A Moak type radio frequency ion source, capable of producing a pulsed beam of deuterons has been built for use with a Cockcroft-Walton accelerator. Pulsed deuterons striking a deuteron target produce neutrons in bursts thus allowing dynamic measurements of moderator and reactor core properties. Beam pulsing is accomplished by means of an einzel lens and an alternating potential applied to a pair of deflection plates. Proteins have been used exclusively in adjusting the source for optimum results since the radiation background due to the protons is much less than that due to deuterons. In actual experiments, however, when using deuterons, no modifications need to be made in the source. Beam currents have been measured at the source and at a target located at the end of the accelerator tube. Maximum currents measured are 150 microamperes and 60 microamperes respectively. Details of construction, maximum operating conditions, and oscillogram sof purse shapes are included in this report. / M.S.

Jets are a useful probe of the hot, dense medium produced in heavy ion collisions since partons are expected to lose energy in interactions with the medium through a phenomena called jet quenching. Recent results studying jet quenching in relativistic heavy ion collisions at the LHC with the ATLAS detector are presented here. The jets are reconstructed using the anti-kt algorithm with a background subtraction that removes the large underlying event. A fully unfolded measurement of the dijet asymmetry in Pb+Pb and pp collisions with an integrated luminosity of 0.14 nb^−1 and 4.0 pb^−1, respectively, at √sNN =2.76 TeV is shown. The dijets are found to be highly asymmetric in central Pb+Pb collisions and become more symmetric, or like pp, in more peripheral collisions. A strong p_T dependence to the asymmetry is also observed. This measurement is shown to have similar qualitative features at jet radii of R=0.3 and R=0.4, implying that the underlying event is under control. Measurements of the nuclear modification factor, R_AA, for R=0.4 jets in Pb+Pb and pp collisions with an integrated luminosity of 0.49 nb^−1 and 25 pb^−1, respectively, at √sNN = 5.02 TeV are also presented. The R_AA shows the strongest suppression in central collisions and the least suppression in peripheral collisions. It shows a slight increase with jet p_T and a decrease with increasing rapidity at high p_T. Finally, the dijet asymmetry for R=0.4 jets is also reported in Xe+Xe collisions at √sNN = 5.44 TeV compared to Pb+Pb and pp collisions at √sNN = 5.02 TeV. No difference is observed between Pb+Pb and Xe+Xe collisions, within the uncertainties of the measurement, as a function of the number of participants or the collision centrality.

Beams of polarized protons play an important part in the study of the spin dependence of the nuclear force by measuring the analyzing power in nuclear reactions. The source at iThemba LABS produces a beam of polarized protons that is pre-accelerated by an injector cyclotron (SPC2) to a energy of 8 MeV before acceleration by the main separated-sector cyclotron to 200 MeV for physics research. The polarized ion source is one of the two external ion sources of SPC2. Inside the ion source hydrogen molecules are dissociated into atoms in the dissociator and cooled to a temperature of approximately 30 K in the nozzle. The atoms are polarized by a pair of sextupole magnets and the nucleus is polarized by RF transitions between hyperfine levels in hydrogen atoms. The atoms are then ionized by electrons in the ionizer. The source has various sensitive devices, which influence beam intensity and polarization. Nitrogen gas is used to prevent recombination of atoms after dissociation. The amount of nitrogen and the temperature at which it is used plays a very important role in optimizing the beam current. The number of electrons released in the ionizer is influenced by the size and shape of the filament. Optimization of the source will ensure that beams of better quality (a better current and stability) are produced.

