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Spectroscopy of 50Ti through internal-pair formation
Thesis (PhD)--Stellenbosch University, 2023.
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2023
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| _version_ | 1867613791145951232 |
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| access_status_str | Open Access |
| author | Chisapi, Maluba Vernon |
| author2 | Jones, P. |
| author_browse | Chisapi, Maluba Vernon Jones, P. |
| author_facet | Jones, P. Chisapi, Maluba Vernon |
| author_sort | Chisapi, Maluba Vernon |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2023. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/128692 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:41:45.229Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/128692 Spectroscopy of 50Ti through internal-pair formation Chisapi, Maluba Vernon Jones, P. Newman, R. T. Stellenbosch University. Faculty of Science. Dept. of Physics. Electric monopoles Magnetic monopoles -- Mathematical models Magnetic lenses Nuclear shapes Electron-positron pairs Electron spectroscopy Atomic nuclei Spectrometer -- Calibration UCTD Thesis (PhD)--Stellenbosch University, 2023. ENGLISH ABSTRACT: Electric monopole (E0) transitions are closely tied to shape coexistence in atomic nuclei. Th E0 transition strength, ρ²(E0), is directly connected to nuclear mean-square charge radii. A large E0 transition strength is a reliable indicator of nuclear shape coexistence and strong mixing between admixture states of different deformation. Electric monopole transitions are possible between states of the same spin and parity such as two 0⁺ states. They proceed via internal conversion and internal-pair formation. Detecting conversion electrons and electron-positron pairs is normally done using magnetic lens spectrometers. A solenoid magnetic lens spectrometer was successfully refurbished and upgraded, giving it the capability to measure internal-pair formations (IPF) in addition to internal conversion electrons (ICE), at the iThemba Laboratory for Accelerator Based Sciences, in Cape Town, South Africa. The equipment can be coupled to other facilities or integrated into the existing beamlines. The smaller detector mount point in the original design of the electron spectrometer which only accommodated 300-500 mm2 active area, 2-5 mm thick single crystal Si(Li) detectors was replaced by a mount point with provision for a much larger 2800 mm2 active area, 11 mm thick segmented LEPS detector. The LEPS detector was adapted by replacing the thicker, 300 µm beryllium, window on the end-cap with a thinner, 0.5 µm Mylar window in order to minimise particle energy loss. Efficiency of the refurbished spectrometry system was optimised with the aid of Geant4 simulations and was estimated between 45% and 50% for 1 MeV electrons or positrons at 500 G magnetic field. The lens spectrometer was coupled with a mini γ-array comprised of seven Compton-suppressed HPGe Clover detectors, which gave additional experimental capabilities such as measuring γ-rays in coincidence with internal conversion electrons (ICE), and internal-pairs (IPF). Testing for proof of principle was done through measurements with the 207Bi radioactive source, and the experimental ICC values of 570 keV and 1064 keV K, L, M -shell electrons were determined and compared to literature. An in-beam experiment involving a 30 MeV α-beam on a 96% enriched 50Ti self-supporting target was performed to investigate the 3868.3 keV E0 (0⁺ → 0⁺) electric monopole transition and its alternative E2 (0⁺ → 2⁺) transition. The in-beam experimental campaign was not only a commissioning experiment for the newly refurbished magnetic lens spectrometer, but it was also part of the larger endeavour to characterise excited 0⁺ states and E0 transitions in the N Z 28 region of the nuclear chart. The state of interest was expected to be populated by the 50Ti(α, αI )50Ti inelastic scattering reaction but judging by the significant yield of the 50,51,52Cr, 50,49,48,47Ti and 52,51V residual nuclei, it was clear that the experiment proceeded via fusion-evaporation reaction instead. Gamma-ray transitions of these residual nuclei were thoroughly investigated and level schemes have been built. In addition, over ten conversion electrons were identified in the singles mode. AFRIKAANSE OPSOMMING: Elektriese monopool (E0) oorgange is nou verbind om naasbestaan in