes spanning the angular range between 20^o and 50^o. The avalanche counters used in this experiment are of a new design. We present the features of this design and discuss the detectors' operational characteristics. Several possible interpretations of the data are considered. (author)

[en] A portal imaging system has been used, in conjunction with a movie measurement technique to measure set-up errors for 15 patients treated with radiotherapy of the pelvis and for 12 patients treated with radiotherapy of the brain. The pelvic patients were treated without fixation devices and the brain patients were treated with individually-moulded plastic shells. As would be expected the brain treatments were found to be more accurate than the pelvic treatments. Results are presented in terms of five error types: random error from treatment to treatment, error between mean treatment position and simulation position, random simulation error, systematic simulator-to-treatment errors and total treatment error. For the brain patients the simulation-to-treatment error predominates and random treatment errors were small (95% ≤ 3 mm, 77% ≤ 1.5 mm). Vector components of the systematic simulation-to-treatment errors were 1-2 mm with maximal random simulation error of ± 5 mm (2 S.D.). There is much interest in the number of verification films necessary to evaluate treatment accuracy. These results indicate that one check film performed at the first treatment is likely to be sufficient for set-up evaluation. For the pelvis the random treatment error is larger (95% ≤ 4.5 mm, 87% ≤ 3 mm). The systematic simulation-to-treatment error is up to 3 mm and the maximal random simulation error is ± 6 mm (2 S.D.). Thus corrections made solely on the basis of a first day check film may not be sufficient for adequate set-up evaluation

[en] The technique developed in this paper is particularly well suited to the detailed spectroscopic study of low energy quasi-elastic nuclear reactions and by overcoming the limitations of conventional procedure, the prospect of detailed studies of inclusive reaction mechanism may be realised. With only limited statistics we find evidence for strong multistep character in the transfer of a single nucleon from spherical vibrational target to spherical projectile nuclei. The suggestive measurements reported here may be made definitive through extended runs based on this technique and experiments planned for the future offer the real prospect of developing a quantified interpretation of the reaction process. 9 refs. 5 figs

[en] Quantitative calculations of sub-barrier fusion reactions are usually carrier out in the coupled channel formalism. There are, however, several questions that arise concerning this picture of the reactions. To address these questions, transfer channels in the sub-barrier region have been measured in the system nickel 58 + tin over a range of energies from the nominal Coulomb barrier to 40 MeV below this energy. Some difficulties with making these measurements are discussed. Data are presented for yields and cross sections

[en] A novel method of designing intensity modulated beams (IMBs) to achieve compensation in external beam radiotherapy of the breast, without the need for CT scans, is presented. The design method comprises three parts: (1) an electronic portal image is used to generate a map of radiological thickness; (2) this map is then used to obtain an estimate of the breast and lung outline; (3) a TMR-based dose calculation algorithm is then used to determine the optimum beam profile to achieve the best dose distribution. The dose distributions calculated for IMBs were compared with those calculated for the use of simple wedges. The results for two patients studied indicate that the dose inhomogeneity for IMBs is ±5%, compared with a value of ±10% for a wedged plan. The uncertainty in radiological thickness measurement corresponds to a dosimetric error of ±2%. Other errors associated with outline estimation are typically less than 2%, with a largest value of +5% for one of the patients who had a large and highly asymmetrical breast. The results for the two patients studied suggest that the uncertainties in the method are significantly smaller than the improvement in dose uniformity produced

[en] Measurements have been made of the θ/sub c.m./ = 180⁰ cross sections for transfer reactions of /sup 58/Ni+/sup 116,118,120,122,124/Sn at energies below the Coulomb barrier using a recoil mass separator. The largest single channel is for one-nucleon pickup, the cross section for which shows a strong dependence on target isotope. This dependence is correlated with the ground-state Q values for one-neutron pickup and is the same as that observed for subbarrier fusion for these systems

[en] The Rayleigh-Taylor instability has been investigated in accelerated planar foils. The foil in which the instability is to be observed is accelerated from one side using two laser beams, and backlit by thermonuclear alpha-particles from an adjacent implosion of a deuterium-tritium filled microballoon. The alpha-particles, after probing the unstable foil, are recorded in CR-39 plastic. Growth of the R-T instability leads to a thickness distribution across the foil, which can be directly determined from the energy of each particle recorded in CR-39, computed from high resolution measurements of the etched tracks. The technique is sensitive to small scale length instabilities ∼ 1 μm. Foils which are pre-perturbed, as well as planar foils driven by modulated laser beams, are used to seed the instability. The R-T instability has been observed in a number of foils. The range loss varies from almost zero to over 10 μm, and these variations in path length indicate the instability is present. (author)

[en] The results of experiments in which laser produced plasmas have been diagnosed by measurements of the charged thermonuclear reaction products are reported. Firstly, thermonuclear alpha particles from an exploding pusher target have been used to determine the growth of the Rayleigh-Taylor instability in a separate laser driven planar foil. The resulting alpha particle range loss distributions provide a direct measurement of the foil thickness distribution and hence the instability. The R-T instability has been observed in a number of foils with range losses varying between almost zero to over 10 μm. Secondly, a thermonuclear particle backlighting technique has been used in the measurement of the stopping power of hot plasma for different materials. The ratio of plasma stopping power to that of the cold material is measured and compared to a value obtained from theoretical modelling. The solid state nuclear track detector CR-39 has been used as a diagnostic for these experiments. A sophisticated image analysis system has been developed to enhance and improve data recovery. (author)

[en] An isodose distribution (collision kinetic energy distribution) was acquired using a megavoltage CT imaging system. Direct comparison of dose distributions has become important for verification in innovative treatment techniques. Three-dimensional implementation of this system is considered highly feasible. (author)

[en] Thermonuclear alpha-particles are produced in a 10psec burst from a laser compressed deuterium-tritium (DT) fusion target and are used to probe a foil simultaneously heated by laser beams to temperatures 50-500eV. The nuclear track detector CR-39 is used to record the tracks of alpha-particles which have passed through the foil. High resolution spectroscopy is employed to determine the residual energies in the CR-39 of the alpha-particles transmitted through the hot and adjacent cold material. These energies are compared, giving a direct measurement of the induced change in dE/dx. The experimental results are compared to theory by modelling the density and temperature distributions in the foil at the time of passage of the alpha-particles. Foils of CH₂, Al, Cu, and Au have been used to provide stopping power measurements of these materials to alpha-particles. (author)