The 23Mg(pγ)24Al and 26Al(pγ)27Si astrophysical reactions are expected to be of considerable importance in the nucleosynthesis of A≥20 nuclei in classical novae. Previous studies have indicated that both reactions are dominated by resonant capture to excited states, above the proton-emission thresholds, in the proton-rich nuclei 24Al and 27Si, respectively. Consequently, by determining the nuclear properties of such resonant states it is possible to estimate the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates. In this thesis work, excited states in 24Al and 27Si were populated via the 10B(16O, 2n) and 12C(16O, n) heavy-ion fusion-evaporation reactions, respectively. The beams of 16O ions were produced by the Argonne Tandem Linear Accelerator System and prompt electromagnetic radiation was detected using the GAMMASPHERE detector array, which, in the case of the 24Al experiment, was used in coincidence with recoil selection provided by the Argonne Fragment Mass Analyzer. The two γray spectroscopy studies performed in this work allowed level structure determinations below the respective proton-emission thresholds of 24Al and 27Si nuclei, with improved precision on previous work. In addition to this, these studies also allowed a determination of the nuclear properties of proton-unbound astrophysically important γ decaying states, which, in turn, were used to re-evaluate the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates. The improved precision of the level energies and unambiguous assignments of resonant states has reduced the relative uncertainties in both the 23Mg(pγ)24Al and 26Al(pγ)27Si stellar reaction rates, constraining the production of A≥20 nuclei in classical novae.

No description available.

Student Number : 0000713F - PhD thesis - School of Physics - Faculty of Science / The Doppler shift and the Doppler broadening of prompt gamma emissions were measured for some residues formed in the interaction of 33 A MeV 12C ions with a 63Cu target using the AFRODITE detector array at Faure, Cape Town. This is a potentially new technique to carry out nuclear interaction studies. Coincident gamma rays emitted by the residues are used in their identification. Detection at angles other than 90◦ with respect to the beam axis gives the magnitude of the mean Doppler shifts and the average linear momentum transfer. The Doppler broadening of the detected gamma lines at 90 ◦ with respect to the beam axis could give the residue recoil angular distribution. The precise shapes of the Doppler shifted and broadened gamma lines for each of the residues extracted, reveals the distribution, in magnitude and angle, of the momentum transferred in the interaction process. In addition, characteristic gamma energy transitions of each residue populated carry additional information on angular momentum (spin) transfer, production cross-section and nuclear excitation states. The measured residues show a unique distribution of momentum ranging from single nucleon transfer to complete damping of the projectile momentum. The measured observables are consistent with the existing data from other techniques, making the new technique viable option for studying nuclear interaction kinematics. A comparison of the experimental measurements with the predictions of the model developed in Milano 1 and GEANT4 calculations shows that the model developed in Milano model give a much better agreement compared to the GEANT4 calculations, attributed to the assumption of projectile break-up and re-emission process of some of the fragments during the first step of the nuclear interaction process.

ATLAS measurements of the production of muons from heavy flavor decays in √sNN = 2.76 TeV Pb+Pb collisions and √s = 2.76 TeV pp collisions at the LHC are presented. Integrated luminosities of 0.14 nb−1 and 570 nb−1 are used for the Pb+Pb and pp measurements, respectively. The measurements are performed over the transverse momentum range 4 < pT < 14 GeV and for five Pb+Pb centrality intervals. Backgrounds arising from in-flight pion and kaon decays, hadronic showers, and mis-reconstructed muons are statistically re- moved using a template fitting procedure. The heavy flavor muon differential cross-sections and per-event yields are measured in pp and Pb+Pb collisions, respectively. The nuclear modification factor, RAA, obtained from these is observed to be independent of pT, within uncertainties, and to be less than unity, which indicates suppressed production of heavy flavor muons in Pb+Pb collisions. For the 0–10% most central Pb+Pb events, the measured RAA is ∼ 0.35. The azimuthal modulation of the heavy flavor muon yields is also measured and the associated Fourier coefficients vn for n=2, 3 and 4 are given as a function of pT and centrality. They vary slowly with pT and show a systematic variation with centrality that is characteristic of other anisotropy measurements. The measured RAA and vn values are also compared with theoretical calculations. We also present the ATLAS di-muon azimuthal correlation from heavy flavor decay in √√sNN = 5.02 TeV Pb+Pb collisions and s = 5.02 TeV pp collisions. Heavy flavor muons with 4 < pT < 8 GeV are selected. The azimuthal correlations are measured for both same sign muon pairs and opposite sign muon pairs. Comparing with the azimuthal correlations in pp data, Pb+Pb results are observed to have more broadening. Central collisions are also more broadened than peripheral collisions. The integrated luminosities used in the dimuon measurement are 26 pb−1 for the pp data and 0.49 nb−1 for the Pb+Pb data. In ultra-relativistic heavy-ion collisions, dilepton pairs may be produced through the interaction of the large electromagnetic fields of the nuclei. A measurement of γγ → μ+μ− in inclusive Pb+Pb collisions at √sNN = 5.02 TeV using 0.49 nb−1 is presented in this thesis. The contribution from background sources of dimuons is removed using a template fit method. The angular and transverse momentum correlations between the muons are measured as a function of collision centrality. In peripheral collisions, the muons exhibit a strong back-to-back correlation consistent with previous measurements of dimuon production in ultra-peripheral collisions. The correlations are observed to broaden significantly in central collisions. The modifications are qualitatively consistent with attenuation of the muons while passing through the hot matter produced in the collision.

