Browsing by Author "Mdhluli, Joyful Elma"

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    Magnetic properties in diamond induced by proton irradiation
    (2017) Mdhluli, Joyful Elma
    Ultra-pure type II-a diamond was irradiated with 2,2 MeV of protons with a fluence of 5:0 1017ions=cm2 at Universidad Autonoma de Madrid (UAM) using the 5 MV Tandem accelerator at the Centre for Microanalysis of Ma- terials (CMAM). Magnetic measurements before and after irradiation were performed using the MPMS XL (5T) system that consists of the Super- conducting Quantum Interference Device (SQUID) at the Consejo Superior de Investigaciones Cient cas (CSIC). The sample was further characterised using low temperature magnetic fi eld microscopy (MFM) and Raman Spec- troscopy. The magnetization curves of the pristine (un-irradiated) sample exhibited an almost perfect diamagnetic signal which was independent of temperature. The diamagnetic signal obtained was 4:75 107 emu=g and was in agreement with that found in literature [1]. A very weak magnetic contribution was observed at 4.2 K though not at room temperature in the pre-irradiation measurements. The magnetization curves at 300 K and 4.2 K after ir- radiation and the thermal cycle at 2 kOe exhibited a similar diamagnetic behaviour to that of the pristine sample with a small and positive magnetic contribution appearing above the previous diamagnetic background. The main outcome of the irradiation seemed to be a paramagnetic contribution but there were additional superparamagnetic and ferromagnetic-like contri- butions which were also observed. Raman spectra indicate graphitization on the irradiated area. An appar- ent blueshit was observed in the main diamond peak that was relative to 1332 cm-1. The irradiated region that was not graphitized showed a little disorder within the structure of diamond as expected on an area that was heavily irradiated by protons. The damage was tens of microns into the sample. The graphitized region showed the G-peak at around 1600 cm-1 of the damaged diamond that is beyond the graphitization limit. The irradi- ated region showed a mixture of the sp3 and sp2 orbitals that are related to the peak at 1330 cm-1 of diamond and the 1580 cm-1 peak related to the G- band of graphite. The sp2 orbitals corresponded to the micro-polycrystalline graphite that is often seen in irradiated diamond. It has been previously ob- served that the defects have a tendency of clustering into graphitic islands and swell after high dose implantations. Magnetic measurements show a decrease in the diamagnetic signal of the sample showing that the irradiation has a ected the magnetic signal of the sample. A magnetic signal was observed in the MFM image with a negative contrast, this was observed by the darker regions relative to the pure dia- mond corresponding to the graphitic/graphitized region in the topography image. The negative contrast was not completely clear in the MFM image but it can be observed that there is a change in contrast between the irra- diated and un-irradiated region. From the SQUID analyses, Raman measurements and MFM analysis, we can safely conclude that the irradiation resulted in the mixture of sp2 and sp3 orbitals that graphitized the irradiated surface. As it was concluded from the Raman analyses, any magnetic signal measured over the graphi- tized irradiated region is attributed to the ion induced modi cation of the diamond structure.
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    Probing heavy-quark production vs charged-particle multiplicity in pp collisions at √ s = 5.02 TeV with ALICE
    (2024) Mdhluli, Joyful Elma
    The differential heavy-flavour (charm and beauty quark) production as a function of the charged-particle multiplicity is investigated in pp collisions at √ s = 5.02 TeV. The heavy-quark production cross section as a function of transverse momentum (pT) and pseudorapidity (η) is also evaluated. The measurement of the inclusive yield of heavy quarks via the single-muon (µ) decay channel is done in the muon spectrometer at forward pseudorapidity (−4 < η < −2.5) and the charged-particle multiplicity using the Silicon Pixel Detector at central pseudorapidity (|η| < 1). These measurements are important in order to gain more insight into which processes are involved in the collision at a partonic level as well as provide information on the interplay between hard and soft mechanisms during particle production. Reference data taken during Run 2 in 2015 and 2017 in pp collisions at √ s = 5.02 TeV are analyzed for measurements of the inclusive heavy-flavour decay muon differential cross-section and heavy-flavour decay muon yield as a function of the charged-particle multiplicity. A total number of 102.7 M (21.34 M) events for the single muon low (high)- pT triggers are analyzed for both measurements. Minimum bias triggered events with multiplicity tracklets > 0 are used for multiplicity estimation. Two methodologies are utilized, the data-driven method and the ”Official Framework”. Results of inclusive heavy-flavour decay muon differential cross-section measured as a function of pT are compared with the theoretical model FONLL, the data and theoretical model are in agreement within systematic uncertainties. The results are also compared with measurements in pp collisions at √ s = 7 TeV, an energy dependence is observed. Results of inclusive heavy-flavour decay muon yield as a function of the charged-particle multiplicity indicated an approximately faster than linear correlation. Comparisons with other heavy-quark measurements vs charged-particle multiplicity is made and the measurements are in agreement at low charged-particle multiplicities. This thesis also reports on the Service Task work done. This entailed tests performed on detector elements of the Muon Chambers (MCH) that suffered high-voltage trips that were repaired during the long shutdown (LS2). The detector elements were successfully repaired and are currently stored as spares for the Run 3 data-taking period.