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postgraduate thesis: Shape co-existence of neutron-rich 69, 71, 73Co nuclei

TitleShape co-existence of neutron-rich 69, 71, 73Co nuclei
Authors
Advisors
Advisor(s):Lee, HCJXie, MH
Issue Date2019
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Lokotko, T.. (2019). Shape co-existence of neutron-rich 69, 71, 73Co nuclei. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.
AbstractShell model works well in the valley of stability as it successfully explains the existence of magic numbers (2, 8, 20, 28, 50 ...). It was expected the shell model would work in regions far from stability. De- velopment of new facilities that work with radioactive beams opened a way to study nuclear physics far from stability. During recent exper- iments with unstable isotopes, interesting phenomena were revealed - new magic numbers started to evolve in the shell structure. For exam- ple, in proton closed shell of Ni nucleus (Z = 28) new magic number N = 40 was found. Theoretical development of many-body quantum systems revealed in- teresting phenomena in subatomic physics. On the one hand, stabilis- ing effects in closed shells and sub-shells lead nucleus to self-organise into spherical shapes. On the other hand, residual interactions, such as pairing forces between protons and neutrons, were forcing nucleus into deformed shape. Interplay between two opposite effects in someparticular nuclei exhibited energy eigenstates corresponding to differ- ent shapes. This phenomena is called shape coexistence, or shape isomerism. Discovering and interpreting these phenomena in nuclei close to the drip line is one of the most important topics in theoretical and experimental nuclear physics. Recently, the region around doubly magic radioactive isotope has drawn significant attention, as 68 68 Ni Ni was found to share spheri- cal features in ground state, while signatures of shape coexistence in the excited band were found. These experimental results motivate to study the region around magic numbers Z = 28, N = 40 for the evolu- tion of shape coexistence features. Moving along the N = 40 isotone line, only 2 protons less, the 66 Fe isotope was found quit deformed in ground state with no evidence of shape coexistence. Co isotopes are good candidates for studying shape isomerism in this region. 67 deformed Co was found to share features of both spherical 66 Fe. Shape coexistence of 67 a prolate proton-intruder state coupled to the of shape isomerism in Ni and Co is explained by the super- position of a proton f 7/2 hole state coupled to the spherical 67 68 66 68 Ni and Fe isotope. Existence Co pointed attention to shape evolution in heavier Co nuclei, namely 69,71,73 Co, and to shell transformation from N = 40 to N = 50. Shape coexistence of Co nuclei was studied during an in-beam gamma experiment at the Radioactive Isotope Beam Factory, RIKEN Nishina centre, Japan. 69,71,73 Co isotopes were produced via the knockout re- actions, when a secondary beam of 70,72,74 Ni and 72 Co nuclei at energy of 260 MeV/μ bombarded a liquid hydrogen target of MINOS device. The MINOS target was made with a length of 100mm to increase the total amount of nuclear reactions. The MINOS target chamber was surrounded by the time projection chamber which was used to reconstruct vertex of the reactions, improving energy resolution dur- ing the Doppler corrections. Energies of the γ-rays were measuredby the DALI2 NaI(Tl) detector array. Level scheme of low-lying ex- cited states was reconstructed using γ-γ coincidence technique. Lenzi- Nowacki-Poves-Sieja (LNPS) model of nuclear interaction was chosen for comparison with the experimental data. Strong signatures of shape coexistence were found in spectrums of 69,71 Co isotopes, as two struc- ture coexist - spherical and deformed bands. Due to the insufficient statistics only spherical structure were clearly seen in spectrum of 73 Co nucleus. In this thesis the evolution of shell structure in 69,71,73 Co isotopes will be discussed together with the physics behind shape co- existence in neutron-rich Co nuclei.
DegreeDoctor of Philosophy
SubjectCobalt - Isotopes
Nuclear physics
Dept/ProgramPhysics
Persistent Identifierhttp://hdl.handle.net/10722/281303

 

