Investigation of the 2+ Hoyle state candidates in 12C

Thesis (PhD)--Stellenbosch University, 2015.ENGLISH ABSTRACT: Over the years the 12C nucleus has proved to be one of the most fascinating nuclei to study. This thesis attempts to provide answers regarding some of the open questions regarding certain structural properties of this nucleus. This is done by performing two independent experiments to measure the 12C excitation energy spectrum. The frst experiment was aimed at investigating the existence of the 11.16 MeV 2+ state claimed to exist in 12C. The measurement was performed with the K600 magnetic spectrometer at iThemba LABS, South Africa, using the 11B(3He,d) 12C reaction with a 44 MeV 3He beam at three different laboratory angles θlab = (25° , 30° , 35° ). The results obtained showed no evidence of such a state in 12C and it was concluded that no such state exist. The results also showed signatures of a 2+ state in the 10 MeV excitation energy region. This state is associated with the 2+ excitation of the well known Hoyle state reported to exist at this region. A second experiment was aimed at searching for the 2+ excitation of the Hoyle state in the 10 MeV excitation energy region. This was achieved by using the 14C(p,t) 12C[3α] reaction with a 66 MeV proton beam and observing tritons at a laboratory angle of θlab = 21° . The measurement was performed with the K600 magnetic spectrometer in conjunction with silicon detectors mounted inside the scattering chamber. The peak fitting analysis performed on a singles event spectrum showed evidence of the population of the 2+ state at Ex = 9.69 ± 0.11 MeV and width of Γ = 1.43 ± 0.22 MeV. These parameters appear to shift when the coincidence events are taken into account. The parameters obtained for decay to the 8Be ground state decay mode are Ex = 9.97 ± 0.20 MeV and Γ = 1.03 ± 0.21 MeV for energy and width respectively. Whereas, the parameters obtained by gating on other decay modes are Ex = 9.55 ± 0.22 MeV and Γ = 1.15 ± 0.24 MeV for energy and width respectively. The newly found state decays predominately via the 8Be ground state decay mode.AFRIKAANSE OPSOMMING: Oor die jare heen was die 12C kern nog altyd bekend as 'n fasinerende kern vol geheimenisse. In hierdie tesis word gepoog om antwoorde te verskaf vir ope vraagstukke ten opsigte van die struktuur van hierdie kern. Ten einde hierdie doelwit te bereik is twee onafhanklike eksperimente aangepak opgewekte toestand van 12C te ondersoek. In die eerste eksperiment word die algemeen aanvaarde aanname ondersoek dat 'n 2+ toestand by 'n opwekkings energie van 11.16 MeV in 12C bestaan. Die ekspe-rimentele werk is gedoen met behulp van die K600 magnetiese spektrometer by iThemba LABS (Suid Afrika). Die 11B(4He,d) 12C reaksie is gebruik vir die ondersoek by drie verskillende verstrooiingshoeke (θlab = 25◦ ,30◦ ,35◦ ) met 'n 44 MeV 3He bundel. Uit die resultate is dit duidelik dat geen 2+ toestand waargeneem is in die omgewing van 11.16 MeV nie. Die resultate dui egter op die moontlikheid dat 'n 2+ toestand bestaan rondom die opwekking energie van 10 MeV. Hierdie toestand, ook waargeneem in ander onlangse eksperimente, word geassosieer met die 2+ opgewekte toestand van die beroemde Hoyle toestand. Die doel van die tweede eksperiment was om hierdie 2+ opgewekte toestand te karakteriseer. 'n Proton bundel met kinetiese energie van 66 MeV is gebruik om die 14C(p,t) 12C[3α] reaksie te ondersoek by 'n triton verstrooiingshoek van 21◦ . Die eksperimentele werk is uitgevoer met behulp van die K600 magnetiese spektrometer tesame met 'n aantal silikon detektors. 'n Piekpassing analise van die opwekking energie spektrum dui op die teenwoordigheid van 'n 2+ toestand by Ex = 9.69 ± 0.11 MeV met 'n wydte van Γ=1.43 ± 0.22 MeV. Hierdie parameters blyk te verander wanneer die verval van die toestand deur α-verval in ag geneem word. Die opwekking energie spektrum wat gemeet word in koinsidens met α-verval sodanig dat die oorblywende 8Be kern in die grondtoestand bly dui op 'n 2+ toestand by Ex = 9.97 ± 0.20 MeV met 'n wydte van Γ = 1.03 ± 0.21 MeV. Indien die som totaal van al die ander verval modes beskou word verander die posisie en wydte van die toestand na Ex = 9.55 ± 0.22 MeV en Γ = 1.15 ± 0.24 MeV. Dit is bepaal dat die 2+ toestand hoofsaaklik verval via α-verval wat die oorblywende 8Be kern in die grondtoestand laat

