.
A survey of the fine structure of the Isovector Giant Dipole Resonance (IVGDR) was performed, using the recently commissioned Zero-degree Facility of the K600 magnetic spectrometer at iThemba LABS. ...Inelastic proton scattering at an incident energy of 200MeV was measured on
27
Al ,
40
Ca ,
56
Fe ,
58
Ni and
208
Pb . A high energy-resolution (
Δ
E
≃
40
keV FWHM) could be achieved after utilising faint-beam and dispersion-matching techniques. A considerable fine structure is observed in the energy region of the IVGDR and characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The comparison with Quasiparticle-Phonon Model (QPM) calculations provides insight into the relevance of different giant resonance decay mechanisms. Photoabsorption cross sections derived from the data assuming a dominance of relativistic Coulomb excitation are in fair agreement with previous work using real photons.
The phenomenon of fine structure of the Isoscalar Giant Quadrupole Resonance (ISGQR) has been studied with high energy-resolution proton inelastic scattering at iThemba LABS in the chain of stable ...even-mass Nd isotopes covering the transition from spherical to deformed ground states. A wavelet analysis of the background-subtracted spectra in the deformed 146, 148, 150Nd isotopes reveals characteristic scales in correspondence with scales obtained from a Skyrme RPA calculation using the SVmas10 parameterization. A semblance analysis shows that these scales arise from the energy shift between the main fragments of the K=0,1 and K=2 components.
Carbon-modified titanium dioxide nanoparticles (C:TiO2 NPs) have been synthesized by ultrasonic nebulizer spray pyrolysis (USP) and pneumatic spray pyrolysis (PSP) techniques. HRTEM on the NPs shows ...difference in lattice spacing in the NP structures prepared by the two methods—2.02 Å for the USP NPs and an average of 3.74 Å for the PSP NPs. The most probable particle sizes are 3.11 nm and 5.5 nm, respectively. Raman spectroscopy supported by FTIR confirms the TiO2 polymorph to be anatase with the intense phonon frequency at 153 cm−1 blue-shifted from 141 cm−1 ascribed to both carbon doping and particle size. A modified phonon confinement model for nanoparticles has been used to extract phonon dispersion and other parameters for anatase for the first time. Electronic measurements show “negative conductance” at some critical bias voltage, which is characteristic of n-type conductivity in the carbon-doped TiO2 NPs as confirmed by the calculated areas under the I-V curves, a property suited for solar cell applications. Practical solar cells built from carbon-doped TiO2 electrodes show up to 1.5 times improvement in efficiency compared to pure TiO2 electrodes of similar construction.
Experiments investigating the fine structure of the IsoScalar Giant Monopole Resonance (ISGMR) of 48Ca were carried out with a 200 MeV alpha inelastic-scattering reaction, using the high ...energy-resolution capability and the zero-degree setup at the K600 magnetic spectrometer of iThemba LABS, Cape Town, South Africa. Considerable fine structure is observed in the energy region of the ISGMR. Characteristic energy scales are extracted from the experimental data by means of a wavelet analysis and compared with the state-of-the-art theoretical calculations within a Skyrme-RPA (random phase approximation) approach using the finite-rank separable approximation with the inclusion of phonon-phonon coupling (PPC). Good agreement was observed between the experimental data and the theoretical predictions.
The radiation damage in polyvinyl toluene based plastic scintillator EJ200 obtained from ELJEN technology was investigated. This forms part of a comparative study conducted to aid in the upgrade of ...the Tile Calorimeter of the ATLAS detector during which the Gap scintillators will be replaced. Samples subjected to 6 MeV proton irradiation using the tandem accelerator of iThemba LABS, were irradiated with doses of approximately 0.8 MGy, 8 MGy, 25 MGy and 80 MGy. The optical properties were investigated using transmission spectroscopy whilst structural damage was assessed using Raman spectroscopy. Findings indicate that for the dose of 0.8 MGy, no structural damage occurs but a breakdown in the light transfer between base and fluor dopants is observed. For doses of 8 MGy to 80 MGy, structural damage leads to hydrogen loss in the benzene ring of the PVT base which forms free radicals. This results in an additional absorptive component causing increased transmission loss as dose is increased.
In this study we look at radiation damage and its adverse effects on plastic scintillators housed within the Tile Calorimeter (TileCal) of the ATLAS detector. The study focuses on determining how the ...interaction of ionizing radiation with plastic scintillators effects their efficacy and desired properties such as high light output and fast decay time. Plastic scintillators form an integral part of the ATLAS trigger system and their optimal functionality is paramount to the success of ATLAS. Electron paramagnetic resonance (EPR) provides insight into the electronic structure of the plastics and can characterize the damage caused by ionizing radiation. Density functional theory (DFT) calculations will be performed in order to simulate the EPR signal. Preliminary EPR results investigate four different types of plastic scintillators. These include three polyvinyl-toluene based Eljen technologies: EJ200, EJ208 and EJ260, and one polystyrene based Dubna sample. It has been observed that the Dubna sample, identical on the current scintillator used in the ATLAS detector, undergoes more structural damage when compared to the Eljen samples.
Fine structure in the energy region of the isoscalar giant quadrupole resonance in nuclei is observed in high-resolution proton scattering experiments at iThemba LABS over a wide mass range. A novel ...method based on wavelet transforms is introduced for the extraction of scales characterizing the fine structure. A comparison with microscopic model calculations including two-particle two-hole (2p2h) degrees of freedom identifies the coupling to surface vibrations as the main source of the observed scales. A generic pattern is also found for the stochastic coupling to the background of the more complex states.
We report on the radiation damage to the optical properties of plastic scintillators following irradiation using a 6MeV proton beam produced by the 6MV tandem accelerator of iThemba LABS, Gauteng. A ...comparative is drawn between polyvinyl toluene based commercial scintillators EJ200, EJ208, EJ260 and BC408 as well as polystyrene based scintillator UPS923A and scintillators manufactured for the Tile Calorimeter. Results on the proton induced damage indicate a reduction in the light output and transmission capability of the plastics. Scintillators containing a larger Stokes shift, i.e. EJ260 and EJ208 exhibit the most radiation hardness. The EJ208 is recommended as a candidate to be considered for the replacement of Gap scintillators in the Tile Calorimeter for the 2018 upgrade.
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