DC FieldValueLanguage
dc.contributor.advisorLee, HCJ-
dc.contributor.advisorXie, MH-
dc.contributor.authorLokotko, Taras-
dc.date.accessioned2020-03-10T08:46:35Z-
dc.date.available2020-03-10T08:46:35Z-
dc.date.issued2019-
dc.identifier.citationLokotko, T.. (2019). Shape co-existence of neutron-rich 69, 71, 73Co nuclei. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.-
dc.identifier.urihttp://hdl.handle.net/10722/281303-
dc.description.abstractShell model works well in the valley of stability as it successfully explains the existence of magic numbers (2, 8, 20, 28, 50 ...). It was expected the shell model would work in regions far from stability. De- velopment of new facilities that work with radioactive beams opened a way to study nuclear physics far from stability. During recent exper- iments with unstable isotopes, interesting phenomena were revealed - new magic numbers started to evolve in the shell structure. For exam- ple, in proton closed shell of Ni nucleus (Z = 28) new magic number N = 40 was found. Theoretical development of many-body quantum systems revealed in- teresting phenomena in subatomic physics. On the one hand, stabilis- ing effects in closed shells and sub-shells lead nucleus to self-organise into spherical shapes. On the other hand, residual interactions, such as pairing forces between protons and neutrons, were forcing nucleus into deformed shape. Interplay between two opposite effects in someparticular nuclei exhibited energy eigenstates corresponding to differ- ent shapes. This phenomena is called shape coexistence, or shape isomerism. Discovering and interpreting these phenomena in nuclei close to the drip line is one of the most important topics in theoretical and experimental nuclear physics. Recently, the region around doubly magic radioactive isotope has drawn significant attention, as 68 68 Ni Ni was found to share spheri- cal features in ground state, while signatures of shape coexistence in the excited band were found. These experimental results motivate to study the region around magic numbers Z = 28, N = 40 for the evolu- tion of shape coexistence features. Moving along the N = 40 isotone line, only 2 protons less, the 66 Fe isotope was found quit deformed in ground state with no evidence of shape coexistence. Co isotopes are good candidates for studying shape isomerism in this region. 67 deformed Co was found to share features of both spherical 66 Fe. Shape coexistence of 67 a prolate proton-intruder state coupled to the of shape isomerism in Ni and Co is explained by the super- position of a proton f 7/2 hole state coupled to the spherical 67 68 66 68 Ni and Fe isotope. Existence Co pointed attention to shape evolution in heavier Co nuclei, namely 69,71,73 Co, and to shell transformation from N = 40 to N = 50. Shape coexistence of Co nuclei was studied during an in-beam gamma experiment at the Radioactive Isotope Beam Factory, RIKEN Nishina centre, Japan. 69,71,73 Co isotopes were produced via the knockout re- actions, when a secondary beam of 70,72,74 Ni and 72 Co nuclei at energy of 260 MeV/μ bombarded a liquid hydrogen target of MINOS device. The MINOS target was made with a length of 100mm to increase the total amount of nuclear reactions. The MINOS target chamber was surrounded by the time projection chamber which was used to reconstruct vertex of the reactions, improving energy resolution dur- ing the Doppler corrections. Energies of the γ-rays were measuredby the DALI2 NaI(Tl) detector array. Level scheme of low-lying ex- cited states was reconstructed using γ-γ coincidence technique. Lenzi- Nowacki-Poves-Sieja (LNPS) model of nuclear interaction was chosen for comparison with the experimental data. Strong signatures of shape coexistence were found in spectrums of 69,71 Co isotopes, as two struc- ture coexist - spherical and deformed bands. Due to the insufficient statistics only spherical structure were clearly seen in spectrum of 73 Co nucleus. In this thesis the evolution of shell structure in 69,71,73 Co isotopes will be discussed together with the physics behind shape co- existence in neutron-rich Co nuclei.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.rightsThis work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.-
dc.subject.lcshCobalt - Isotopes-
dc.subject.lcshNuclear physics-
dc.titleShape co-existence of neutron-rich 69, 71, 73Co nuclei-
dc.typePG_Thesis-
dc.description.thesisnameDoctor of Philosophy-
dc.description.thesislevelDoctoral-
dc.description.thesisdisciplinePhysics-
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.5353/th_991044104147403414-
dc.date.hkucongregation2019-
dc.identifier.mmsid991044104147403414-

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