Investigation into the gas mixing effect in ECRIS plasma using Kα and optical diagnostics

Mixing a lighter gas species into the plasma of an ECRIS is known to enhance high charge state production of the heavier gas species. With this investigation, Kα diagnostics, optical emission spectroscopy and the measured charge state distribution of the extracted beam were combined to shed more light on the physics governing this phenomenon. Kα diagnostics data from two ion sources, the JYFL 14 GHz ECRIS and the GTS at iThemba LABS, are presented to gain confidence on the observed trends. The results seem to favor ion cooling as the most likely mechanism responsible for the favorable influence of the gas mixing.peerReviewe

Encapsulated Sulfur targets for light ion beam experiments

A new method was developed to produce enriched Sulfur targets with minimum loss of material. This was made possible by inserting Sulfur in-between two 0.5 μm Mylar foils (C10H8O4). The initial aim was to ensure that the Sulfur targets reduce by no more than 50% of the initial thickness within 24 hours under the equivalent of 10 J/cm2 of integrated energy deposition by an energetic (Eb > 50 MeV) proton beam. There is no loss of enriched material while making the target, as all the material is deposited within the surface area to be exposed to the beam. During beam irradiation, the targets were frequently swivelled in order to expose each part of the target to the beam and achieve homogeneous irradiation. Targets of 0.4 mg/cm2 thickness were produced and characterised using ion beam analysis technique with a 3 MeV proton beam

Encapsulated Sulfur targets for light ion beam experiments

International audienceA new method was developed to produce enriched Sulfur targets with minimum loss of material. This was made possible by inserting Sulfur in-between two 0.5 μm Mylar foils (C10H8O4). The initial aim was to ensure that the Sulfur targets reduce by no more than 50% of the initial thickness within 24 hours under the equivalent of 10 J/cm2 of integrated energy deposition by an energetic (Eb > 50 MeV) proton beam. There is no loss of enriched material while making the target, as all the material is deposited within the surface area to be exposed to the beam. During beam irradiation, the targets were frequently swivelled in order to expose each part of the target to the beam and achieve homogeneous irradiation. Targets of 0.4 mg/cm2 thickness were produced and characterised using ion beam analysis technique with a 3 MeV proton beam

Encapsulated Sulfur targets for light ion beam experiments

A new method was developed to produce enriched Sulfur targets with minimum loss of material. This was made possible by inserting Sulfur in-between two 0.5 μm Mylar foils (C10H8O4). The initial aim was to ensure that the Sulfur targets reduce by no more than 50% of the initial thickness within 24 hours under the equivalent of 10 J/cm2 of integrated energy deposition by an energetic (Eb > 50 MeV) proton beam. There is no loss of enriched material while making the target, as all the material is deposited within the surface area to be exposed to the beam. During beam irradiation, the targets were frequently swivelled in order to expose each part of the target to the beam and achieve homogeneous irradiation. Targets of 0.4 mg/cm2 thickness were produced and characterised using ion beam analysis technique with a 3 MeV proton beam

Development of New Target Stations for the South African Isotope Facility

The development of new target stations for radioisotope production based on a dedicated 70 MeV commercial cyclotron (for protons) is described. Currently known as the South African Isotope Facility (SAIF), this initiative will free the existing separated-sector cyclotron (SSC) at iThemba LABS (near Cape Town) to mainly pursue research activities in nuclear physics and radiobiology. It is foreseen that the completed SAIF facility will realize a three-fold increase in radioisotope production capacity compared to the current programme based on the SSC