atoomkern vorme. Die E0-oorgangssterkte, ρ²(E0), is direk verbind aan kern gemiddelde-vierkante lading radiusse. ’n Groot E0-oorgangssterkte is a betroubare aanwyser van kernvorm naasbestaan en sterk vermenging tussen vermengingstoestande van verskillende vervorming. Elektriese monopool oorgange is moontlik tussen toestande van dieselfde spin en pariteit soos twee 0⁺ toestande. Hulle verval deur interne omskakeling en interne-paarvorming. Die opsporing van omskakelingselektrone en elektron-positronpare word normaalweg gedoen met behulp van magnetiese lensspektrometers. ’n Solenoïde magnetiese lensspektrometer is suksesvol opgeknap en opgegradeer, wat dit die vermoë gee om interne-paarformasies (IPF) bykomend tot interne omskakelingselektrone (ICE) te meet, by die iThemba Laboratorium vir Versnellergebaseerde Wetenskappe, in Kaapstad, Suid Afrika. Die toerusting kan gekoppel word aan ander fasiliteite of geïntegreer word in die bestaande bundellyne. Die kleiner detektor monteerpunt in die oorspronklike ontwerp van die elektronspektrometer wat slegs ’n 300-500 mm2 aktiewe area, 2-5 mm dik enkelkristal Si(Li) detektor akkommodeer, is vervang deur ’n monteerpunt met voorsiening vir ’n baie groter 2800 mm2 aktiewe area, 11 mm dik gesegmenteerde LEPS-detektor. Die LEPS-detektor is aangepas deur die dikker, 300 µm berillium, venster op die einddop te vervang met ’n dunner, 0.5 µm Mylar-venster om deeltjie-energieverlies te minimaliseer. Die doeltreffendheid van die opgeknapte spektrometriestelsel is met behulp van Geant4 simulasies geoptimaliseer en is geskat tussen 45% en 50% vir 1 MeV elektrone of positrone by 500 G magnetiese veld. Die lensspektrometer is gekoppel aan ’n mini γ-skikking wat bestaan uit sewe Compton-onderdrukte HPGe Clover-detektors, wat bykomende eksperimentele vermoëns gee soos die meet van γ-strale in ooreenstemming met interne omskakelingselektrone (ICE) en interne pare (IPF). Toets vir bewys van beginsel is gedoen deur metings met die 207Bi radioaktiewe bron, en die eksperimentele ICC waardes van 570 keV en 1064 keV K, L, M-skil elektrone is bepaal en met literatuur waardes vergelyk. ’n “In-beam” eksperiment wat ’n 30 MeV α-bundel op ’n 96% verrykte 50Ti selfondersteunende teiken behels, was uitgevoer om die E0 3868.3 keV (0⁺ → 0⁺) elektriese monopool oorgang en sy alternatiewe E2 (0⁺ → 2⁺) oorgang te ondersoek. Die eksperimentele veldtog met bundel was nie net ’n ingebruikneming eksperiment vir die nuut opgeknapte magnetiese lens spektrometer, maar dit was ook deel van die groter poging om opgewonde 0⁺ toestande en E0 oorgange in die N Z 28 gebied van die kernkaart te karakteriseer. Die toestand van belang was na verwagting opgewek deur die 50Ti(α, αl )50Ti onelastiese verstrooiingsreaksie maar te oordeel aan die beduidende opbrengs van die 50,51,52Cr, 50,49,48,47Ti en 52,51V oorblywende kerne, was dit duidelik dat die eksperiment eerder deur samesmelting-verdampingsreaksies gekenmerk word. Gammastraaloorgange van hierdie oorblywende kerne is deeglik ondersoek en vlakskemas is gebou. Daarbenewens is meer as tien omskakelingselektrone in die enkelspelmodus entifiseer. Doctoral 2023-02-17T07:12:54Z 2023-11-16T08:30:26Z 2023-02-17T07:12:54Z 2023-11-16T08:30:26Z 2023-04 Thesis https://scholar.sun.ac.za/handle/10019.1/128692 en_ZA Stellenbosch University xvii, 126 pages : illustrations (some color) application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Electric monopoles Magnetic monopoles -- Mathematical models Magnetic lenses Nuclear shapes Electron-positron pairs Electron spectroscopy Atomic nuclei Spectrometer -- Calibration UCTD Chisapi, Maluba Vernon Spectroscopy of 50Ti through internal-pair formation |
| title | Spectroscopy of 50Ti through internal-pair formation |
| title_full | Spectroscopy of 50Ti through internal-pair formation |
| title_fullStr | Spectroscopy of 50Ti through internal-pair formation |
| title_full_unstemmed | Spectroscopy of 50Ti through internal-pair formation |
| title_short | Spectroscopy of 50Ti through internal-pair formation |
| title_sort | spectroscopy of 50ti through internal pair formation |
| topic | Electric monopoles Magnetic monopoles -- Mathematical models Magnetic lenses Nuclear shapes Electron-positron pairs Electron spectroscopy Atomic nuclei Spectrometer -- Calibration UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/128692 |
| work_keys_str_mv | AT chisapimalubavernon spectroscopyof50tithroughinternalpairformation |