No description available.

Charged particle beams are an increasingly common method of cancer treatment. Because of their Bragg peak dose distribution, protons are an effective way to deliver a dose to the tumor, while minimizing the dose to surrounding tissue. Charged particles with greater mass and higher charge than protons have an even sharper Bragg peak and a higher Relative Biological Effectiveness (RBE), allowing a greater dose to be delivered to the tumor and sparing healthy tissue. Since carbon ions are being implemented for treatment in Europe and Japan, this study will focus on carbon as the heavier ion of choice. Comparisons are drawn between moderated and unmoderated protons and carbon ions, all of which have a penetration depth of 10 cm in tissue. Scattering off the beam line, dose delivered in front of and behind the tumor, and overall dose mapping are examined, along with fragmentation of the carbon ions. It was found that fragmentation of the carbon ion beam introduced serious problems in terms of controlling the dose distribution. The dose to areas behind the tumor was significantly higher for carbon ions versus proton beams. For both protons and carbon ions, the use of a moderator increased the scattering off of the beam line, and slightly increased the dose behind the tumor. For carbon ions, the use of a moderator increased the degree of fragmentation throughout the beam path.

In conventional radiotherapy for tumor treatment, photons are used to impart an energetic dose inside a tumor with the goal of killing the cancerous cells. This process is intrinsically inefficient due to the fact that photons lose their energy exponentially with depth causing the highest dose to occur in overlying healthy tissue. However, charged particles with a mass of 1 amu or greater lose their energy in a manner that allows for a high dose to be localized at significant depth. The area of high dose localization is known as the Bragg Peak. Exploitation of the Bragg Peak could lead to more efficient non-invasive treatment plans by reducing the dose in healthy tissues. Using the Particle and Heavy Ion Transport System (PHITS), the dose and fragmentation particles from ions of 1H, 4He, 7Li, 12C, 16O, and 20Ne were found at varying depths in a water phantom. A water filled cylindrical phantom with a radius of 10 cm was used to mimic a human body. The energy of each ion was selected so that the Bragg Peak would occur approximately 10 cm into the depth of the water phantom where a 1 cm radius water sphere was placed to simulate a solid tumor. Dose equivalent localization rates within the tumor were found to be 14.5, 36.5, 45.7, 49.5, 41.3, and 34.1 percent for 1H, 4He, 7Li, 12C, 16O, and 20Ne, respectively. The percentage of dose within the tumor increased with increasing atomic number up to 12C, decreasing thereafter. The total dose distal from the tumor ranged from 0.1, 0.9, 2.8, 0.9, 0.5, and 0.6 percent for the ions ordered by their masses. Complementing its high dose in the tumor, carbon was seen to experience the lowest amount of dose escaping due to fragmentation and scattering, on a dose normalized basis.